Dermatological diagnostics

Question 1

Answer 1

Question 2

What ectoparasites can be identified on hair plucks?

Answer 2

Lice and Cheyletiella eggs are found attached to hair shafts.
In follicular diseases (demodex, Dermatophytosis & sebaceous adenitis) you may see follicular casts
Demodex canis, D. cati & D. injai may be seen on hair plucks

Question 3

What ectoparasites can be identified on superficial skin scrapes?

Answer 3

Non-burrowing mites: Demodex gatoi (cats), Cheyletiella spp. (dogs, cats and rabbits) are found on the surface of the skin

Burrowing mites: Sarcoptes scabiei (dogs) and Trixicarus caviae (guinea pigs) make tunnels in the epidermis

Question 4

What ectoparasites can be identified on deep skin scrapes?

Answer 4

Follicular mites: Demodex canis, D. cati and D. injai live deep in hair follicles

Question 5

What is the purpose of skin surface cytology?

Answer 5

to visualise cells and microbes on skin surface/in ears

Question 6

Fill in the table for the different tests used for different lesions

Answer 6

Question 7

What is the purpose of fine needle aspirates (FNA) cytology (FCP)

Answer 7

to visualise skin cells below surface

Question 8

Describe the appearance of granulocytes when stained under a microscope

Answer 8

Question 9

Describe the appearance of mononuclear WBCs under a microscope

Answer 9

Question 10

What tests are routinely carried out on skin biopsies?

Answer 10

Histopathology
Staines
Immunohistochemistry
Tissue culture

Question 11

Describe the use of analgesia for skin biopsies

Answer 11

In calm animals, biopsies can frequently be taken using sedation and local anaesthesia.
General anaesthesia usually required in all animals for biopsies of feet, pinnae, lips and noses

Question 12

What lesions should be sampled when taking skin biopsies?

Answer 12

Sample a representative range of lesions
Take multiple samples (minimum 3, unless a solitary lesion)
Sample fully developed primary lesions where possible, avoiding traumatised skin / necrotic crust

Question 13

What are the best sites for skin biopsies on an alopecia lesion?

Answer 13

Across the margin of the alopecic area
the area of maximum hair loss
normal haired skin wedge biopsy across margin of alopecic area often more useful than punch

Question 14

What are the best sites for skin biopsies of an ulcerated skin lesion?

Answer 14

Skin just adjacent to the ulcer, where the epidermis is still intact

Question 15

Where are the best sites for skin biopsies for pustules, vesicles or bullae?

Answer 15

Remove whole lesion without disruption

Question 16

What steps should be taken to avoid skin surface disturbance when taking a skin biopsy?

Answer 16

Clip hair, but not too short – scissors often preferable to clippers
Do not disturb crusts or skin surface – include crusts!
Do not prep or scrub the skin (unless excisional biopsy of nodules)

Question 17

Describe the steps that should be taken if using local anaesthetic to assist in taking a skin biopsy

Answer 17

Draw circle around lesion in indelible marker
Infiltrate local anaesthetic into the subcutis around periphery of circle
Care not to exceed maximum volume of local anaesthetic for your patient’s weight!
Check efficacy of analgesia by pricking with a needle.

Question 18

What are the 2 types of skin biopsy?

Answer 18

Punch
Wedge

Question 19

Describe the use of a punch to take a skin biopsy

Answer 19

Quick and convenient
Use 6mm or 8mm biopsy punches routinely, 3mm/4mm only for delicate structures
Hold perpendicular to skin surface
Rotate in one direction, not back and forth
Do not reuse blunt biopsy punches!

Question 20

Describe the wedge method of taking a skin biopsy

Answer 20

tissue excised with scalpel
Excisional and incisional

Question 21

In what situations is an excisional wedge skin biopsy preferred?

Answer 21

Excision of solitary nodules => histopathology
Vesicles – minimal disruption

Question 22

In what situations is an incisional wedge skin biopsy preferred?

Answer 22

Transition from normal to lesional skin
Biopsy of cutaneous masses
If pathology suspected in the deep dermis/subcutis, e.g. panniculitis (inflammation of s/c fat)

Question 23

Describe the preparation of a skin biopsy for histopathology

Answer 23

Blot blood gently from the underside of sample
If thin sample, place on piece of stiff card or end of wooden tongue depressor (subcutaneous tissue down) to prevent curling.
Place promptly into 10% formalin
Separate ‘normal’, marginal and central lesions in different pots

Question 24

What are bacterial and fungal tissue cultures used to diagnose?

Answer 24

deep and superficial pyoderma (less affected by environmental contamination than surface sample)
Subcutaneous and deep fungal infections

Question 25

Describe the preparation for bacterial and fungal tissue culture

Answer 25

Withdraw antibiotics for 5-7 days, topical antimicrobials 3+ days prior to sampling for bacterial culture Gently blot surface with alcohol swab to remove contamination and allow to dry

Question 26

What must you avoid when performing a bacterial or fungal tissue culture?

Answer 26

Avoid contamination with formalin/formalin fumes => kills organisms

Question 27

What special considerations are there for biopsies of cutaneous masses?

Answer 27

If suspect an invasive neoplasm, take incisional biopsy first to identify mass before attempting removal – helps to ensure adequate margins taken when removal performed Ensure biopsy tracts are excised, with adequate margins, when tumour subsequently removed Remove deeper tissue in one and submit untrimmed to look for spread Maximum 1cm tissue thickness for adequate fixation

Question 28

What can cause a skin biopsy to not help diagnosis?

