the pattern approach to logic diagnosis

8/14/2019 The Pattern Approach to logic Diagnosis

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Clinicians are sometimes

surprised when they re-

fer an animal with a der-

matologic problem to a specialist

who rapidly compiles a list of dif-

ferential diagnoses and pinpoints

specific tests to be performed.

There is nothing magical about

the dermatologists action! Al-

though dermatologists routinely

see various cutaneous lesions, it

is their ability to properly identifythese lesions that provides the

critical information necessary to

compile a list of diagnostic differ-

entials and select appropriate

testing.

Key to making a diagnosis

and treating a previously unseen

dermatologic problem is keep-

ing an open mind to the possi-

bility of a novel diagnosis and

starting with the usual history

taking. After a very thoroughhistory, the basic morphology

of cutaneous lesions must be

reviewed. Then, the predomi-

nant pattern of lesions should

be determined and the same al-

gorithmic approach used for

any other problem followed.

To make a correct dermato-

logic diagnosis, clinicians must

first be able to recognize prima-

ry and secondary lesions and

be able to associate them with a

predominant morphologic pat-

tern. This column focuses on

the evidence that clinicians can

seeduring a clinical examina-

tion; this evidence is coupled

with the patient history to nar-

row the diagnostic possibilities.

Although seemingly easy,

correctly describing a skin con-dition can be quite difficult. To

do pattern diagnosis effectively,

descriptions must be precise

and accurate. Differentiating a

scale from crust or a papule

from a plaque, for example, is

critical. Without a correct de-

scription of the morphologic

pattern, accurate diagnosis is

usually impossible. Table One

provides an easy-to-use list of

lesions, their descriptions, andthe morphologic pattern associ-

ated with each. In summary,

approaching each case in three

distinct steps will allow the clin-

ician to make a correct diagno-

sis in most cases (see the box).

Determine Pattern

Using your knowledge of pri-mary and secondary lesions,

carefully evaluate the animal to

determine the predominant pat-

tern. This is done by asking a se-

ries of questions in a specific or-

der (see the algorithm). Always

select the predominant pattern. A

dog with profound scaling and

three pustules does not have a

vesiculopustular disorder; it has

The Compendium September 1996 Small Animal

tables provided here (Tables Two

through Nine). Making such a list

not only increases your aware-

ness of possible dermatologic

conditions but provides an ex-

tremely helpful reference that

can accompany samples submit-ted for diagnostic testing (espe-

cially biopsies for histopathologic

assessment).

Perform DiagnosticTesting

With a pattern diagnosis and

differential diagnostic list, the

possible diagnoses can be nar-

rowed. With experience, it is

The Pattern Approach toDermatologic Diagnosis

PERSPECTIVES IN VETERINARY MEDICINE

Lowell Ackerman, DVM, PhDDiplomate, ACVD

Dermvet Inc.Scottsdale, Arizona

an exfoliative dermatosis. A cat

with a large, hairless mass on its

back has a papulonodular der-matosis, not alopecia. There are

eight major categories of pre-

dominant patterns.

Formulate DifferentialDiagnostic List

Once you have determined the

fit between your case and one of

the eight major categories, you

can create a comprehensive dif-

ferential diagnostic list from the

possible to prioritize the most

likely diagnoses and perform

tests accordingly. At first, how-ever, information in Table Ten

can be used to create a mini-

mum data base, which will reveal

the most common condition as-

sociated with a particular presen-

tation. If the minimum data base

does not suggest a diagnosis,

proceed to the next step col-

umn in Table Ten. By following

this approach, a diagnosis can

be made in most cases.

s Most dermatologic problems have a characteris-tic clinical presentation.

s A differential diagnostic list can often be madeby assigning clinical cases into one of eightmajor categories of predominant lesion patterns.

s Deciding which diagnostic tests to performbecomes more routine if the lesions have beengrouped into one of the eight major categories.

KEYPOINTS

V

How To Make a CorrectDermatologic Diagnosis

Step 1 Determine pattern.Step 2 Formulate differential diagnostic list.Step 3 Perform diagnostic testing.


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Small Animal The Compendium September 1996

KeyDescriptionof

lesions

Predominantlesi

onpatterns

InitialAlgorithm

n

o

no

no

no

no

no

no

no

yes

yes

yes

yes

yes

yes

yes

yes

yes

no

Primarypigmentary

changes?

Raisedlesions?

Flat,depressed,ormildly

elevatedlesions?

Flu

id-filledlesions?

Solidandraisedlesions?

Hairlossprominent?

Reevaluatepattern

Reevaluate

pattern

Breaksinep

ithelial

integrity?

