Diagnostic Approaches to Skin Disease Flashcards

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1
Q

Considerations for diagnostic testing

A

Prioritise which tests will help you narrow down differentials
Take an adequate number of good quality samples
Examine efficiently
Be aware of limitations
* False positives
* False negatives

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2
Q

Diagnostic tests for ectoparasites

A

Coat brushing
Unstained acetate tape
Skin scrapings (deep and superficial)
Trichograms

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3
Q

Diagnostic tests for bacteria

A

Cytology
Microbial swab for culture

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4
Q

Diagnostic tests for fungi

A

Trichograms (dermatophytes on shaft)
Cytology (yeasts)
Wood’s lamp (Microsporum canis)
McKenzie coat brush (dermatophytes for culture)
Microbial swab for culture (yeasts)

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5
Q

Skin surface cytology tests

A

Used to visualise cells and microbes on skin surface
* Direct impression smear
* Cotton bud impression smear
* Acetate tape strip

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6
Q

Type of lesion for direct impression smear

A

Most/greasy lesions
Ruptured pustule
Skin under crusts
Accessible sites

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7
Q

Type of lesion for cotton bud smear

A

Ear canals

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8
Q

Type of lesion for stained acetate tape strip

A

Dry lesion
Less accessible locations

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9
Q

Staining for direct impression smear

A

All 3 diff quick solutions
A - Fixative
B - Eosin
C - Methylene blue

Dip method

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10
Q

Staining for cotton bud smear

A

All 3 Diff-quick solutions
A - Fixative
B - Eosin
C - Methylene blue

Rack method

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11
Q

Staining for acetate tape strip

A

Only B and C
*Dip method

Or C only
* Pipette

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12
Q

Fine needle aspirate cytology

A

To visualise skin cells below surface

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13
Q

Eosinophil granule colour using H&E stain

A

Pink - Eosinophilic

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14
Q

Neutrophil granule colour using H&E stain

A

Granules don’t stain

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15
Q

Basophil granule colour using H&E stain

A

Dark blue - Basophilic

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16
Q

Why do we biopsy the skin?

A
  • To establish a definitive diagnosis that can’t be reached by less invasive testing methods
  • To rule out other conditions
17
Q

What tests are carried out on skin biopsies?

A

Histopathology
* Allows assessment of tissue architecture
* Usually staid with H&E

Tissue Culture
* To culture and identify Bactria/fungi below skin surface

18
Q

When to use sedation/anaesthesia

A

Can generally carry out biopsies under sedation and local anaesthetic
Use GA for biopsies of feet, lips and noses

19
Q

How many samples should you take?

A

Sample a representative range of lesions
Take a minimum of 3 unless solitary lesion
Sample fully developed primary lesions
* Avoid traumatised skin and necrotic crust

20
Q

Samples for alopecia

A

○ Across margin of alopecia
○ Area of maximum hair loss
○ Normal haired skin
Wedge shape across margin is useful

21
Q

Samples for ulcerated skin

A

○ Skin adjacent to ulcer where epidermis is sill intact
Wedge shape across margin is useful

22
Q

Samples for Pustules, vesicles or bullae

A

Remove whole lesion without disruption
Wedge biopsy is best

23
Q

How to prepare sample site

A

Don’t disturb skin surface
○ Clip hair with scissors
○ Do not disturb crust
○ Do not prep or scrub
Unless excisional biopsy of sub cut nodules

24
Q

How to prepare sample site when using LA

A

○ Draw circle around lesion in indelible marker
○ Infiltrate LA into subcutis around periphery of circle
○ Do not exceed maximum volume of LA for patients weight
○ Check efficacy of analgesia by pricking with needle

25
Q

Types of biopsy

A

Punch biopsy
Wedge/ellipse
* Excisional
* Incisional

26
Q

Punch biopsies

A

○ Quick and convenient
○ Use 6-8mm biopsy punches routinely
3/4mm for delicate structures
○ Don’t destroy/shear sample
Rotate in one direction only
Hold perpendicular to skin surface
Do not reuse blunt punches

27
Q

Wedge/ellipse biopsy

A

Tissue excised with a scalpel

28
Q

Excisional biopsy

A

Used for solitary nodules
Vesicles
Cut all the way around lesion

29
Q

Incisional biopsy

A

Transition from normal to lesions skin
Biopsy of cutaneous masses
Used if pathology suspend in deep dermis/subcutis

30
Q

How to handle sample appropriately

A

Never handle dermis or epidermis
* Only handle by subcutis

For histopathology
○ Blot blood gently from underside of sample
○ Place promptly into 10% formalin
Minimum 10x volume of tissue sample
○ If thin sample
Place on stiff card or end of wooden tongue depressor to prevent curling
○ Give pathologist brief history and suspected differential diagnoses

31
Q

Considerations for cutaneous masses

A
  • May not be homogenous
    ○ Especially if large
    ○ Incisional or excisional likely to be more representative than punch
  • If suspect invasive neoplasm
    ○ Take incisional biopsy fist before attempting removal
    Helps ensure adequate margins taken when removal performed
32
Q

Considerations for bacterial and fungal culture

A
  • Used for deep and superficial pyoderma, deep fungal infections
    ○ Less affected by environmental contamination than surface sample
  • Withdraw antibiotics for 5-7 days, topical antimicrobials 3+ days prior to sampling for bacterial culture