Answer 28

Incorrect sampling technique Lesion not included in sample Inflammatory reaction affect by therapies Biopsy too late

Question 29

What are the main histopathological patterns seen in skin disease?

Answer 29

Perivascular dermatitis Interface dermatitis Vasculitis Nodular and/or diffuse dermatitis Vesicular/pustular dermatitis: - Intraepidermal - Subepidermal Folliculitis/furunculosis/adenitis Panniculitis Atrophic dermatosis

Question 30

What is perivascular dermatitis?

Answer 30

inflammatory cells around blood vessels Cellular infiltrate varies e.g. Neutrophil Lymphocytes Eosinophil (Type 1 hypersensitivity)

Question 31

What is interface dermatitis?

Answer 31

Cell-rich or cell-poor band-like mononuclear infiltrate crossing dermo-epidermal junction degeneration of basal keratinocytes Pigment incontinence +/- apoptosis can cause erosions and ulceration through clefting associated with immune-mediated disease

Question 32

What is vasculitis?

Answer 32

inflammation in and around blood vessels Tight perivascular cuffs of inflammatory cells with degeneration of vascular wall

Question 33

What is nodular/diffuse dermatitis?

Answer 33

large lumps of inflammatory cells (nodular) or spread out (diffuse)

Question 34

What is vesicular/pustular dermatitis?

Answer 34

blisters or pustules on skin

Question 35

What is folliculitis/furunculosis/adenitis?

Answer 35

inflammation of the hair follicles or glands

Question 36

What is panniculitis?

Answer 36

inflammation of subcut adipose tissue

Question 37

What is atrophic dermatitis and its effect?

Answer 37

thin, weakened skin due to hormones or blood supply issues atrophy of: - epidermis - hair follicles - sebaceous glands Orthokeratotic hyperkeratosis Follicular keratosis +/- calcinosis cutis if HAC

Question 38

What are the signs of perivascular dermatitis?

Answer 38

Prominent blood vessels WBCs around vessels Oedema of dermis

Question 39

What are the classifications of perivascular dermatitis?

Answer 39

Classified according to depth: - Superficial dermal - Mid-dermal/perifollicular - Deep dermal

Question 40

What conditions cause perivascular dermatitis?

Answer 40

canine atopy, pyoderma, flea atopic dermatitis

Question 41

What is the effect of vasculitis?

Answer 41

causes microhaemorrhages +/-: - Panniculitis (inflammation of s/c adipose tissue) - Dermal necrosis - Atrophy of hair follicles => alopecia

Question 42

What is the cause of vasculitis?

Answer 42

Either primary or secondary to inflammation, infection, drug reactions, neoplasia, vaccination

Question 43

What cells are involved in nodular/diffuse dermatitis?

Answer 43

Neutrophils - pyogenic agents Macrophages (granulomatous inflammation)– e.g. foreign bodies, mycobacteria Neutrophils and macrophages (pyogranulomatous inflammation) – e.g. fungi Eosinophilic – parasitic? Lymphocytic – insect bites, vaccine reactions

Question 44

What is the cause of intraepidermal vesicular/pustular dermatitis?

Answer 44

Epidermal inflammation/spongiosis - intercellular oedema in epidermis due to parasites or infection Acantholysis - loss of cohesion between cells of the living epidermis, desmosomes destroyed - due to infection or autoimmune disease Intracellular oedema due to mechanical forces

Question 45

How are intraepidermal vesicles/pustules classified?

Answer 45

By position: - subcorneal (v superficial) e.g., pemphigus foliaceus (PF), pyoderma - suprabasilar (deeer) e.g., pemphigus vulgaris - in follicular external root sheath e.g., PF Cellular infiltrate: - neutrophils e.g., bacterial pyoderma, PF - eosinophils e.g., PF, parasites

Question 46

Identify the lesions and disease

Answer 46

Subcorneal pustules – Pemphigus foliaceus

Question 47

What are the causes of subepidermal vesicular/pustular dermatitis?

Answer 47

Autoimmune (occasionally congenital) e.g, Bullous pemphigoid, epidermolysis bullosa Thermal burns Severe dermal oedema Severe interface dermatitis

Question 48

What are the causes of folliculitis/furunculosis/adenitis?

Answer 48

bacterial infection, dermatophytosis, demodicosis, insect bites, immune-mediated diseases

Question 49

what are the different types of folliculitis/furunculosis/adenitis

Answer 49

perifolliculitis mural folliculitis luminal folliculitis bulbitis sebaceous adenitis

Question 50

What is perifolliculitis?

Answer 50

inflammation of perifollicular vascular plexus

Question 51

What is mural folliculitis?

Answer 51

inflammation of follicular wall e.g., pemphigus foliaceus, demodicosis

Question 52

What is luminal folliculitis?

Answer 52

inflammation of the lumen of the hair follicle e.g., demodicosis, dermatophytosis

Question 53

What is bulbitis?

Answer 53

inflammation of the hair bulb e.g.,alopecia areata

Question 54

What is sebaceous adenitis?

Answer 54

Inflammation of the sebaceous glands e.g., autoimmune and leishmaniasis

Question 55

What is furunculosis?

Answer 55

rupture of hair follicle with release of keratin into dermis => marked inflammatory response

Question 56

What are the causes of panniculitis?

Answer 56

Sometimes an extension of follicular disease infectious agents vasculitis foreign body pancreatic disease trauma sterile idiopathic

Question 57

What are the causes of atrophic dermatosis?

Answer 57

Various endocrine causes – hormone assays needed to distinguish (eg HAC, hypothyroidism) Any chronic systemic disease or malnutrition