thyroid and neurology

8/2/2019 Thyroid and Neurology

1/12

REVIEWPract Neurol 2009; 9: 145156

When to considerthyroid dysfunctionin the neurologyclinicNiraj Mistry, John Wass, Martin R Turner

There are many neurological manifestations of thyroid disease, and thyroidfunction has taken its place in the routine bloods of neurology practice.However, although conditions such as carpal tunnel syndrome prompt thyroidtesting despite any clear evidence for this approach, other symptoms of potential significance in terms of thyroid disease may be overlooked in thebusy general neurology clinic, or abnormal thyroid tests may be assumed to beincidental. Psychiatric disorders, loss of consciousness, movement disordersand weakness may all be manifestations of primary thyroid disease. This is asymptom-based review where we will consider the evidence (or lack of it) forthe association of various neurological problems with thyroid dysfunction,and also the pitfalls in interpretation of the biochemical tests.

The thyroid gland is essential for normalhuman development and maintenance.This becomes starkly apparent in theextreme circumstances of congenital

dysfunction (that is, cretinism), gross under-activity due to primary disease of the gland,

pituitary failure and thyroid storm. In mostsituations, however, the presentations of

thyroid disease are insidious, and becausethe actions of thyroid hormones are aspervasive as the nervous system itself, notsurprisingly there are many neurologicalmanifestations (table 1). Most patients pre-senting to general physicians on call will have

a thyroid stimulating hormone (TSH) level aspart of their admission bloods, frequently

N MistrySpecialist Registrar in Neurology,Nottingham University HospitalsNHS Trust

J WassProfessor of Endcrinology,Department of Endocrinology,Oxford University, Oxford, UK

M R TurnerMRC/MNDA Lady Edith WolfsonClinician Scientist and HonoraryConsultant Neurologist, OxfordUniversity, Oxford, UK

Correspondence to:Dr M TurnerDepartment of Clinical Neurology,West Wing Level 3, John Radcliffe

Hospital, Oxford OX3 9DU, UK;[email protected]

1Mistry, Wass, Turner

www.practical-neurology.com


2/12

one of many done already by the patientsgeneral practitioner because mild hypothyr-oidism is such a common problem and is so

often considered (incidence 410/100 000/yearin women and 60/100 000/year in men,increasing with age).1 The neurologist too, inthe outpatient clinic, is well-versed in check-ing the TSH as part of the dementia screen.In this article we will consider additional

symptoms that should prompt at least apassing thought to thyroid status, indicatewhere it is reasonable to assume thyroiddysfunction is the sole cause for a givenneurological problem, and review the pitfallsin the interpretation of thyroid tests.

PSYCHIATRIC SYMPTOMS ANDCOGNITIVE IMPAIRMENTHyperthyroidismAnxiety, agitation, restlessness, dysphoria,insomnia, depression and psychosis are thecore behavioural problems normally asso-ciated with hyperthyroidism (fig 1). Indeed,the misdiagnosis of bipolar or anxietydisorders is surprisingly frequent inhyperthyroid patients. Thyroid storm (acuterelease of thyroid hormones in alreadythyrotoxic patients) is the most dramaticpsychiatric presentation, where there may besevere agitation and altered behaviour.

Deterioration in cognitive function (mem-

ory, attention, planning and productivity) andemotional lability are also recognised mani-festations of hyperthyroidism.2 One of thereasons why this is easily missed is theclinical context: the symptoms may not berevealed in favour of a more obviouslyneurological symptom such as tremor, andeven then they are not necessarily explored.Or they are misinterpreted by the neurologistas a response to worrying neurologicalsymptoms, and not seen as their cause.

Treating overt hyperthyroidism in endo-crinology outpatients, unselected for psycho-logical symptoms, improves healthquestionnaire scores and psychologicalassessments, but in sub-clinical hyperthyroid-ism the evidence is conflicting.2, 3

There are reports of cognitive impairmentin up to half of elderly hyperthyroid patients,as well as presentations with lethargy anddepression termed apathetic thyrotoxicosis,but recent studies have shown no associationbetween thyroid hormone levels and cognitive

test scores.4, 5

Furthermore, thyrotoxic patientswho reported more memory, concentration

TABLE 1 Neurological manifestations of and associations with overthyperthyroidism and overt hypothyroidism

Neurological feature Hyperthyroidism Hypothyroidism

Anxiety +++ ++Depression ++ +++Cognitive impairment + /2 +++Hashimotos encephalopathy + +Myxoedema coma 2 ++Seizures + 2Cardiac syncope + 2Muscle weakness ++ +Myasthenia gravis + +Periodic paralysis + 2Peripheral neuropathy + +++Carpal tunnel syndrome + +++Tremor ++++ 2Chorea + 2Cerebellar ataxia 2 +Graves ophthalmopathy +++ 2 Visual field defects 2 ++Stroke ++ + /2Deafness 2 + /2Headache + +++Dysphonia + ++Cretinism 2 + (congenital)

Figure 1The typical appearance of severethyrotoxicosis. Dr M A Ansary/SciencePhoto Library.

Practical Neurology

10.1136/jnnp.2008.167163


3/12

and psychiatric impairment than controls wereno different on neuropsychological testing.5

Larger observational epidemiological studieswith objective measures are required toexamine the cognitive and psychologicaleffects of overt, compared to subclinical,

hyperthyroidism.If the TSH is undetectable, an underlying

cause should be sought (for example, Gravesdisease, toxic thyroid adenoma, rarely ovarianteratoma), and appropriate treatmentinitiated. Partial, but not complete TSHsuppression does not usually require ther-apeutic intervention when patients areasymptomatic.

