Dermatological diagnostics Flashcards
What ectoparasites can be identified on hair plucks?
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
What ectoparasites can be identified on superficial skin scrapes?
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
What ectoparasites can be identified on deep skin scrapes?
Follicular mites: Demodex canis, D. cati and D. injai live deep in hair follicles
What is the purpose of skin surface cytology?
to visualise cells and microbes on skin surface/in ears
Fill in the table for the different tests used for different lesions
What is the purpose of fine needle aspirates (FNA) cytology (FCP)
to visualise skin cells below surface
Describe the appearance of granulocytes when stained under a microscope
Describe the appearance of mononuclear WBCs under a microscope
What tests are routinely carried out on skin biopsies?
Histopathology
Staines
Immunohistochemistry
Tissue culture
Describe the use of analgesia for skin biopsies
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
What lesions should be sampled when taking skin biopsies?
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
What are the best sites for skin biopsies on an alopecia lesion?
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
What are the best sites for skin biopsies of an ulcerated skin lesion?
Skin just adjacent to the ulcer, where the epidermis is still intact
Where are the best sites for skin biopsies for pustules, vesicles or bullae?
Remove whole lesion without disruption
What steps should be taken to avoid skin surface disturbance when taking a skin biopsy?
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)
Describe the steps that should be taken if using local anaesthetic to assist in taking a skin biopsy
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.
What are the 2 types of skin biopsy?
Punch
Wedge
Describe the use of a punch to take a skin biopsy
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!
Describe the wedge method of taking a skin biopsy
tissue excised with scalpel
Excisional and incisional
In what situations is an excisional wedge skin biopsy preferred?
Excision of solitary nodules => histopathology
Vesicles – minimal disruption
In what situations is an incisional wedge skin biopsy preferred?
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)
Describe the preparation of a skin biopsy for histopathology
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
What are bacterial and fungal tissue cultures used to diagnose?
deep and superficial pyoderma (less affected by environmental contamination than surface sample)
Subcutaneous and deep fungal infections
Describe the preparation for bacterial and fungal tissue culture
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
What must you avoid when performing a bacterial or fungal tissue culture?
Avoid contamination with formalin/formalin fumes => kills organisms
What special considerations are there for biopsies of cutaneous masses?
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
What can cause a skin biopsy to not help diagnosis?
Incorrect sampling technique
Lesion not included in sample
Inflammatory reaction affect by therapies
Biopsy too late
What are the main histopathological patterns seen in skin disease?
Perivascular dermatitis
Interface dermatitis
Vasculitis
Nodular and/or diffuse dermatitis
Vesicular/pustular dermatitis:
- Intraepidermal
- Subepidermal
Folliculitis/furunculosis/adenitis
Panniculitis
Atrophic dermatosis
What is perivascular dermatitis?
inflammatory cells around blood vessels
Cellular infiltrate varies e.g.
Neutrophil
Lymphocytes
Eosinophil (Type 1 hypersensitivity)
What is interface dermatitis?
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
What is vasculitis?
inflammation in and around blood vessels
Tight perivascular cuffs of inflammatory cells with degeneration of vascular wall
What is nodular/diffuse dermatitis?
large lumps of inflammatory cells (nodular) or spread out (diffuse)
What is vesicular/pustular dermatitis?
blisters or pustules on skin
What is folliculitis/furunculosis/adenitis?
inflammation of the hair follicles or glands
What is panniculitis?
inflammation of subcut adipose tissue
What is atrophic dermatitis and its effect?
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
What are the signs of perivascular dermatitis?
Prominent blood vessels
WBCs around vessels
Oedema of dermis
What are the classifications of perivascular dermatitis?
Classified according to depth:
- Superficial dermal
- Mid-dermal/perifollicular
- Deep dermal
What conditions cause perivascular dermatitis?
canine atopy, pyoderma, flea atopic dermatitis
What is the effect of vasculitis?
causes microhaemorrhages
+/-:
- Panniculitis (inflammation of s/c adipose tissue)
- Dermal necrosis
- Atrophy of hair follicles => alopecia
What is the cause of vasculitis?
Either primary or secondary to inflammation, infection, drug reactions, neoplasia, vaccination
What cells are involved in nodular/diffuse dermatitis?
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
What is the cause of intraepidermal vesicular/pustular dermatitis?
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
How are intraepidermal vesicles/pustules classified?
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
Identify the lesions and disease
Subcorneal pustules – Pemphigus foliaceus
What are the causes of subepidermal vesicular/pustular dermatitis?
Autoimmune (occasionally congenital) e.g, Bullous pemphigoid, epidermolysis bullosa
Thermal burns
Severe dermal oedema
Severe interface dermatitis
What are the causes of folliculitis/furunculosis/adenitis?
bacterial infection, dermatophytosis, demodicosis, insect bites, immune-mediated diseases
what are the different types of folliculitis/furunculosis/adenitis
perifolliculitis
mural folliculitis
luminal folliculitis
bulbitis
sebaceous adenitis
What is perifolliculitis?
inflammation of perifollicular vascular plexus
What is mural folliculitis?
inflammation of follicular wall e.g., pemphigus foliaceus, demodicosis
What is luminal folliculitis?
inflammation of the lumen of the hair follicle e.g., demodicosis, dermatophytosis
What is bulbitis?
inflammation of the hair bulb e.g.,alopecia areata
What is sebaceous adenitis?
Inflammation of the sebaceous glands e.g., autoimmune and leishmaniasis
What is furunculosis?
rupture of hair follicle with release of keratin into dermis => marked inflammatory response
What are the causes of panniculitis?
Sometimes an extension of follicular disease
infectious agents
vasculitis
foreign body
pancreatic disease
trauma
sterile idiopathic
What are the causes of atrophic dermatosis?
Various endocrine causes – hormone assays needed to distinguish (eg HAC, hypothyroidism)
Any chronic systemic disease or malnutrition