Scalingprominent? S

kinthickened

?

Pigmented

lesionsand

dermatoses

Vesiculopu

stular

dermato

ses

Papulonodular

dermatoses

Alo

pecic

derm

atoses

Erosive-

ulcerative

dermatoses

Exfoliative

der

matoses

Indurated

dermatoses

M

aculopapular

dermatoses


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TABLE ONE

Pattern Diagnosis

Lesion Description Pattern Association

Macule A circumscribed, flat discoloration of the skin up to

1 cm in diameter

Maculopapular

PigmentedPatch Macules >1 cm Maculopapular

Pigmented

Papule A circumscribed, elevated, superficial, solid lesionup to 1 cm in diameter

Maculopapular

Plaque A circumscribed, elevated, superficial, solid lesion>1 cm; a papule that has enlarged in two dimensions

Papulonodular (plaque)

Wheal An edematous, transitory papule or plaque Papulonodular (plaque)Indurated (turgid)

Nodule A solid lesion with depth; a papule that has enlargedin three dimensions

Papulonodular (nodule)

Vesicle A circumscribed elevation of the skin up to 1 cm indiameter and containing serous fluid

Vesiculopustular

Bulla A vesicle >1 cm in diameter Vesiculopustular

Pustule A circumscribed elevation of the skin containingpurulent fluid

Vesiculopustular

Epidermal collarette A circular peeling rim of scale Vesiculopustular

Petechia A circumscribed deposit of blood or blood pigmentup to 1 cm in diameter

Pigmented (red)

Purpura A circumscribed deposit of blood or blood pigment>1 cm in diameter

Pigmented (red)

Crust Variously colored collections of skin exudates Erosive-ulcerative

Excoriation Abrasion of the skin, usually superficial andtraumatic in origin

Maculopapular

Fissure A linear break in the skin that is sharply definedwith abrupt walls

MaculopapularPapulonodularExfoliative

Erosion An excavation in the skin limited to the epidermisand not breaking the integrity of thedermoepidermal junction

Erosive-ulcerative

Ulcer An irregularly sized and shaped cavitation in the

skin extending into the dermis

Erosive-ulcerative

Scar A formation of connective tissue replacing tissuelost through injury or disease

Indurated

Lichenification A diffuse area of thickening and scaling, withresultant increase in the skin lines and markings

MaculopapularInduratedExfoliative

Scale Shedding dead epidermal cells that may be dry orgreasy

ExfoliativeMaculopapular

Induration Palpable thickening of the skin Indurated

Sclerosis Hardening of the skin Indurated

Hyperpigmentation Darkening of the skin Pigmented (dark)Maculopapular


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Red Drug eruption Drug eruptionPetechiae PetechiaePurpura PurpuraVasculitis VasculitisContact dermatoses Contact dermatosesLupus erythematosus Lupus erythematosusPhotodermatitis PhotodermatitisErythema multiforme Erythema multiformeSkin-fold pyoderma Eosinophilic plaquePyotraumatic dermatitis Linear granulomaHistiocytomaDemodicosisFlushing syndrome

Lyme borreliosisHookworm dermatitis

White Lupus erythematosus Lupus erythematosus(depigmented) Albinism Albinism

Uveodermatologic syndrome Waardenburg-Klein syndromeMorphea Chdiak-Higashi syndromeVitiligo Periocular leukotrichiaTyrosinase deficiency

Dark Basal-cell tumor Basal-cell tumorMelanoma MelanomaPostinflammatory change Postinflammatory change

HypothyroidismHyperadrenocorticismGrowth hormoneresponsive dermatosis

Acanthosis nigricansAdrenal sex-hormone dermatosisLentiginesVascular neviHemangiomaHemangiosarcomaOrganoid nevusMelanocytic nevusMelanoderma and alopecia

Skin-colored Epidermal nevus Epidermal nevusScar ScarPapillomaMorpheaSebaceous-gland hyperplasiaCallusSebaceous nevus

Other Dalmatian bronzing syndrome XanthomatosisAcquired aurotrichia Waardenburg-Klein syndromeTyrosinase deficiency Chdiak-Higashi syndrome

Waardenburg-Klein syndrome

TABLE TWO

Differential Diagnosis for Pigmented Lesions

Category Canine Feline


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Vesicular Pemphigus PemphigusPemphigoid PemphigoidErythema multiforme Lupus erythematosusDermatomyositis Epidermolysis bullosaEpidermolysis bullosa Cat pox infectionDermatitis herpetiformisMucinosisIdiopathic ulcerative dermatosis