Hypothyroidism

There is little debate that overt hypothyroid-ism is associated with depression andcognitive impairment, particularly in theelderly where executive function, processingspeed and memory are all impaired.6 But insubclinical hypothyroidism the data are con-flicting, and the small samples and cross-sectional surveys have not established acausal relationship with cognitive impair-ment. One small study showed improvementin depression and quality of life scores onrestoration of euthyroidism,2 and anothershowed the prevalence of depression insubclinical hypothyroidism to be 46% versus20% in the euthyroid control group.7 Bycontrast, in a prospective cross-sectionalstudy, people with subclinical hypothyroidismhad a similar frequency of mood disturbanceas euthyroid controls.3 Others have found noassociation between subclinical hypothyroid-ism and either mood disturbance or cognitiveimpairment.4, 8 Nonetheless, a trial of empiri-cal L-thyroxine may obviate the need for

antidepressants in some patients who havesubclinical hypothyroidism and depression,and should be consideredespecially inpatients with a TSH. 10 mU/l and positivethyroid antibodies. Little is known about themechanism of cognitive impairment anddepression in hypothyroidism.

Pernicious anaemiaAntibody-meditated pernicious anaemiaoccurs with increased frequency in autoim-

mune thyroiditis which may be associatedwith goitre (termed Hashimotos thyroiditis)

or an atrophic thyroid gland (termed Ordsthyroiditis); in both cases there is notnecessarily frank hypothyroidism. VitaminB12 measurements are therefore warranted(with a low threshold for supplementaryinjections) in the presence of cognitiveimpairment in patients with autoimmunethyroiditis.

Hashimotos encephalopathyThis is a controversial syndrome of highserum titres of anti-thyroid peroxidase (TPO)antibody (or occasionally anti-thyroglobulinor anti-thyroid microsomal antibodies) withencephalopathy, which responds to corticos-teroid treatment. TPO is an enzyme in thyroidfollicular cells that oxidises iodide andfacilitates its addition to tyrosine residueson thyroglobulin to produce thyroxineT4,and triiodothyronineT3. The clinical featuresof Hashimotos encephalopathy includestroke-like episodes (27%), seizures (66%),psychosis (38%), raised cerebrospinal fluid

protein (78%) and abnormal EEG (98%).Thyroid function may show anything from

TABLE 2 Definitions

Syndrome Definition

Cretinism Severely stunted physical and mental development due tountreated congenital hypothyroidism

Graves disease Hyperthyroidism and eye disease caused by TSH receptorstimulating auto-antibodies

Gravesophthalmopathy

Exophthalmos due to autoimmune orbitopathy (in additionto the widened palpebral fissure, lid lag and lid retractionfound in hyperthyroidism of any cause)

Hashimotosencephalopathy

A syndrome of encephalopathy and high serum antithyroidantibody concentrations that is responsive tocorticosteroid therapy

Hashimotosthyroiditis

Also known as chronic lymphocytic thyroiditis:autoimmune inflammation of the thyroid gland usuallyresulting in hypothyroidism

Overt

hyperthyroidism

Thyrotropin (TSH) is suppressed and free thyroxine (fT4) or

free triiodothyronine (fT3) levels are above the normalreference rangeOverthypothyroidism

Raised TSH with low fT4 and fT3

Subclinicalhyperthyroidism

Low or undetectable concentration of serum thyrotropin(TSH) with free triiodothyronine (fT3) and free thyroxine(fT4) levels within the normal reference ranges

Subclinicalhypothyroidism

Raised TSH but fT4 and fT3 in the normal range




4/12

overt hypothyroidism to overt hyperthyroid-ism, most commonly subclinical hypothyroid-ism (35%).9 The diagnosis tends to be madeafter exclusion of the more common toxic,metabolic and infective causes for encephalo-pathy. The cause is unknown; although titresof anti-TPO antibodies fall in response tosteroids, they are not clearly pathogenic.Since its first description in 1966, to 2002,only 85 cases have been reported in theliterature that met the criteria of impairedconsciousness or cognition, no evidence of bacterial or viral infection on cerebrospinalfluid analysis, and high serum titres of anti-TPO, anti-thyroid microsomal, or anti-thyr-

oglobulin antibodies.9

LOSS OF CONSCIOUSNESSMyxoedema comaThe incidence of myxoedema coma in Europeis 0.02/100 000/year.10 It is due to decom-pensation of severe untreated hypothyroid-ism, which the neurologist should alwaysconsider during an intensive care unit (ICU)consult. The precipitant can be any systemicinsult including sepsis, stroke, cold, burns,

gastrointestinal haemorrhage and drugs(which are not limited to anaesthetics). In

the presence of a raised TSH with low T3 andT4, other features of myxoedema comainclude:

N

confusionN hypothermiaN hyponatraemia which may compound the

central nervous system (CNS) depressionand provoke seizures

N haemodynamic instabilityN respiratory acidosis due to blunted

respiratory centre responses to bothhypercapnoea and hypoxia.11

Missing the diagnosis is potentially cata-strophic so TSH must be measured in everycomatose patient with no obvious cause,especially in the presence of hypothermia,hyponatraemia or hypercapnoea (as well asthe usual signs of hypothyroidism). Weadvocate more rapidly-acting T3 in smallintravenous doses as initial treatment (5mg8-hourly) rather than T4, with supportive careon an ICU (slow warming, fluid resuscitationand ventilation if needed), and treatment of any concomitant conditions (for example,sepsis, hyponatraemia with hydrocortisone

until any coexistent adrenal insufficiency hasbeen excluded).11 Vitamin B12 levels should

TABLE 3 Thyroid-related conditions with their clinical, biochemical andimmunological features

Condition Clinical state TSH fT4 fT3 Antibodies

Graves disease Hyperthyroid Low High High + ve TSH receptorGravesophthalmopathy

Eye disorderindependent of thyroidor antibody status

NA NA NA NA

Autoimmunethyroiditis(Hashimotoswithgoitre; Ordsatrophic)

Usually hypothyroid;can be euthyroid; caneven be transientlyhyperthyroid insubacute phase

High Low Low + ve thyroidperoxidase,thyroglobulin, orthyroidmicrosomal

Hashimotosencephalopathy

Encephalopathic;typically hypothyroid,but may be euthyroidor rarely hyperthyroid

High Lownormal

Lownormal

+ ve TPO,thyroglobulin, orthyroidmicrosomal

Myxoedema coma Severely hypothyroid High Low Low NAPituitary failure Hypothyroid Low/normal

Low Low NA

Sick euthyroid Euthyroid Variable Variable Variable NA

fT3, free triiodothyronine; fT4, free thyroxine; NA, test not applicable; TPO, anti-thyroidperoxidase antibody; TSH, thyroid stimulating hormone.

