olfactory dysfunction and disorders
TRANSCRIPT
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Olfactory Dysfunction and
Disorders
Jing Shen, M.D.
Faculty Advisor: Matthew Ryan, M.D.
The University of Texas Medical Branch
Department of Otolaryngology
Grand Rounds Presentation
November 26, 2003
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Introduction
Importance of olfaction:
Determines the flavor of foods and beverages
Early warning system for detection of
environmental hazards.
Prevalence:
2 million Americans
At least 1% population under age of 65 and well over 50% over age 65
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Anatomy and Physiology
3 neural systems
CN I: main olfactory system
Mediates odor sensation
CN V: trigeminal somatosensory system
Mediates somatosensory sensation
CN 0: nervus terminalis
Unknown exact function in humans
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Olfactory Epithelium
Pseudostratified columnar epithelium
Located in the upper recesses of the nasal chambers
Cribriform plate, superior turbinate, superior septum, section of middle turbinate
Harbors sensory receptors of CN I
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Cell Types in Olfactory Epithelium
Bipolar sensory receptor neurons
6,000,000 cells in adults
Olfactory receptors located on the ciliated dendritic ends
Axons form 40 bundles as olfactory fila
Microvillar cells
Near the surface of epithelium
Exact function unknown
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Cell Types
Supporting cells
Insulate receptor cells
Regulate mucus composition
Deactivate odorants
Protect epithelium from foreign agents
Globose basal cells
Horizontal basal cells
Cells lining Bowman’s gland
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Olfactory Neuroepithelium
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Olfactory Sensory Receptor Neuron
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Receptors
Located on cilia of receptor cells
1000 classes - 1% of all expressed genes
Linked to guanine nucleotide binding protein->activate adenylate cyclase-> cAMP->depolarization
One cell- one type of receptor
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Olfactory Bulb
Located on top of cribriform plate at the base of frontal lobe
Complex processing center
Receives receptor cell axons
Olfactory tract projects to olfactory cortex
Frontal lobe, temporal lobe, thalamus, hypothalamus
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Classification of Olfactory Disorders
Anosmia: absence of smell sensation
Partial anosmia: ability to perceive some, but not all, odorants
Hyposmia: decreased sensitivity to odorants
Hyperosmia: abnormally acute smell function
Dysosmia: distorted smell perception
Phantosmia: olfactory hallucination
Olfactory agnosia: inability to recognize an odor
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Classification
Conductive loss
Obstruction of nasal passages
E.g., chronic nasal inflammation, polyposis
Sensorineural loss
Damage to neuroepithelium
E.g., viral infection, airborne toxin
Central olfactory neural loss
CNS damage
E.g., tumors, neurodegenerative disorders
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Evaluation and Diagnosis
History: most important Olfactory ability prior to the loss
Antecedent events (head trauma, URI)
Severity
Onset (gradual vs. acute)
Pattern
Other medical conditions
Nasal sinus disease and allergy
Previous surgery
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History (cont)
Medications
Smoking history
Occupational history
Any complaint of taste loss
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Evaulation and Diagnosis
Physical exam:
Nasal endoscopy
Neurological exam
Laboratory tests:
Suggested by history and PE only
Radiographic Imaging:
CT: nasal and sinus disease
MRI: intracranial causes
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Evaluation and Diagnosis
University of Pennsylvania Smell Identification Test (UPSIT) 4 booklets of 10 microencapsulated
odors
Scratch and sniff format
Four responses accompanying each odor
Forced choice design
Scores are compared to norms (sex- and age-related)
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UPSIT (cont)
Scores classified into:
Normal 36-40
Partial anosmia 20-35
Total anosmia 8-15
Probable malingering 0-5
Reliability is very high
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Post Upper Respiratory Infection
Sensorineural loss
The most frequent cause of smell loss in adults
More common in middle or older age group
Woman>man
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Post URI
History:
follows a viral-like URI, usually more severe than usual
Loss is most commonly partial
Occasionally with dysosmia or phantosmia
PE: unremarkable
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Post URI
Mechanism: unclear Direct insult to neuroepithelium
Greatly reduced number of olfactory receptors
Dendrites do not reach surface
Lack sensory cilia
Replacement of sensory epithelium with respiratory epithelium
Ascends to the olfactory tracts or bulbs
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Post Viral Olfactory Disorder
Olfactory cells decreased in number
Two cilia on olfactory vesicle
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Post URI
Worst case: severe destruction, no regeneration -> anosmia
Mild case:
patchy destruction -> hyposmia
Complete regeneration -> normosmia
Patchy regeneration or faulty regeneration -> dysosmia
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Post URI
Treatment: no effective treatment
Prognosis:
Complete recovery in 3 weeks or permanent dysfunction
Meaningful recovery is rare
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Head injury
Incidence:
4-7% in early studies
Reaching 50% in recent studies
Generally associated with the severity of the injury
Heywood (1990) matched GCS with olfactory test scores
Lower GCS score, higher percentage of patients with olfactory impairment
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Head Injury
Mechanism: Sinonasal tract alteration
Direct injury to olfactory epithelium (mucosal edema, hematoma)
Nasal skeleton fracture
Post-traumatic rhinosinusitis
Potentially treatable
Shearing injury
Tearing or shearing the axons
With naso-orbito-ethmoid region fracture
Translational shifts in the brain secondary to coup or contracoup forces
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Head Injury
Mechanism (con):
Brain contusion or hemorrhage
Treatment:
Irreversible most of time
Prognosis worsen with time
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Post Traumatic Injury
Olfactory cells decreased in number
Olfactory receptor is aciliate
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Nasal and Sinus Disorders
Traditionally viewed as conductive loss
Airflow blockage caused by rhinosinusitis prevent odorant molecules from reaching epithelium
Surgery or medical treatment alone not effective
Defining factor may be the severity of the histopathological change
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Nasal and Sinus disorder
Doty and Mishra (2001): Degree of olfactory loss is associated with the
severity of nasal sinus disease
Improve with systemic steroid and topical steroid
No documented relationship between olfactory test scores and intranasal airway access factors
Chronic inflammation may be toxic to olfactory mucosa
Thin, atrophic epithelium
Respiratory epithelium replaces sensory epithelium
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Nasal and Sinus Disorder
Doty and Mishra (2001)
Septoplaty and rhinoplasty do not have long-term deleterious effect
Improvement of olfactory function postoperatively with sinus surgery (incomplete)
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Other Causes of Olfactory Disorders
Toxin
Tumor
Congenital
Endocrine
Psychiatric
Neurodegenerative disorder (Parkinson, Alzheimer disease)
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Treatment of Olfactory Disorder
Conductive loss: relieve obstruction
Allergy management
Topical cromolyn
Topical and systemic corticosteroids
Surgical procedure
Sensorineural loss: no effective treatment
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Bibilography McCaffrey, Thomas V.: Rhinologic diagnosis and
treatment. New York, Thieme,1997, p5, 10, 16. Doty, Richard: Handbook of Olfaction and Gustation.
New York, Marcel Dekker, Inc. 2003, pp 461-473. Doty R, Anupam M. Olfaction and its alteration by nasal
obstruction, rhinitis, and rhinosinusitis. Laryngoscope 2001, 111:409-423
Bailey et.al., Head and neck surgery- otolaryngology. NewYork, Lippincort Williams and Wilkins. 2001, pp 247-259.
Sobol S, Frenkiel S. Olfactory dysfunction. Canadian Journal of Diagnosis. 2002, august pp2-12.