Pustular Demodicosis DemodicosisBacterial pyoderma Bacterial pyodermaDermatophytosis DermatophytosisSubcorneal pustular dermatosis AbscessSterile eosinophilic pustulosis AcneLupus erythematosus Lupus erythematosus

Acne FIV infectionLinear IgA dermatosis Adverse food reactions

Adverse food reactionsPemphigus

TABLE THREEDifferential Diagnosis for Vesiculopustular Lesions


Nodular Parasitoses Abscess

Deep pyoderma AcneAtypical pyoderma Atypical pyodermaDermatophytosis DermatophytosisIntermediate mycoses Intermediate mycosesDeep mycoses Deep mycosesLupus profundus ParasitosesNeoplastic NeoplasticDermoid cyst Dermoid cystNodular panniculitis Nodular panniculitis

Juvenile cellulitis Lupus profundusMucinosis XanthomaEosinophilic granuloma Eosinophilic granulomaSebaceous adenitis Leprosy

Sterile pyogranuloma Opportunistic mycobacteriaOpportunistic mycobacteriaAcral pruritic noduleCalcinosis circumscriptaNodular fasciitisProtothecosisDracunculiasis

Plaques Dermatophytosis DermatophytosisUrticaria UrticariaLymphoma LymphomaBacterial hypersensitivity Sporotrichosis

TABLE FOUR

Differential Diagnosis for Papulonodular Lesions



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Lupus profundus Eosinophilic plaqueViral papillomatosis Mast-cell tumor

Calcinosis cutis Linear granulomaCalcinosis circumscripta Vitamin E deficiency Histiocytoma MucopolysaccharidosisHistiocytosis XanthomatosisKeratoses Tumoral calcinosisNevi NeviLichenoid dermatoses Lichenoid dermatosesMucinosis Erythema multiformeErythema multiforme Papillomavirus infection

Acanthosis nigricans Perforating dermatitisDermatitis herpetiformisUrticaria pigmentosa

Acral lick dermatitis

Malasseziadermatitis

Vegetative Mast-cell tumor Mast-cell tumorCutaneous papilloma Squamous-cell carcinomaFibroma FibromaNevi NeviSebaceous gland hyperplasiaTransmissible venereal tumorPemphigus vegetans

TABLE FOUR (continued)


Plaques (continued)

Focal/multifocal Demodicosis DemodicosisBacterial pyoderma Bacterial pyodermaDermatophytosis Dermatophytosis

Alopecia areata Alopecia areataCutaneous asthenia Cutaneous astheniaTraction alopecia Traction alopeciaMorphea Injection site reactionInjection site reaction Cicatricial alopeciaCicatricial alopecia

Patchy Demodicosis DemodicosisCheyletiellosis CheyletiellosisLice infestation Lice infestationDermatophytosis DermatophytosisBacterial pyoderma Drug eruptionLupus erythematosus Lupus erythematosusTelogen defluxion Telogen defluxionProtein deficiency HyperadrenocorticismDrug eruptionSebaceous adenitisBronzing syndromeColor-mutant alopecia

TABLE FIVE

Differential Diagnosis for AlopeciaCategory Canine Feline


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SpiculosisLeishmaniasisFamilial benign pemphigus

Regional Discoid lupus erythematosus Discoid lupus erythematosusHypothyroidism Endocrine alopeciaHyperadrenocorticism HyperadrenocorticismGrowth hormoneresponsive dermatosis Psychogenic alopecia

Adrenal sex-hormone dermatosis Postclipping alopeciaSeasonal flank alopecia Pinnal alopeciaHyperestrogenism Preauricular alopeciaHypoestrogenism Acquired symmetric alopeciaPattern baldness Pancreatic paraneoplastic alopeciaTesticular neoplasia

DermatomyositisFollicular dysplasiaToxicity (e.g., thallium)Postclipping alopeciaPinnal alopeciaBenign familiar chronic pemphigusMelanoderma and alopecia

Waterline disease

Generalized Dermatophytosis DermatophytosisLupus erythematosus Lupus erythematosusDrug eruption Drug eruptionDemodicosis Alopecia universalis

Hypotrichosis HypotrichosisTelogen defluxion Telogen defluxionPostclipping alopecia

TABLE FIVE (continued)


Patchy(continued)

Parasitic Fleas FleasDemodicosis DemodicosisSarcoptic mange Notoedric mange

Leishmaniasis

Microbial Skin-fold pyoderma Superficial pyodermaPyotraumatic dermatitis Systemic mycosesPerianal fistulae Cat pox infectionBacterial granuloma Bacterial granulomaMycetoma MycetomaOpportunistic mycobacteriosis Opportunistic mycobacteriosisSepticemia/toxemia Septicemia/toxemiaDermatophilosis DermatophilosisCandidiasis FIV infection