Practical Neurology

10.1136/jnnp.2008.167163


5/12

also be measured in view of the association of pernicious anaemia with autoimmune thyr-oiditis.

Thyrotoxic seizuresFocal or generalised seizures are a rare, buteasily missed presenting feature of thyrotox-icosis. Although generally considered uncom-mon, one series reported them in 9% of alladmissions with thyrotoxicosis.12 Amongpatients with newly presenting seizures, thereare no epidemiological data but thyrotoxicosismust be an exceedingly rare cause (our localepileptologist Dr Yvonne Hart recalls twocases in the last 15 years). EEG findingsinclude diffuse slowing, sharp waves, burstsof poly spikes and slow waves, and prolonged

photic response. Non-specific EEG abnormal-ities are present in up to two thirds of thyrotoxic patients, even those withoutseizures.12 The absence of coexisting serumelectrolyte, glucose or osmolarity abnormal-ities, as well as the resolution of seizures withtreatment for thyrotoxicosis without anti-epileptic drugs, suggests a direct seizurethreshold lowering effect of thyroid hormone.

Cardiac syncopeThyrotoxicosis is a well known cause of sinustachycardia, atrial fibrillation and atrial flut-ter, with palpitations being the most commonpresentation that invariably prompts consid-eration of thyroid status. Cardiac syncope inthyrotoxicosis is much less common, and ismediated by either second or third degreeatrioventricular conduction block (throughuncertain mechanisms) causing Stokes-Adams syncope or generalised seizures dueto cerebral anoxia.13 Most cases occur in thecontext of Graves disease.

MUSCLE PROBLEMSHyperthyroid myopathyThyrotoxicosis can cause weakness andwasting with a predilection for pelvic andshoulder girdle musculature, typically withoutmyalgia.14 It probably only occurs in thecontext of obvious thyrotoxicosis with sig-nificant weight loss (our colleague Dr DavidHilton-Jones recalls only one patient in 30years of muscle specialisation whopresented

with weakness manifest by inability to per-form a 180u turn of her double-decker

London bus at Crystal Palace!). Very rarely,rhabdomyolysis has been reported as part of thyroid storm.15

Although weakness is hardly ever a pre-senting symptom, established hyperthyroid-ism is more likely to produce weakness than

hypothyroidism (but the prognosis of anyweakness is better in hyperthyroidism).16 Aprospective series reported 62% of hyperthyr-oid patients had weakness in at least onemuscle group on manual muscle strengthtesting, rising to 81% on hand-held dyna-mometry (correlating with free T4 concentra-tions, but not serum creatine kinase (CK)).16

There is little evidence for an underlyingmyopathic process; there are no histologicalmyopathic features specific to hyperthyroid-ism and typically weakness is rapid in onset,can be severe, yet responds rapidly totreatment.16 Therefore, weakness inhyperthyroidism should be considered aphysiological rather than a myopathic phe-nomenon (except in those very rare caseswith rhabdomyolysis).

Treatment is with restoration of euthyroid-ism combined with beta-blockers, both of which give subjective and objective improve-ment in weakness.17

Hypothyroid myopathyHypothyroid patients commonly complain of pain, cramps and muscle stiffness. Proximalweakness is also common.16 Typical findingsare pseudomyotonia (slow relaxation of muscle after contraction) and prolongedtendon reflex relaxation (fig 2).Myo edema(the mounding phenomenon) occurs inaround one third of patients, and is due toslow sarcolemmal reabsorption of calcium;

Figure 2Method for obtaining the ankle-jerkreflex with the patient kneeling.49

Reproduced with permission fromLippincott Williams & Wilkins.




6/12

percussion of a muscle causes a small lump torise where the tendon hammer was struck,receding within a minute. On electromyogra-phy this is electrically silent, unlike percussionmyotonia. The same phenomenon occurs inmalnutrition.

The rare Hoffmanns syndrome is charac-terised by muscle hypertrophy, weakness andslow, clumsy movements in the context of hypothyroidism. Its paediatric counterpartKocher-Debre -Semelaigne syndrome consistsof proximal weakness with muscular pseudo-hypertrophy in children with congenitalthyroid insufficiency.

In a prospective cohort of hypothyroidpatients, 54% complained of weakness and42% complained of fatigability, muscle pain,

stiffness or cramps. Overall 79% had some sortof complaint suggestive of muscle dysfunction.However only 3% had muscular symptoms asthe presenting complaint. Clinically 38% hadweakness on manual muscle testing (mainlyproximal), rising to 58% when tested with

hand held dynamometry.16 On neurophysiolo-gical testing, 33% had myopathic change andserum CK was raised in 37% of patients (butwith no correlation between weakness and CK,TSH, T3, or T4).16 If muscle biopsy is performedin hypothyroidism to exclude other diagnoses,

the findings are non-specific, typically justshowing type II fibre atrophy (Dr Hilton-Jones,personal communication). Hypothyroidism hasalso been postulated to lower the threshold forrhabdomyolysis.18

Symptoms from hypothyroid myopathymay take several months to recover despitetreatment.

