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LEAH FCP > Dermatological diagnostics > Flashcards

Dermatological diagnostics Flashcards

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1
Q

What are the key steps in dermatological diagnostics?

A

Choose tests wisely – prioritise those that provide quick, non-invasive & cost-effective information

Take high-quality samples – ensure adequate quantity & correct technique

Examine & interpret samples correctly – use proper microscopy techniques

Consider limitations – be aware of false negatives & test sensitivity

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2
Q

What are the most commonly used dermatological diagnostic tests and what are they used for?

A

Coat brushing – Surface parasites/fleas

Acetate tape strip unstained - Surface parasites, objective x4-10

Skin scrapings – superficial & deep parasites, objective x4-10

Trichogram – Demodex, nits, dermatophytosis, hair cycle abnormalities, objective x4-40

Cytology – Bacteria, yeasts, cells, objective x4-100

Wood’s lamp - Micosporum canis

McKenzie coat brush - Dermatophytes

Culture - bacteria, yeasts

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3
Q

What are these parasites?

A

1= Cheyletiella
2 = Sarcoptes
3 = Demodex

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4
Q

What can be identified in hair plucks?

A

Lice & Cheyletiella eggs are found attached to hair shafts

In follicular diseases (demodex, Dermatophytosis & sebaceous adenitis) may see follicular casts

Demodex canis, D. cati & D. injai may be seen on hair plucks

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5
Q

What can be identified in superficial skin scrapes?

A

Non-burrowing mites: Demodex gatoi (cats), Cheyletiella spp. (dogs, cats & rabbits)

Burrowing mites: Sarcoptes scabiei (dogs) & Trixicarus caviae (guinea pigs)

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6
Q

What can be identified in deep skin scrapes?

A

Follicular mites: Demodex canis, D. cati & D. injai

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7
Q

What kind of lesions are sampled and what staining is used for direct impression smears (cytology)?

A

Moist/greasy lesions
Ruptured pustules
Skin under crusts
Accessible sites

All 3 Diff-quick solutions: A fixative + B eosin + C methylene blue

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8
Q

What kind of lesions are sampled and what staining is used for indirect impression smears (cytology)?

A

Ear canals

All 3 Diff-quick solutions: A fixative + B eosin + C methylene blue

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9
Q

What kind of lesions are sampled and what staining is used for acetate tape strip (cytology)?

A

Dry lesions
Less accessible sites

B eosin + C methylene blue

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10
Q

What microbe can you see in this cytology example?

A

Rods (x620)

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11
Q

What microbe can you see in this cytology example?

A

Neutrophils with intracellular cocci (x1000)

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12
Q

What microbe can you see in this cytology example?

A

Malassezia, corneocytes (x1000)

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13
Q

Label these WBCs (simplified)

A
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14
Q

Label these WBCs (simplified)

A
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15
Q

Why perform a skin biopsy?

A

To obtain definitive diagnosis when other methods are inconclusive

To identify deep infections, autoimmune diseases, neoplasia, vasculitis

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16
Q

Which tests are carried out on skin biopsies?

A

Histopathology
Tissue culture

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17
Q

How are skin biopsies stained?

A

Usually haematoxylin & eosin (H&E)

Special stains:
- Periodic Acid Schiff (PAS) for fungi
- Giemsa for bacteria
- Ziehl-Neelsen (ZN) for mycobacteria
- Immunohistochemistry

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18
Q

Is sedation or GA required for skin biopsies?

A

In calm animals, biopsies usually taken using sedation & local anaesthesia

General anaesthesia usually required for biopsies of feet, pinnae, lips & noses

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19
Q

What needs to be sampled in skin biopsies?

A

Sample representative range of lesions

Take multiple samples (min. 3, unless solitary lesion)

Sample fully developed primary lesions where possible, avoiding traumatised skin/necrotic crust

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20
Q

Where would you sample this site (for alopecia)?

A
  1. Across margin of alopecic area
  2. Area of maximum hair loss
  3. Normal haired skin wedge

Wedge biopsy

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21
Q

Where would you sample this site (for ulcerated skin)?

A

Skin just adjacent to ulcer, where epidermis is still intact

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22
Q

Where would you sample this site (for pustules, vesicles or bullae)?

A

Remove whole lesion without disruption (Often very delicate)

Difficult with punch not to cause damage so wedge biopsy best

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23
Q

How do you prepare a sample site for skin biopsy?

A

Avoid disturbing skin surface!
- Even gentle cleaning can remove many layers of stratum corneum

Clip hair, but not too short – scissors often preferable to clippers

Don’t disturb crusts or skin surface – include crusts!