Sporotrichosis

TABLE SIX

Differential Diagnosis of Erosive-Ulcerative Lesions



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Immune-mediated Pemphigus PemphigusPemphigoid Pemphigoid

Cutaneous vasculitis Cutaneous vasculitisToxic epidermal necrolysis Toxic epidermal necrolysisDrug eruption Drug eruptionLupus erythematosus Lupus erythematosusLupoid dermatosis Erythema multiforme majorDermatomyositisErythema multiforme major

Congenital-hereditary Cutaneous asthenia Epidermolysis bullosaEpitheliogenesis imperfecta Cutaneous astheniaEctodermal defect Ectodermal defectDermatomyositisFamilial benign pemphigus

Familial vasculopathyEpidermolysis bullosa

Acrodermatitis

Miscellaneous Vesiculopustular dermatoses Indolent ulcerThallium toxicosis Bowens diseaseBurn Squamous-cell carcinomaContact eruption HyperadrenocorticismCutaneous T-cell lymphoma Vesiculopustular dermatosesMetabolic dermatoses BurnIdiopathic erosive dermatosis Contact eruption

Acquired skin fragility

TABLE SIX (continued)


Patchy Ectoparasitism EctoparasitismDermatophytosis DermatophytosisDrug eruption Drug eruptionPemphigus foliaceus Pemphigus foliaceusFatty acid deficiency Fatty acid deficiency T-cell lymphoma Protein deficiency Pagetoid reticulosis Vitamin A deficiency

Sjgrens syndrome Vitamin E deficiency Hyperestrogenism Biotin deficiency Vitamin Aresponsive dermatosis LynxacariasisSebaceous adenitis Adverse food reactionsGeneric dog food disease Perforating dermatitisSubcorneal pustular dermatosisChronic maculopapular dermatosesParapsoriasis

Adverse food reactionsHypothyroidismLupoid dermatosisLeishmaniasis

TABLE SEVEN

Differential Diagnosis for Exfoliative Lesions



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Regional Pemphigus foliaceus Pemphigus foliaceusPemphigus erythematosus Pemphigus erythematosus

Discoid lupus erythematosus Discoid lupus erythematosusHypothyroidism CheyletiellosisZinc-responsive dermatosisTyrosinemiaNasodigital hyperkeratosisLeishmaniasisMalasseziadermatitis

Generalized Dermatophytosis DermatophytosisDrug eruption Drug eruptionSystemic lupus erythematosus Systemic lupus erythematosusPemphigus foliaceus Pemphigus foliaceusKeratinization disorders Keratinization disordersDemodicosis CheyletiellosisHypothyroidism Hypereosinophilic syndromeVitamin E deficiency LynxacariasisIchthyosis T-cell lymphomaT-cell lymphoma Metabolic disordersMetabolic disordersLeishmaniasisGraft-versus-host disease

TABLE SEVEN (continued)


Turgid Urticaria UrticariaAngioedema AngioedemaMyxedema Growth hormonesecreting tumor

Juvenile cellulitis MucopolysaccharidosisMucinosis Relapsing polychondritisNephrotic syndrome Plasma cell pododermatitisUrticaria pigmentosaHookworm dermatitis

Solid Cellulitis CellulitisBacterial granuloma Bacterial granulomaFungal granuloma Fungal granulomaCalcinosis cutis Calcinosis cutisTumoral calcinosis ScarScar NeoplasiaNeoplasia Amyloidosis

Amyloidosis Intermediate mycosisScleroderma Chronic maculopapular dermatitisChronic maculopapular dermatosesSebaceous adenitis

TABLE EIGHTDifferential Diagnosis of Indurated Lesions



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Macular Allergic inhalant dermatitis Allergic inhalant dermatitisFood allergy Food allergy Allergic contact dermatitis Allergic contact dermatitisIrritant contact dermatitis Irritant contact dermatitisDrug eruption Drug eruptionBacterial pyoderma Erythema multiformeLupus erythematosus Endoparasite infectionErythema multiforme Ectoparasite infestation

Alopecia areata Lupus erythematosusEndoparasite infection Alopecia areataEctoparasite infestation

Acanthosis nigricans

Papular Parasitic dermatoses Miliary dermatitisVitamin Aresponsive dermatosis Parasitic dermatosesBacterial folliculitis Bacterial folliculitisDrug eruption Drug eruptionFood allergy Food allergy Dermatophytosis DermatophytosisComedones/acne Comedones/acneErythema multiforme Erythema multiformeHormonal hypersensitivity Hypereosinophilic syndromeDermatitis herpetiformis