Statins used to treat hypercholesterolemiacan cause muscle symptoms similar to thosefound in hypothyroidism, and they may alsocause a raised CK. Because hypothyroidism isassociated with both hypercholesteroleamiaand raised serum CK, some suggest that allhypercholesterolaemic patients should havetheir thyroid function as well as CK checkedbefore starting a statin, just in case they havehypothyroidism.

THYROID DYSFUNCTION ANDTHE NEUROMUSCULARJUNCTIONMyasthenia gravisThere is an association between autoimmunethyroid disorders and myasthenia gravis; in aseries of myasthenia patients, 8% had Gravesdisease and 4% had Hashimotos thyroiditis.19

The patients with myasthenia and Graves hada younger age of onset of their myasthenicsymptoms (average 35 vs 49 years), were lesslikely to have anti-acetylcholine receptorantibodies (44% vs 90%), and were morelikely to have thymic hyperplasia (73% vs18%) compared to patients with myasthenia

gravis and no other autoimmune disease; themyasthenia treatment response of bothgroups was the same.19 Therefore, whenassessing thyrotoxic neuromuscular weak-ness, it is important to always considermyasthenia gravis; any severe respiratoryfailure is more likely to be due to unmaskingof coexistent myasthenia gravis.20

THYROTOXIC PERIODICPARALYSIS

Due to worldwide migration, this henstooth of UK neurology is increasingly seen

TABLE 4 Non-neurological symptoms and signs in hyperthyroidism andhypothyroidism

Hyperthyroidism Hypothyroidism

Symptoms:l Heat intolerance, sweating l Tirednessl Palpitations l Dry skinl Weight loss with increased

appetitel Altered facial appearancel Feeling cold

l Diarrhoea l Hair dry, unmanageable and thinningl Steatorrhoea l Constipationl Polyuria l Weight gain with poor appetitel Oligomenorrhoea l Dyspnoeal Amenorrhoea l Hoarse voicel Loss of libido l Menorrhagia (later, oligomenorrhoea

or amenorrhoea), decreased libidoSigns:l Sinus tachycardia l Dry coarse skinl Atrial fibrillation in the elderlyl Cool peripheriesl Warm, moist skin l Puffy face, hands, and feetl Goitre l Yellow skinl Palmar erythema, onycholysis,

pruritus, urticaria, diffusepigmentation

l Diffuse alopecial Bradycardial Peripheral oedema

l Diffuse alopecia l Serous cavity effusionsl Gynaecomastia l Galactorrhoea (raised prolactin)

l Enlarged salivary glands

Adapted from the Oxford textbook of medicine , Oxford University Press.

Practical Neurology

10.1136/jnnp.2008.167163


7/12

in Western countries, as well as in the orientalAsian populations (where it is typically found).In Chinese and Japanese thyrotoxic patientsabout 2% have periodic paralysis, far more inmen than in females, with onset usuallybetween 20 and 40 years of age.21 The

patients have an underlying tendency formuscle Na/K-ATPase overactivity duringhyperthyroidism (of any cause), provokedfurther by insulin, catecholamines, or exercise.This Na/K-ATPase overactivity drives serumpotassium into the intracellular compartmentcausing hyperpolarisation, apparent hypoka-laemia and weakness.21

Typical patients are young adult males withfrequent attacks of transient weakness ran-ging from mild proximal weakness to com-

plete flaccid paralysis, usually with no familyhistory. Episodes usually occur a few hoursafter large carbohydrate meals, during theearly hours of the morning, or during restafter exercise. Bulbar and respiratory involve-ment, and ventricular arrhythmias, areuncommon but can occur. There are nosensory features. Attacks are more commonin the summer. Bedside findings includetachycardia, systolic hypertension and hypor-eflexia. Features of underlying hyperthyroid-ism may be subtle or clinically silent with onlymildly deranged thyroid hormones.21, 22

ECG changes include sinus tachycardia,large voltage QRS complexes and first degreeatrioventricular block. Electromyographyshows reduced amplitude compound muscleaction potentials. Biochemical features aresuppressed TSH (unless a pituitary TSH-oma isthe cause) with raised T3 and T4, raised CK,hypokalaemia, hypophosphataemia (withlevels of potassium and phosphate in urinebeing low) and hypercalciuria. With the

exception of hyperthyroidism, electrophysio-logical and biochemical features disappear inbetween episodes.22

Treatment of attacks is with potassiumsupplementation (intravenously if there issevere weakness or respiratory/bulbar com-promise) and high dose non-selective beta-blockers (propranolol). As low a dose of potassium as possible (, 10 mmol/h potas-sium chloride iv with titration determined byhourly serum level monitoring) has been

advocated to avoid rebound hyperkalaemia.IV or oral propranolol (34 mg/kg) alone may

be efficacious, though there are no trial data.Prophylaxis with propranolol (40 mg fourtimes daily) is effective, while prophylacticpotassium supplements have no value.Definitive treatment is identification andcorrection of the thyroid disorder, which

eradicates further attacks. An importantpractice point is that although acetazolamideis an effective treatment for non-thyrotoxicforms of periodic paralysis, it must not beused in thyrotoxic periodic paralysis where itprecipitates attacks.22

PERIPHERAL NEUROPATHY Hyperthyroid neuropathyAlthough less frequently described than inhypothyroidism, hyperthyroidism is associated

with peripheral neuropathy. A prospectivestudy found that in the hyperthyroid group,14% complained of numbness and paraesthe-sias, and 19% had signs of distal sensorydisturbance in the limbs with depressed ankle jerks. Neurophysiological testing confirmed apredominantly sensory axonal neuropathy in24%. With treatment of hyperthyroidism thesensory complaints in all these patientsresolved within seven months.16