Don’t prep or scrub skin (unless excisional biopsy of nodules)

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24
Q

How do you mark and anaesthetise the site for a skin biopsy?

A

If infiltrating local anaesthetic:
- Draw circle around lesion in indelible marker
- Infiltrate LA into subcutis around periphery of circle
- Care not to exceed max volume of LA for patient’s weight
- Check efficacy of analgesia by pricking with a needle

Can draw orientation line along line of hair growth for cases of alopecia as better chance of longitudinal hair sections

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25
Describe punch biopsies
Quick and convenient Ideal for superficial lesions Use 6mm or 8mm biopsy punches routinely, 3mm/4mm only for delicate structures Hold perpendicular to skin surface Rotate in one direction, not back & forth Don't reuse blunt biopsy punches
26
Describe wedge biopsies
Tissue excised with scalpel Excisional for: - Excision of solitary nodules --> histopathology - Vesicles – minimal disruption Incisional for: - Transition from normal to lesional skin - Biopsy of cutaneous masses - If pathology suspected in deep dermis/subcutis, e.g. panniculitis (inflammation of s/c fat)
27
What are the key steps in preparing a skin biopsy for histopathology?
1. Blot blood gently from underside of sample 2. Place promptly into 10% formalin – use min. 10x volume of tissue sample 3. For thin samples, prevent curling by placing them on stiff card, then immerse in formalin 4. Separate 'normal', marginal & central lesions in different pots Help pathologist by providing brief history & differential diagnoses
28
When should bacterial and fungal tissue culture be performed?
Deep & superficial pyoderma (Less affected by environmental contamination than surface sample) Subcutaneous & deep fungal infections
29
How should tissue be prepared for culture?
1. Withdraw antibiotics (5–7 days) & topical antimicrobials (≥3 days) before sampling 2. Gently blot surface with alcohol swab to remove contamination & let dry 3. Punch biopsy & place it in sterile glass tube +- sterile saline Avoid formalin exposure, as it kills organisms Store appropriately – many organisms survive in fridge or freezer & can be stored post-histopathology
30
How should cutaneous masses be biopsied?
Incisional biopsy (wedge) → preferred for invasive neoplasms to guide treatment Excisional biopsy → for removal of entire mass with margins for histopathology Max. 1cm tissue thickness for adequate fixation
31
Why is an incisional biopsy preferred before excising a suspected neoplasm (cutaneous masses)?
Helps determine tumour type before removal Ensures adequate margins during final excision Biopsy tracts should be removed with the tumour to prevent spread
32
What are common reasons why skin biopsy results may not be conclusive?
Poor technique Sample examined not representative of lesion - Ask pathologist to cut further sections if suspect this - Put visible lesions centrally in biopsy Lesion altered by treatment Biopsy taken too late – early lesions are better for vasculitis Unrealistic expectations – some diseases can't be distinguished on biopsy
33
What is pattern analysis in dermatology?
Method of categorising skin lesions based on histological patterns Helps narrow down differential diagnoses & guide further testing
34
What are the main histopathological patterns seen in skin disease?
1. Perivascular Dermatitis – Inflammatory cells around blood vessels 2. Interface Dermatitis – Cells abutting basement membrane 3. Vasculitis – Inflammation in & around blood vessels 4. Nodular/Diffuse Dermatitis – Large lumps of inflammatory cells (nodular) or spread out (diffuse) 5. Vesicular/Pustular Dermatitis – Blisters or pustules on skin a) Intraepidermal b) Subepidermal 6. Folliculitis/Furunculosis/Adenitis – Inflammation of hair follicles or glands 7. Panniculitis – Affects subcutaneous fat 8. Atrophic Dermatosis – Thin, weakened skin due to hormones or blood supply issues
35
What is perivascular dermatitis, and what conditions cause it?
Inflammatory cells (neutrophils, lymphocytes, eosinophils (Type 1 hypersensitivity)) exit blood vessels & move into tissue Clinical signs: - Prominent blood vessels - WBCs around vessels - Oedema of dermis Classified according to depth - Superficial dermal - Mid-dermal/perifollicular - Deep dermal Seen in allergic diseases (atopy, flea allergy dermatitis), bacterial pyoderma
36
What is interface dermatitis, and what conditions cause it?
Band-like infiltrate of immune cells at the dermo-epidermal junction Basal keratinocyte degeneration, pigment incontinence, apoptosis Can cause erosions & ulcerations through clefting Seen in immune-mediated diseases
37
What is vasculitis, and what conditions cause it?
