Derm 4 Flashcards
Diagnosing disease
- Determine what skin lesion is and what it means
- Start with skin scrapings and cytology
Collection methods for cytology
-impression smears
-tape impression smears
-scrapings
-swab smears
-FNA
When to do impression smears?
For moist or greasy lesions
-beneath crusts or for lanced papules, pustules, vesicles
When to do tape preparations?
Used for dry lesions (neck, interdigital spaces, dorsum)
*use diff quik to stain, but do not use fixative (pink and purple)
When to do skin scrapings?
-beneath crusts, vesicles/pustules, scale
-different scraping technique for skin vs. parasites
**Cytology: dry blade (no mineral oil), put on slide, then stain (fixative, pink, purple) –> will not see parasites with this technique!
When to do swab smears?
-draining tracts, ear canals, claw folds
-gently roll out onto slides
Skin scraping for parasites
10 blade and mineral oil
=mineral oil on slide, dip blade in oil before scraping, then wipe scraping on oil on slide, cover slip , observe at 4x -10x power
Deep: squeeze skin first, and then scrape until capillary bleeding eg. Demodex
Superficial: scrape broad areas, under crusts; do not need to cause bleeding
Microscopy of cytology vs parasite skin scraping
Cytology: high light; high condenser
Parasite skin: close iris diaphragm on condenser= lower condenser
When to culture?
*always do cytology first to confirm that you have infection before culture
How to culture?
-lance a pustule and swab
-elevate a crust and swab
-swab an epidermal collarette
-tissue biopsy
-aspirate
Can you culture a draining tract?
no because there is surface contaminants
Tissue cultures
Need tissue biopsy for culture on nodules! Because nodules mean infection is deep in skin
Biopsy uses
-tissue culture or histopathology
Performing tissue culture
- Scrub- Only scrub when taking biopsies for tissue culture
*no scrub for histopathology - Rinse with sterile saline to remove all chlorohexadine
- punch biopsy with sterile technique
- put in sterile saline … not formalin
Dermatophytes
Ringworm
Couple methods:
1. use woods lamp= warm up 5-10mins and then test to see if hair fluoresce
2. Trichograms= pluck hair, suspend in mineral oil= positive for ringworm if frayed rotten wood appearance
*can also use this to find demodex mites but skin scraping is gold standard
What can trichograms be used for?
-dermatophytes
-demodex
-evidence of pruritus
-developmental defects
-look at roots to determine growth or resting phase (telogen vs. anagen)
Fungal cultures
- Pluck hairs = woods lamp
- Toothbrush (Mackenzie) = sterile toothbrush to collect hairs and keratin
*often fungi turns red but this does not always mean positive
What are you looking for in fungal culture?
Find macroconidia
-tape and lactophenol blue stain
What can biopsy not be used to diagnose?
-allergic dermatitis
-endocrinopathy
What to give to pathologist?
-send pictures
-give them information/ descriptions = patterns
-tell them location
-tell them previous tests, clinical history, successful or unsuccessful treatments
-tell them your DDx list
-multiple samples (5-6)
-give them crusts with formalin and biopsy samples
Biopsy methods
-typically 6mm punch
*might use 4mm for areas that may be hard to close
-do not clip hair or scrub! (different than cultures!!)
-take the entire lesion = do not need to take edge biopsy for part healthy and part unhealthy.. can lead to false negatives
*exception= ulcers or erosion should biopsy edge