Hypothyroid neuropathyPeripheral neuropathy is common inhypothyroidism and typically manifests asglove and stocking numbness, paraesthesiaand painful dysaesthesia. One series found64% of hypothyroid patients complained of neuropathic symptoms, most commonlyparaesthesias, and 33% had signs consistentwith neuropathy, most commonly loss of deep tendon reflexes. On neurophysiologicaltesting 72% had evidence of a polyneuro-pathy in this series,23 and the literature citesboth demyelinating24 and axonal25 variants,and no correlation with the degree of hypothyroidism. A recent study of neurologi-cally asymptomatic hypothyroid patients founda predominantly motor demyelinating patternin 52%, suggesting that motor nerve abnorm-alities do occur but are less likely to besymptomatic (and less widely reported).24

Overall, the pathogenesis is poorly understood.In a cohort of seven hypothyroid patients

who had neurophysiologically evident poly-

neuropathy before treatment, the four withdemyelinating features had significant




8/12

neurophysiological improvement threemonths into treatment, in contrast to theaxonal variants. Clinical improvement waspresumed based on these findings, but thiscohort did not necessarily have neurologicalsymptoms to start with.26

There are reports of autoimmune demye-linating polyradiculoneuropathy (includingGuillain-Barre, chronic inflammatory demye-linating polyradiculopathy and Miller Fishersyndrome), and multifocal motor neuropathyin patients with Hashimotos thyroiditis (anautoimmune disease in which thyroid cellsare destroyed by autoantibodies to thyroidantigens including TPO, and anti-thyroglobu-lin, and TSH receptor blocking antibodies).Treatment in these cases should includesuppression of the underlying autoimmunity,not just thyroid replacement alone.

CARPAL TUNNEL SYNDROMECarpal tunnel syndrome is common inhypothyroidism, 25% meeting neurophysio-logical criteria, and several studies reportimprovement when euthyroidism is restored.16

However, the symptoms can persist inhypothyroid patients even when they becomeeuthyroid and no longer have prolongedmedian nerve latencies at the wrist.27 Carpaltunnel syndrome in hyperthyroidism is muchless common; nerve conduction and symp-toms improve with treatment of hyperthyr-oidism.28 The mechanism is unclear.

The diagnostic yield from screening allpatients with carpal tunnel syndrome is poor;over 200 patients have to be tested for onenew diagnosis of hypothyroidism to be madeat a cost of just over 1000. The cost isfourfold lower for the detection of diabetesmellitus. A formal cost-benefit analysis for

empirical blood tests would probably befavourable for diabetes, rather than hypothyr-oidism testing (despite equally low positive-predictive-value of carpal tunnel syndromefor both diabetes and hypothyroidism).29

MOVEMENT DISORDERSHyperthyroid tremorA persistent fine tremor occurs in mosthyperthyroid patients, mostly in the hands,exacerbated with the arms outstretched and

fingers spread. Tremor can also affect thehead, face, vocal cords, trunk and legs.14 It is

mediated by adrenergic hypersensitivity anddramatic improvement is often achieved withbeta-blockers until euthyroidism is restored.

ChoreaA rare, often well-remembered neurological

manifestation of hyperthyroidism is chorea,and is sometimes the presenting feature.Typically it occurs before the age of 40,responds well to beta-blockers and resolveswhen euthyroidism is restored.14

Hypothyroid ataxiaCerebellar (predominantly gait) ataxia is welldescribed in hypothyroidism and was recog-nised in the late nineteenth century. Limbataxia and dysarthria occur less commonly. Ithas been attributed to the metabolic andphysiological effects of hypothyroidism andusually resolves on treatment of hypothyr-oidism. In cases where there is no resolutionwith thyroid replacement (often inHashimotos thyroiditis) an autoimmunemechanism for cerebellar dysfunction hasbeen postulated, suggesting a trial of immu-nomodulatory therapy.30

VISUAL SYMPTOMSThe term thyroid eye disease is often used

synonymously with Graves ophthalmopa-thy and goes beyond the lid lag andretraction (effected by overactivity of thesympathetically innervated portion of levatorpalpebrae superioris) which occurs inhyperthyroid states of any cause. In Gravesophthalmopathy there is retro-orbital inflam-mation and lymphocytic infiltration, and it isindependent of clinical thyroid status. In arecent comprehensive account of thyroid eyedisease it was noted that 2550% of patientswith Graves disease were affected by Gravesophthalmopathy (the fact that women arefive times more likely to have Gravesophthalmopathy is only because Gravesdisease is more common in women).31

Typical clinical features are painful or grittyeyes, photophobia, chemosis, exophthalmosand diplopia. When signs of optic neuropathyoccur (reduced acuity, impaired colour vision,field loss and relative afferent papillarydefect) an urgent ophthalmological reviewshould be sought, as early intervention

improves outcome.31

Graves ophthalmopathycan occur in one eye alone, can precede any

Practical Neurology

10.1136/jnnp.2008.167163


9/12

history of Graves disease itself, and opticneuropathy can precede obvious proptosis.31

Symptomatic treatment (for example, arti-ficial tears) and smoking cessation aresufficient in most patients but up to onethird may require attempts at disease mod-

ification, either with steroids or orbital radio-therapy. Inferior orbital decompression canhelp proptosis in severe cases.31

Visual field defectsIn a cohort of patients with primaryhypothyroidism 70% had pituitary enlarge-ment on MRI.32 In an earlier study 71% hadvisual field defects on Goldmann perimetry,although only 14% of these were sympto-matic, and the typical changes were restric-

tion to the central visual field, with peripheralvision being less commonly affected.33

Pituitary volume did not correlate with thedegree of visual field defect in this study, butdid correlate with serum TSH levels. Pituitaryenlargement and visual field defects improvedwith thyroid replacement.