TABLE NINE

Differential Diagnosis of Maculopapular Lesions


Pigmented Histopathology As per biopsies

Vesiculopustular Skin scrapings Histopathology Cytology (e.g., impression smear) Cultures

Papulonodular Skin scrapings As per results of minimumCytology (e.g., fine-needle aspirate) data base testsHistopathology Culture tests

AlopecicFocal Skin scrapings Histopathology

Culture for dermatophytesTrichogram

Widespread Skin scrapings Endocrine profilesCulture for dermatophytes Histopathology TrichogramComplete blood countBiochemistriesUrinalysis

Erosive-ulcerative Skin scrapings Histopathology Cytology (e.g., impression smear)

TABLE TEN

Step-by-Step Approach to DiagnosisClassification Minimum Data Base Next Step


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Figure 1A dog with regional (nasal) alopecia and associatedexfoliative dermatosis. The most likely clinical diagnoses werelupus erythematosus (systemic or discoid), pemphigus (foli-aceus or erythematosus), dermatomyositis, zinc-responsivedermatosis, and follicular dysplasia. Minimum data base con-sisted of skin scrapings, culture for dermatophytes, completeblood count, routine biochemistry, and a trichogram. Onlythe trichogram showed abnormalities, with telogen hairs pre-dominating. Biopsies were then taken and histopathologicanalysis confirmed the diagnosis as dermatomyositis.


Exfoliative Skin scrapings Histopathology Complete blood count Endocrine profileBiochemistriesUrinalysisFungal culture

InduratedTurgid Complete blood count Histopathology

BiochemistriesUrinalysisFecal tests

Solid Cytology (e.g., fine-needle aspirate) Complete blood countHistopathology Biochemistries

Cultures

Maculopapular Skin scrapings Dietary trialComplete blood count Allergy testingFecal tests Cultures

Histopathology

TABLE TEN (continued)

Classification Minimum Data Base Next Step

Figure 2 A cat with an erosive-ulcerative dermatosis. Themost likely clinical diagnoses were hypersensitivity disorders,parasites, microbial infections, and immune-mediated der-matoses. Minimum data base consisted of skin scrapings andimpression smears. The skin scrapings were negative, but cy-tologic preparations revealed a mixed inflammatory cell popu-lation of neutrophils, eosinophils, and histiocytes; few mi-crobes were present. Hypersensitivity conditions wereconsidered and a food trial confirmed a hypersensitivity tobeef.


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AcknowledgmentAll photographs in this article are from Nesbitt GH, Ackerman LJ (eds): Dermatolo-

gy for the Small Animal Practitioner. Trenton, NJ, Veterinary Learning Systems, 1991,

Plates I, III, VI, VIII, IX, and X.

Figure 3A cat with an exfoliative dermatosis that is most prominent over thetop of the head. Minimum data base consisted of skin scrapings and cytologicpreparations (impression smears and acetate-tape impressions). The skin scraping

was positive for Notoedres cati.

Figure 5A dog with dermal nodules and plaques (a papulonodular dermatosis).Minimum data base consisted of skin scrapings, cytologic preparations (fine-nee-dle aspiration), and biopsies for histopathologic analysis. The cytologic prepara-tions revealed a mononuclear population of cells, which were presumed to besmall lymphocytes. The histopathologic assessment confirmed the diagnosis ascutaneous lymphoma.

Figure 4A dog with regional alopecia and associated hyperpigmentation. Mini-mum data base included skin scrapings, culture for dermatophytes, a trichogram,complete blood count, biochemistries, and urinalysis. The trichogram revealedthat telogen hairs predominated. The only other abnormality was an increasedserum alkaline phosphatase level. Endocrine profiles confirmed a diagnosis of pi-tuitary-dependent hyperadrenocorticism.

Figure 6A dog with axillary hyperpigmentation (a pigmented dermatosis).Minimum data base consisted of biopsies for histopathologic assessment. The di-agnosis was acanthosis nigricans.

Figure 7A cat with an indurated (solid) and erosive-ulcerative dermatosis. Min-imum data base included cytologic preparations (fine-needle aspiration and im-pression smears) and biopsies for histopathologic analysis. The cytologic prepara-tions revealed a pyogranulomatous infiltrate with histiocytes and giant cells. Thehistopathologic assessment confirmed the diagnosis as nocardiosis. The cat hadconcomitant FIV infection.

the pattern approach to logic diagnosis

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