31 – Diagnostic Techniques in Dermatology

Question 1

What are the DDx for folliculitis?

Answer 1

• Pyoderma
• Dermatophytosis
• Demodex canis
• (pemphigus foliaceus can present in similar fashion)

Question 2

What are some different samples you can take for cytological analysis?

Answer 2

• Impression smears
• Tape impression smears
• Scrapings
• Swab smears
• FNA

Question 3

Impression smears

Answer 3

• Good when lesions are moist or greasy
  o Beneath crusts
  o Lanced: papules, pustules, vesicles
• *better clarity than with tape

Question 4

Tape preparation

Answer 4

• Dry lesions: neck, interdigital spaces, dorsum, etc.
• Use Diff Quik to stain
  o *Do NOT use FIXATIVE
  o *Only stain with pink and purple
• Need to use CLEAR tape
• Ex. yeast=’snowman’

Question 5

Scrapings

Answer 5

• Beneath crusts, vesicles/pustules, scale
• Gently wipe onto slide
• *difference b/w scrapings for cytology and parasites (technique and methods)

Question 6

Scraping for cytology

Answer 6

• Take DRY blade and scrap lesion and smear on slide
• Stain slide in Diff Quik (fixative, pink then purple)
• *can NOT see parasites with this method
• *it is for bacteria, yeast and other cells

Question 7

Scraping for parasites

Answer 7

• # 10 blade and MINEARL oilo Put mineral oil on slide, dip blade in it before you scrap
  o Scrape
  o Wipe onto slide with mineral oil present
  o Place cover slip
  o Scan on 4x or 10x edge to edge
  o *close iris diaphragm on condenser (due to the oil)
• *deep and superficial

Question 8

Deep skin scraping

Answer 8

• Ex. for demodex sp. (mites in hair follicles)
• SQUEEZE skin first and scrape until capillary bleeding (speckling of red)
  o “confined to the one area of skin”

Question 9

Superficial skin scraping

Answer 9

• Other ectoparasites (sarcoptes, Cheyletiella)
• Scrape BROAD AREAS under crusts
• Do NOT need to cause bleeding

Question 10

Swab smears

Answer 10

• Draining tracts or sinuses
• Ear canals
• Claw folds
  o Break end
  o Tapered end can be used to scrape out exudate
• *gently role out onto slide
• Stain like normal with Diff Quik

Question 11

What are the 6 rules for when you do culture?

Answer 11

• Intracellular rods
• Previous history of Methicillin resistance infection
• Infection NOT responding to treatment
• Deep pyoderma
• Immunosuppresion
• Recurrent infection despite appropriate therapy
• **first do cytology and then culture

Question 12

How do I culture?

Answer 12

• Lance a pustule and swab
• Elevate a curst and swab
• Swab an epidermal collarette
• Tissue biopsy
• Aspirate
• Do NOT culture a draining tract DIRECTLY
  o Surface contamination

Question 13

**Tissue culture: nodular lesions

Answer 13

• Deep pyoderma: ex. acral lick dermatitis
• Deep fungal lesions: ex. kerions
• Panniculitis

Question 14

**How do you get a tissue culture?

Answer 14

1. Scrub area first (ONLY when doing this for culture, not when doing it for histopathology)
   a. We don’t care what is on surface of skin, we want to know what is DEEP
2. Rinse with sterile saline
   a. Need to make sure ALL of chlorohexidine is gone (otherwise get negative growth)
3. Take a punch biopsy (but more sterile technique, clean and new instruments and wear gloves) (don’t need to drape them)
4. Do NOT put it in formalin (put in STERILE SALINE)

Question 15

Dermatophytes: Wood’s lamp screening test

Answer 15

• Microsporum canis
• Warm up for 5-10 mins
• Infected hairs should fluoresce
  o Scale, crust, certain bacteria, certain medications, may give FALSE POSITIVES

Question 16

Dermatophytes: trichograms screening test

Answer 16

• Pluck hairs and suspend in mineral oil
• Hairs appear swollen and frayed, irregular, fuzzy
• ‘rotten log”
• No clear demarcation b/w cuticle, cortex and medulla
• Arthroconidia surround the hair
• Hyphae grow WITHIN the hair shaft
• *can also be an effective tool for finding follicular demodex mites (but skin scraping is GOLD standard)

Question 17

What else do you examine on trichograms?

Answer 17

• Distal ends for evidence of pruritus (fractured ends, etc.)
• Hair shafts for developmental defects
• Roots to determine growth phase (telogen vs. anagen)

Question 18

What are some diagnostic test for dermatophytes?

Answer 18

• PCR
• Fungal culture: dermatophyte testing medium (DTM)

Question 19

How do you do fungal culture?

Answer 19

• Pluck hairs
  o Can use wood’s lamp
  o Pluck hairs from around lesions
• MacKenzie technique (Toothbrush technique)
  o Sterile toothbrush: collect hairs and keratin

Question 20

Dermatophytes and culture medium colour

Answer 20

• FIRST use proteins
  o Alkaline metabolism turn medium from yellow to RED
• Other fungi use CHO first: will eventually turn medium to red
• *red colour change does NOT=POSITIVE
• Identify colony morphology

Question 21

Biopsy for histopathology

Answer 21

• Excellent tool
• NOT excellent for allergic dermatitis or endocrinopathy
• *Do basic diagnostics first
• Depend on PATTERNS
  o Multiple patterns can be present and can get confusing

Question 22

Biopsy: history to give pathologist

Answer 22

• Describe lesions fully
  o Pictures!
• Location
• Describe clinical history
• Describe what tests have been performed
  o Cytology and skin scraping
• What therapies have been attempted
• What are your DDx
• *paint a picture for your pathologist (it will help with your diagnosis)

Question 23

What is the best method for biopsy?

Answer 23

• Multiple samples: 5-6 samples
• Biopsy things that “look different”
  o Pustules, papules, crusts
  o DO NOT throw away crusts!!!!
• Use biggest biopsy punch you can (usually 6mm)
  o Minimum you would use=4mm (ex. nasal planum)
• Do NOT scrub
• Do NOT clip hair (can trim hairs with scissors if need be, but do NOT want to remove surface lesions)
• Take ENTIRE lesions (don’t take part disease and part normal)
  o Can get false negative results
  o Exception: if erosion or ulcer then go on the EDGE