STROKEOvert hypothyroidism is associated with anincreased prevalence of hypertension, hyper-lipidaemia and hyperhomocysteinaemia. Byvirtue of this an increased risk of stroke seemslikely but there are no direct studies.Hyperthyroidism is associated with ischaemicstroke mediated by atrial fibrillation (AF) andembolism from the heart. Analysis of theFramingham cohort found a threefoldincreased risk (during 10 year follow-up) of developing AF in those over 60 years of agewith a low serum TSH.34 There is stillcontroversy whether thyrotoxic AF confers agreater risk of stroke than AF of other causes.

There is evidence of hypercoagulability inhyperthyroidism, and the incidence of intra-cranial venous thrombosis is greater thanexpected by chance alone.35

MISCELLANEOUS SYMPTOMSHearing lossCongenital hypothyroidism is known to causeirreversible sensorineural hearing impairmentif severe. The relationship is less clear foracquired deafness in adult onset hypothyr-

oidism. There are reports of hearing impair-ment and tinnitus but the many brainstem

evoked potential, audiometric and histologicalstudies have conflicting results. The site of any lesion thought to cause deafness inhypothyroidism also remains contentious.

HeadacheThere are a few case reports of headache as apresenting symptom of hyperthyroidism,either alone or accompanied by nausea andvomiting (reported cases also have derangedliver function).36 As many as 30% of patientswith hypothyroidism suffer from headachealthough the mechanism, if there really is anassociation, is unknown.37

DysphoniaIndependent of thyroid hormone status, a

goitre (which may be euthyroid) compressingthe recurrent laryngeal nerve may causedysphonia. In hypothyroidism dysphonia isthought to be due to laryngeal myxoedema(fig 3). Hyper IgG4 syndrome (multifocalfibrosclerosis) is associated with Riedelsthyroiditis causing dysphonia and dyspnoea.38

Thyroid malignancyThyroid malignancy metastasising to the brainis rare (1% of all thyroid malignancies). In acase series, biopsies of brain metastaseswere subclassified as 10 papillary carcinomas,2 follicular carcinomas, 1 Hurthle cell

Figure 3An 80-year-old woman with

hyperthyroidism. Dr P Marazzi/SciencePhoto Library.




10/12

carcinoma, 1 medullary carcinoma, 1 insularcarcinoma and 1 anaplastic carcinoma. Mostbrain metastases are solitary, and so surgicalresection is advocated, with radiosurgery orradiotherapy reserved for those with atechnically difficult single metastasis, or

multiple intracranial metastases.39 There arealso case reports of spinal cord compressingmetastases.40 Other problems include cerebel-lopontine angle metastasis from papillarycarcinoma of the thyroid,41 medullary thyroidcarcinoma causing hypercoagulability withmarantic endocarditis and multiple strokes,42

and Horners syndrome in benign andmalignant thyroid tumours.43

Sleep disordersIn a cohort of 20 hypothyroid patients 10%had moderate to severe obstructive sleepapnoea syndrome (OSAS) and 15% had milderforms. In those with both OSAS andhypothyroidism, respiratory drive wasimpaired, which was restored with thyroidhormone replacement44 In another cohort of 65 patients with proven OSAS, only two werediscovered to have hypothyroidism.44 Thereare reports of sleepwalking associated withGraves disease. A causal association was

postulated because sleepwalking episodescoincided with the onset of thyrotoxicosisand resolved on achievement of euthyroidism.This may be due to prolonged non-REM sleepand associated fatigue.45

LATE EFFECTS OF CONGENITALHYPOTHYROIDISMIodine deficiency is globally the single biggestcause of preventable brain damage andmental retardation; not surprisingly many

studies have assessed the sequelae of con-genital hypothyroidism where iodine defi-ciency was the cause. The severity of theneurological complications correlates with theseverity of iodine deficiency, with overtendemic cretinism (mental retardation, deaf mutism, strabismus, spastic diplegia, rigidity,shuffling gait) being the worst. The typicalpattern of spasticity involves the trunk andproximal limbs with relatively unaffectedhands and feet, resembling extrapyramidal

basal ganglia rather than corticospinal invol-vement, and correlating with basal ganglia

signal changes demonstrated on MRI con-sistent with gliosis.46

Even in early treated congenitallyhypothyroid children, those with severehypothyroidism have significantly poorerperformance in balance, coordination and

fine motor ability (compared to controls andthe less severe hypothyroid group) at 3-, 5-and 7-year-old follow-up. Cognitive perfor-mance was not significantly different tocontrols, but language disorders were foundin half of all congenitally hypothyroidchildren at 3 and 5 years of age, suggestinglanguage development is particularly at risk.47

NEUROLOGICAL ADVERSEEFFECTS OF ANTI-THYROID

MEDICATIONCarbimazole can cause headache, and rarely amyopathy. Sometimes propylthiouracil cancause encephalopathy. In overdose L-thyrox-ine can produce acute tremor, restlessness,excitability, insomnia, headache, musclecramps and weakness.

INTERPRETATION OF BLOODRESULTSA rationale for sensible and cost-effective

ordering and interpretation of thyroid func-tion tests has been proposed.48 To summarisethis and other points of caution:N Assaying TSH alone is a suitable and

sensitive screening test for thyroid dis-ease, especially in cases with a low pre-test probability.

N If the TSH is high, tests for free thyroxine(fT4), and thyroid antibodies should berequested (eg, anti-TPO, anti-TSH receptorantibodies). If fT4 is normal, factorsbiasing towards treatment would be

positive antibodies or other autoimmunedisease, previous history of Graves dis-ease or TSH. 10 mU/l.

N If the TSH is low, then fT4 (often with fT3measurement, which is more sensitive)will establish whether the patient ishyperthyroid. TSH receptor antibodiesshould also be checked.

N Patients with Graves disease on anti-thyroid drugs require more caution ininterpretation of their thyroid function.TSH levels can remain low for some

months after the patient becomeseuthyroid. The presence of positive

Practical Neurology

10.1136/jnnp.2008.167163


11/12

antibodies in Graves disease makes laterhypothyroidism more likely.

