DX Tests For Derm Flashcards
“The basics”
Skin scrapings
Flea combing /coat collection
Trichogram
Cytological exam
Bacterial culture & sensitivity
Wood’s lamp exam
Fungal culture
Skin biopsy
Skin scrapings
ID of ectoparasites are key
Sarcoptes
Demodex
Notoedres
Cheyletiella
Otodectes cyanotis
Trombicula
Importance for collecting Demodex canis
Living deeper in hair follicle under skin, this requires deeper scrapings or pressure. Capillary bleeding should occur
Sarcoptes, cheyletiella and deodex gatoi scraping
Broader scrapes or superficial
Magnification for skin scrapings
Low power, 4-10x magnification
Trichogram
ID for cheyletiella, Demodex and lice
Useful for diagnosing Dermatophytosis
Confirming pruritic condition
ID hair growth stage
Cytological exam
Useful for DX tools for
Pyoderma
Malassezia dermatitis
Otitis externa
Skin neoplasia
Inflammatory disease
Cytological exam - swab smear
Ears, exudative & moist lesions
Nail beds/folds
Impression smear is ideal for
Surface of intact exudative lesions
After lancing papules or pustules
Following crust removal
Scotch tape prep
Ideal for dry and waxy lesions
Lesions difficult to reach w a slide - toes etc
Fine needle aspiration
20-22 gauge with a 6-12 cc syringe
Used for nodules, tumor
Plaque or abscess
caution w suspected mast cell tumors
Yeast in Cytological exam
Malassezia pachydermatis
3-5um (comparable size to RBC)
0.5-1 yeast /oil immersion field is significant is taken from effected sight
Bacteria for Cytological exam
S. Pseudointermedius - most common
0.5-1.5um in size cocci
Normal in ears & skin, common w degenerate neutrophils
Pseudomonas Aeruginosa - cytology
Common in ear samples - always pathologic
High incidence of antibiotic resistance
Mycobacteria in cytology
Acid fast stains is ideal
Simonsiella - very large rods, 2-3mm wide
Inhabitants of the oral cavity, non pathologic
On skin, associated w licking
Fungal organisms - cytology
Dermatophyte spores
Subcutaneous & deep fungal organisms: cryptococcus, coccidioides, blastomycosis, sporotrichosis, histoplasmosis, phaeohyphomycosis, zygomycosis
Inflammatory cells found on cytology
Neutrophils - degenerate, intracellular bacteria: pyoderma
Non-degenerate, no bacteria: pemphigus foliaceus, primary allergic reaction, irritant reaction
Inflammatory cells - eosinophils
Parasitic disease
Hypersensitivity
Foreign body reaction - free keratin in dermis
Eosinophilic disease complex
Pemphigus foliaceus
Mast cell tumors
Sterile eosinophilic disease
Monocyte inflammatory cells
Macrophages, lymphocytes
More chronic & deeper lesions
Macrophages markedly vacuolated & degenerated
Acid-fast for mycobacteria, grocotts methenamine silver (GMS) stain for fungal elements
Culture if degenerate neutrophils & no organisms
Mast cells inflammatory cells
Sparse, parasitic, allergic diseases
High numbers = mast cell tumors
Epithelial cells on cytology
Corneocytes (non-nucleated)
Keratinocytes (nucleated)
From surface skin samples, suggest parakeratosis (abnormal turnover, erosions)
Easy to confuse keratohyalin granules or melanin granules w bacteria
Corneocytes appearence on stain
Often roll up into tube shaped structures which tend to stain dark purple
Bacterial culture & sensitivity
Used for DX of pyoderma, otitis media/interna
These tests are important for antibiotic selection
*rod shaped bacteria are seen on skin/ear cytology
Good for intact pustules, epidermal collarettes, draining tracts, purulent discharge in ear canals
Tissue culture for bacterial /fungal in skin
Plaques, nodular lesions, fistulous tracts
*disinfect skin, take biopsy, remove epidermis, culture for aerobic/anaerobic
Woods lamp exam
Good for diagnosing Dermatophytosis
Affected hairs fluoresce APPLE GREEN
Individual hair shafts fluoresce
Scales/crust do not light up
False +/- woods lamp exam
False negative: 50% of microsporum canis
Not all affected areas will exhibit fluorescence
Iodine destroys fluorescence
False positive: keratin, soap, petroleum, bacteria will fluoresce but not bright green
Fungal culture
Most sensitive method for diagnosing Dermatophytosis
Dermatophyte test medium (DTM)
Sabourauds dextrose agar
Cycloheximide (antifungal)
Gentamicin & chlortetracycline (antibacterial)
Phenol red (pH indicator)
Fungal culture
Florescent hairs, broken hairs, scales & crusts are collected from lesion sites
Mackenzie brush technique to detect the asymptomatic carriers - sterile toothbrush
Comb whole body for 2-3 minutes
Incubate at 25-28*c for 3-4 weeks