Inflammation of blood vessels - Inflammatory cells tightly surround blood vessels, causing vascular wall degeneration Leads to microhemorrhages, dermal necrosis, panniculitis, alopecia Either primary or secondary to inflammation, infection, drug reactions, neoplasia, vaccination so look for primary cause Can be difficult to find as lesions short-lived, need to biopsy early lesion & take multiple samples
38
What is going on here?
(Post-vaccination) vasculitis with well-demarcated areas of necrosis and alopecia
39
What cells are seen in nodular/diffuse dermatitis?
Convergence of nodules --> diffuse pattern Very common in dogs Cells vary: - Neutrophils - pyogenic agents - Macrophages (granulomatous inflammation)– e.g. foreign bodies, mycobacteria - Neutrophils & macrophages (pyogranulomatous inflammation) – e.g. fungi - Eosinophilic – parasitic? - Lymphocytic – insect bites, vaccine reactions
40
What histological pattern can be seen here?
Nodular granulomatous dermatitis of cat – due to deep Microsporum canis infection
41
What causes vesicles or pustules in intraepidermal dermatitis?
Epidermal inflammation (spongiosis) – Intercellular oedema (parasites, infection) Acantholysis – Loss of cell adhesion due to infection or autoimmune disease Intracellular oedema – Due to mechanical forces
42
How are intraepidermal vesicles/pustules classified?
Subcorneal (superficial) – Pemphigus foliaceus, pyoderma Suprabasal (deeper) – Pemphigus vulgaris Follicular external root sheath – Pemphigus foliaceus
43
What cellular infiltrate is often seen in intraepidermal dermatitis?
Neutrophils - Bacterial pyoderma, PF Eosinophils - PF, parasite
44
What is the difference between pemphigus foliaceus and pemphigus vulgaris?
Pemphigus foliaceus (PF) – Superficial pustules under stratum corneum, fragile, ruptures easily Pemphigus vulgaris – Deeper pustules, more tense & less likely to burst
45
What histological features are seen in pemphigus foliaceus?
Pustules under stratum corneum filled with neutrophils & acantholytic cells Thickened epidermis due to chronic inflammation Diffuse dermal inflammation beneath pustules
46
What causes the acantholytic cells in pemphigus foliaceus?
Type II hypersensitivity targeting desmosomes, leading to loss of cell adhesion (acantholysis) Results in floating keratinocytes (acantholytic cells) in pustules
47
What is subepidermal vesicular/pustular dermatitis?
Separation of epidermis from dermis Causes severe clinical effects & is difficult to biopsy accurately
48
What are the causes of subepidermal vesicular dermatitis?
Autoimmune diseases: Bullous pemphigoid, epidermolysis bullosa Thermal burns Severe dermal oedema & interface dermatitis. Occasionally artefact in biopsy processing
49
What are the different types of folliculitis/furunculosis/ adenitis?
Perifolliculitis – inflammation around hair follicle plexus (early stage) Mural folliculitis – inflammation within follicle wall (Pemphigus foliaceus, demodicosis) Luminal folliculitis – infection inside follicle (Demodex, dermatophytosis) Bulbitis – affects hair bulb (Alopecia areata – rare) Sebaceous adenitis - affects sebaceous glands (auto-immune & Leishmaniasis) Furunculosis - rupture of hair follicle with release of keratin into dermis --> marked inflammatory response (deep pyoderma, Demodex)
50
Label the histological patterns
51
Label the histological patterns
52
What is panniculitis, and what causes it?
Inflammation of subcutaneous fat Sometimes extension of follicular disease Causes: Infectious agents, vasculitis, trauma, foreign bodies, pancreatic disease May be sterile idiopathic, but infection must be ruled out first
53
What causes atrophic dermatosis, and how does it appear histologically?
Caused by endocrine diseases (Cushing’s, hypothyroidism) or chronic illness/malnutrition Histology: - Epidermal, follicular, sebaceous gland atrophy - Orthokeratotic hyperkeratosis. - Follicular keratosis +/- calcinosis cutis (Cushing’s disease)
54
Define acanthocyte & acantholysis
Acanthocyte: epidermal cell free in vesicle/pustule, caused by acantholysis Acantholysis: loss of cohesion between cells of living epidermis
55
Define Dyskeratosis
Abnormal, premature or imperfect keratinisation of keratinocytes
56
Define Exocytosis
Migration of inflammatory cells from dermis to epidermis
57
Define Hyperkeratosis
Increase in stratum corneum
58
Define orthokeratosis and parakeratosis
Orthokeratosis: excessive cornification – keratinocytes lose nuclei Parakeratosis: excessive cornification – keratinocytes retain nuclei
59
Label the histological pattern
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Label the histological pattern
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63
Label the histological pattern

LEAH FCP (151 decks)

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