Dermatology - Diagnostic Tests Flashcards
When are skin scrapes performed?
When you suspect a parasitic infection
Describe skin scrape technique for demodex canis versus for sarcoptes spp., cheyletiella spp., demodex gatoi:
- Select site affected by disease, but avoid traumatized areas
- scrape with spatula or blade covered in mineral oil
- Demodex canis -> live deep within the skin –> require you to squeeze the skin * scrape deeply
- sarcoptes spp., cheyletiella spp., demodex gatoi –> broad, SF scrapings
- transfer onto glass slide + cover slip
- examine @ low power (4x to 10x)
- keep light condenser on low to enhance contrast & shadows
Sarcoptes scabei
Cheyletiella spp.
Demodex gatoi
Demodex canis
Sequela of dermal allergic reaction?
E.g., flea bite
Pruitis
Trichogram – uses
Visulaize hair follicale itself (the shaft, bulbs, etc.) to either support or prove your dx
- Identiy ectoparasites (cheyletiella spp., demodex spp., lice); identify anagen versus telogen hair growth; identidy hair shaft defects
- Support dermatophytosis dx
- Confirm pruritic condition
Broken hair shaft –> contributing to cat’s alopecic lesion
Dense areas of melanin = color dilution alopecia.
Uses of cytological examination? What regions of the body are more difficult to obtain cytologic samples?
Dry regions of skin – do tape test instead
What type of lesion is ideal for an impression smear?
**surface of intact, exudative/purulent (wet lesions) (mucous membrane, abscess)
What should you administer to a patient before FNA of a possible mast cell, and why?
Diphenhydramine — if a mast cell, FNA can induce degranulation –> patient can undergo anaphylactic shock!
A mast cell is a type of white blood cell that is found in many tissues of the body. Mast cells are allergy cells and play a role in the allergic response. When exposed to allergens (substances that stimulate allergies), mast cells release chemicals and compounds, a process called degranulation. One of these compounds is histamine. Histamine is most commonly known for causing itchiness, sneezing, and runny eyes and nose – the common symptoms of allergies. But when histamine (and the other compounds) are released in excessive amounts (with mass degranulation), they can cause full-body effects, including anaphylaxis, a serious, life-threatening allergic reaction.
What areas of the body should you use a swab smear for cytological sample?
Ears- exudative, moist, purulent skin lesions. Nail bed folds.
When to use scotch tape prep slide
Dry, waxy lesions; lesions that are difficult to reachw ith microscope slide
Importance of heat-fixing specimen onto slide?
If sample is oily/waxy, they can get “washed off” in the diff quick stain process (alcohol-based liquids) = loss of sample!
Signigicant finding of yeast of sample taken from inflammed skin or ear? Most common yeast?
0.5-1 yeast per oil field
most common = Malassezia pachydermatitis
What organism is a normal flora of the ears and skin, but is associated with degenerative neutrophils in infection?
Staphylococcus pseudointermedius
What organism is typically pathognomic when rod-shape, long, short chains are visualized from ear samples? What is it typically indicative of?
Pseudomonas aeruginosa – indicative of abx resistance
Staining method for mycobacteria
Acid-fast stain
What types of inflammatory cells may be picked up on cytological examination?
- Degeneratie neutrophils with bacteria (pyoderma)
- Non-degenerate neutrophils with no bacteria (allergic reaction, irritant rxn, pemphigus foliaceus)
- Eosinohpils (parasistic disease, hypersensitivity, FB action, MCTs, etc.)
- MØ (marledly vacuolated & degenerate, Lymphocytes
- Mast Cells
Keratinocytes
Nucleated epithelial cells; don’t confuse with melanin granules
collected from surface skin samples
Corneocytes
Non-nucleated epithelial cells
When to use bacterial culture & sensitivity
Diagnosis of pyoderma; otitis media/interna
Factors determining how to select the appropriate ABX for dermatologic infection?
When to perform a tissue culture for a bactieral or fungal skin infection?
Plaques, nodular lesions, fistulous tracts, deep pyodermas
Draining tract: culture it if you don’t know what the draining is coming form / to determine if an ABX will be susceptible to it
Steps of punch biopsy
- Prep area (clip, aspectic prep)
- Aseptic technique (sterile gloves, sterile equipment, etc.)
- Use scalpel to trim away epidermal layer
- Submit for culture
What condition is a Wood’s Lamp Examination used for?
Dermatophytosis (ring worm)
Some cases: dead skin cells will fluoresce right around edge of lesion
What organisms can cause the Wood’s lamp examination to show fasle negatives and false positives?
Wood’s Lamp Examination – Mircosporum canis
Wood’s Lamp Examination – Mircosporum canis
A 4-year-old, MN german shepherd presents with alopecia, erythema (red skin), crusts and pustules on his snout and paws. You suspect dermatophytosis, so you perform a Wood’s Lamp diagnostic. What should you expect to see to support your differential? What precautions should you take?
The UV light should reveal a distribution that matches the lesion you see without it. However, the Wood’s Lamp is not very sensitive (only 40-50% of M. canis will fluoresce) or specific.
You are performing a sticky tape preparation to differentiate between dermatophytes. What morphology should you expect to see for each?
- Microsporum canis
- Microsporum gypseum
- Microsporum nanum
- Trichophyton mentagrophytes
- Trichophyton verrucosum
1-4 = Macroconidia
1. Microsporum canis: tapered ends
2. Microsporum gypseum: blunt, round ends
3. Microsporum nanum: two little cells within it
4. Trichophyton mentagrophytes:
elongated and pipe-like
5 = Chlamydoconidia
5. Trichophyton verrucosum: conidia, lined up in rows
What technique to detect dermatophytosis in asymptomatic carriers?
- Mackenzie brush technique -> use of a sterile toothbursh, virgorously combing whole body for 2-3 mins -> incubate @ 25-28 ºC for 3-4 weeks
Collect fluorescent hairs, broken hairs, scales, crusts from lesion site
What sort of sample do you collect for a dermatophyte culture, and how do you transport it?
Dermatophytes eat keratin: collect nails/skin/hair and transport in a sterile container @ RT
Fungal cultures are the most sensitive method of diagnosisng dermatophytosis. How does a Dermatophyte Test Medium (DTM) identify fungal infection?
The yellow agar contains a pH indicator that turns red when present dermatophytes eat the protein in the agar and grow (low -> high pH)
What conditions are a skin biopsy required for to determine a definitive dx?
Nodular, ulcerative and vesicular lesions; nusual or severe skin lesions
Other cases:
- when hx and clinical examination suggest a dermatosis which requires histopathological dx
- when a reason dx approach has not produced a dx
- when all other rational tx fails