N In pituitary disease the fT4, not the TSH(which will be low), is used to diagnoseand monitor thyroid hormone replace-ment

N A clinically euthyroid patient with unex-pectedly high or low T4 (total, ie, free+bound) may have altered thyroid bindingglobulin levels (which can be hereditary,and also change in pregnancy and withoestrogen use). Usually no treatment isrequired.

N Phenytoin, carbemazepine, non-steroidalanti-inflammatory drugs, corticosteroidsand propranolol have all been associatedwith falsely low T4 and T3 levels.

N In patients taking amiodarone, manage-ment is generally guided by the clinicalrather than the biochemical thyroid state,but expert guidance should be sought.

The sick euthyroid syndrome refers toderanged thyroid function tests in patientswithout pre-existing hypothalamic, pituitaryor thyroid gland dysfunction who haveanother illness. The thyroid function testsusually revert to normal when the non-thyroid illness resolves.

ACKNOWLEDGEMENTSWe are very grateful to Dr David Hilton-Jones(Consultant Neurologist and muscle diseasesubspecialist) for his helpful specific commentson thyroid-related muscle symptoms andsigns. This article was reviewed by AndrewChancellor, Tauranga, New Zealand.

REFERENCES1. Vanderpump MP, Tunbridge WM, French JM,et al .

The incidence of thyroid disorders in the

community: a twenty-year follow-up of theWhickham Survey.Clin Endocrinol (Oxf) 1995;43 :5568.

2. Gulseren S, Gulseren L, Hekimsoy Z,et al .Depression, anxiety, health-related quality of life,and disability in patients with overt and subclinicalthyroid dysfunction.Arch Med Res 2006;37 :1339.

3. Larisch R, Kley K, Nikolaus S,et al . Depression andanxiety in different thyroid function states.HormMetab Res 2004;36 :6503.

4. Gussekloo J, van Exel E, de Craen AJ,et al . Thyroidstatus, disability and cognitive function, andsurvival in old age.JAMA2004;292 :25919.

5. Vogel A, Elberling TV, Hrding M,et al . Affectivesymptoms and cognitive functions in the acutephase of Graves thyrotoxicosis.Psychoneuroendocrinology 2007;32 :3643.

6. Davis JD, Tremont G. Neuropsychiatric aspects of hypothyroidism and treatment reversibility.Minerva Endocrinol 2007;32 :4965.

7. Almeida C, Brasil MA, Costa AJ,et al . Subclinicalhypothyroidism: psychiatric disorders andsymptoms.Rev Bras Psiquiatr 2007;29 :1579.

8. Roberts LM, Pattison H, Roalfe A,et al . Is subclinicalthyroid dysfunction in the elderly associated withdepression or cognitive dysfunction?Ann InternMed 2006;145 :57381.

9. Chong JY, Rowland LP, Utiger RD. Hashimotoencephalopathy: syndrome or myth?Arch Neurol 2003;60 :16471.

10. Galofre JC, Garca-Mayor RV. Densidad deincidencia del coma mixedematoso.Endocrinologia 1997;44 :103104.

11. Kwaku MP, Burman KD. Myxedema coma.J Intensive Care Med 2007;22 :22431.

12. Jabbari B, Huott AD. Seizures in thyrotoxicosis.Epilepsia 1980;21 :916.

13. Miller RH, Corcoran FH, Baker WP. Second and thirddegree atrioventricular block with Graves disease:a case report and review of the literature.Pacing Clin Electrophysiol 1980;3:70211.

14. Kung AW. Neuromuscular complications of thyrotoxicosis.Clin Endocrinol (Oxf) 2007;67 :64550.

15. Bennett WR, Huston DP. Rhabdomyolysis in thyroidstorm. Am J Med 1984;77 :7335.

Video of examination of thyroid status and thyroidgland http://www.youtube.com/watch?v=krXoyP5j5lk

PRACTICE POINTS

l Overt hypothyroidism causes depression and cognitive impairment, but anyassociation of cognitive impairment with subclinical hypothyroidism andthyrotoxicosis is uncertain.

l Loss of consciousness can be due to underlying thyroid dysfunction(including thyrotoxic seizures), and missing the diagnosis of myxoedemacoma is particularly hazardous.

l The exceedingly rare diagnosis of Hashimotos encephalopathy remainscontroversial.

l Hyperthyroidism is more likely to be associated with muscle weakness thanhypothyroidism, but weakness is rarely the presenting feature in either, andthyrotoxic myopathy remains a controversial condition.

l Because hypothyroidism is associated with raised cholesterol, and bothstatins and hypothyroidism can cause raised CK and muscle symptoms,TSH and CK should be checked in all patients before starting statins.

l Neuropathy is more frequently described in hypothyroidism than inhyperthyroidism, and is predominantly sensory in both.

l Over 200 carpal tunnel patients have to have thyroid function testing todiagnose one with hypothyroidism.l There is a clear and important association between autoimmune thyroid

disorders and myasthenia gravis, and both must be considered in the weakpatient.

l With increasing worldwide migration, thyrotoxic periodic paralysis isbecoming less rare outside its typical setting of China and Japan;acetazolamide precipitates attacks and must not be given.

l Only 2550% of patients with Graves disease have ophthalmopathy.l Iodine deficiency is globally the single biggest cause of preventable brain

damage and mental retardation.l Drugs used to treat hyperthyroidism can cause headache, myopathy and

encephalopathy.




12/12

16. Duyff RF, Van den Bosch J, Laman DM,et al .Neuromuscular findings in thyroid dysfunction: aprospective clinical and electrodiagnostic study.J Neurol Neurosurg Psychiatry 2000;68 :7505.

17. Olson BR, Klein I, Benner R,et al . Hyperthyroidmyopathy and the response to treatment.Thyroid 1991;1:13741.

18. Halverson PB, Kozin F, Ryan LM,et al .

Rhabdomyolysis and renal failure inhypothyroidism.Ann Intern Med 1979;91 :578.

19. Kanazawa M, Shimohata T, Tanaka K,et al . Clinicalfeatures of patients with myasthenia gravisassociated with autoimmune diseases.Eur J Neurol 2007;14 :14034.

20. Lakhal K, Blel Y, Fysekidis M,et al . ConcurrentGraves disease thyrotoxicosis and myastheniagravis: the treatment of the former maydangerously reveal the latter.Anaesthesia 2008;63 :8769.

21. Kung AW. Clinical review: Thyrotoxic periodicparalysis: a diagnostic challenge.J Clin Endocrinol Metab 2006;91 :24905.

22. Lin SH. Thyrotoxic periodic paralysis.Mayo ClinProc 2005;80 :99105.

23. Beghi E, Delodovici ML, Bogliun G,et al .Hypothyroidism and polyneuropathy.J Neurol Neurosurg Psychiatry 1989;52 :14203.

24. El-Salem K, Ammari F. Neurophysiological changesin neurologically asymptomatic hypothyroidpatients: a prospective cohort study.J ClinNeurophysiol 2006;23 :56872.

25. Pollard JD, McLeod JG, Honnibal TG,et al .Hypothyroid polyneuropathy. Clinical,electrophysiological and nerve biopsy findings intwo cases. J Neurol Sci 1982;53 :46171.

26. Kececi H, Degirmenci Y. Hormone replacementtherapy in hypothyroidism and nerve conduction

study. Neurophysiol Clin2006;36 :7983.27. Palumbo CF, Szabo RM, Olmsted SL. The effects of hypothyroidism and thyroid replacement on thedevelopment of carpal tunnel syndrome.J Hand Surg [Am] 2000;25 :7349.

28. Roquer J, Cano JF. Mononeuropathies inthyrotoxicosis.J Neurol Neurosurg Psychiatry 1992;55 :332.

29. de Rijk MC, Vermeij FH, Suntjens M,et al . Does acarpal tunnel syndrome predict an underlyingdisease?J Neurol Neurosurg Psychiatry 2007;78 :6357.

30. Selim M, Drachman DA. Ataxia associated withHashimotos disease: progressive non-familial adultonset cerebellar degeneration with autoimmune

thyroiditis.J Neurol Neurosurg Psychiatry 2001;71 :817.

31. Cawood T, Moriarty P, OShea D. Recentdevelopments in thyroid eye disease.BMJ 2004;329 :38590.

32. Khawaja NM, Taher BM, Barham ME,et al . Pituitaryenlargement in patients with primaryhypothyroidism.Endocr Pract 2006;12 :2934.

33. Yamamoto K, Saito K, Takai T,et al . Visual fielddefects and pituitary enlargement in primaryhypothyroidism.J Clin Endocrinol Metab 1983;57 :2837.

34. Sawin CT, Geller A, Wolf PA,et al . Low serumthyrotropin concentrations as a risk factor for atrialfibrillation in older persons.N Engl J Med 1994;331 :124952.

35. Verberne HJ, Fliers E, Prummel MF,et al .Thyrotoxicosis as a predisposing factor for cerebralvenous thrombosis.Thyroid 2000;10 :60710.

36. Ashawesh K, Abdulqawi R, Ahmad S.Hyperthyroidism presenting with persistentvomiting, headache and deranged liver functiontests. Eur J Intern Med 2008;19 :72.

37. The International Classification of HeadacheDisorders, 2nd edition.Cephalalgia 2004;24 (Suppl1):1160.

38. Tutuncu NB, Erbas T, Bayraktar M,et al . Multifocalidiopathic fibrosclerosis manifesting with Riedelsthyroiditis.Endocr Pract 2000;6:4479.

39. McWilliams RR, Giannini C, Hay ID,et al .Management of brain metastases from thyroid

carcinoma: a study of 16 pathologically confirmedcases over 25 years.Cancer 2003;98 :35662.

40. Goldstein SI, Kaufman D, Abati AD. Metastaticthyroid carcinoma presenting as distal spinal cordcompression.Ann Otol Rhinol Laryngol 1988;97 :3936.

41. Cha ST, Jarrahy R, Mathiesen RA,et al .Cerebellopontine angle metastasis from papillarycarcinoma of the thyroid: case report and literaturereview.Surg Neurol 2000;54 :3206.

42. Lal G, Brennan TV, Hambleton J,et al . Coagulopathy,marantic endocarditis, and cerebrovascular accidentsas paraneoplastic features in medullary thyroidcancercase report and review of the literature.Thyroid 2003;13 :6015.

43. Leuchter I, Becker M, Mickel R,et al . Hornerssyndrome and thyroid neoplasms.ORL J Otorhinolaryngol Relat Spec 2002;64 :4952.

44. Lin CC, Tsan KW, Chen PJ. The relationship betweensleep apnea syndrome and hypothyroidism.Chest 1992;102 :16637.

45. Ajlouni KM, Ahmad AT, El-Zaheri MM,et al .Sleepwalking associated with hyperthyroidism.Endocr Pract 2005;11 :510.

46. DeLong GR. Effects of nutrition on braindevelopment in humans.Am J Clin Nutr 1993;57 (Suppl 2):286S290S.

47. Bargagna S, Canepa G, Costagli C,et al .Neuropsychological follow-up in early-treatedcongenital hypothyroidism: a problem-oriented

approach. Thyroid 2000;10 :2439.48. Volpe R. Rational use of thyroid function tests.Crit

Rev Clin Lab Sci 1997;34 :40538.49. Campbell WW, DeJong RN, Haerer EF.DeJongs the

neurologic examination: incorporating the fundamentals of neuroanatomy and neurophysiology . Lippincott Williams & Wilkins,2005.

Practical Neurology

thyroid and neurology

Documents