Flashcards in Skin pathology Deck (31)
Define primary skin lesion
those which develop as a direst result of the disease process
Define secondary skin lesion
those which evolve from primary lesions OR develop as a consequence of the patient's activities.
List examples of primary skin lesions
- follicular cast
List examples of secondary skin lesions - 9
- epidermal collarette
How might the skin lesions evolve in canine superficial pyoderma?
the dominant lesions may be papules (preceding the formation of a pustule) and foal crusts (the pustule has ruptured and the exudate has dried on the skin surface)
How can you describe the configuration of skin lesions?
Give 2 examples of when you might see a single lesion
may be observed in dermatophytosis or in cutaneous neoplasia
Give 4 examples of when you might see a linear lesion
- external trauma
- lesions associated with a BV, dermatome or congenital malformation
Give examples of when you might see an annular lesion
peripheral spreading of disease as in pyoderma or dermatophytosis
When might you see a symmetrical skin lesion
a systemically-mediated disease
T/F: the distribution of disease may have important diagnostic implications
True - certain diseases most often affect particular regions of the body.
What is a 'pattern analysis'?
a method of histopathological interpretation of skin biopsies. The pattern reflects how the inflammatory cells are distributed in the skin and the types of inflammatory cells involved.
Which lesions should you select for biopsies?
- Spontaneous early lesions (macules, papules, nodules, pustules, vesicles, bullae)
- Avoid damaged lesions (excoriated, scarred or post-inflammatory pigmentation)
What should you do before taking a skin biopsy?
remove infection/infestation with bacteria, Malassezia and ectoparasites.
Outline method for taking a skin biopsy
- 6 or 8mm disposable biopsy punches. 4mm for nasal planum or footpads. Close defect with 1 or 2 sutures.
- Excisional biopsies - preferred to punch specimens for large lesions or biopsies
- LA (2% lignocaine) + sedation (more fractious animals) + GA (for excisional biopsies and for biopsy from face or distal limbs)
Why shouldn't you include a margin of unaffected skin with biopsy punches?
the specimen is too small and the lesion may be lost in processing
What sort of biopsy do you take with ulcerative skin diseases?
elliptical excisions across lesions margins to include peripheral epidermis.
Give examples of when you would take biopsies
- suspect neoplasia
- persistent ulceration
- suspicion of potentially serious diseases or those likely to require potentially hazardous treatment
- unusual presentation or lack of response to an apparently sensible therapy
- when biopsy is likely to be the only way to confirm a diagnosis (Sebaceous adenitis and follicular dystrophies)
What are the 5 main patterns of inflammation in the skin?
- Perivascular (think ectoparasite, allergy and some infections)
* N.b. different patterns are seen at different disease stages*
Describe perivascular inflammation
- Inflammatory cells around dermal BVs.
- Subclassified - superficial, mid or deep (relates to vascular plexus involved)
- Very Common
- Neutrophils - self-trauma, pyoderma
- Eosinophils - ectoparasites, hypersensitivity
- Mononuclear cells - chronic dermatitis, immunologic causes
Describe interstitial inflammation
= diffuse dermatitis = interstitial dermatitis
- means spreading out of inflammatory cells from the original perivascular pattern.
Describe interface inflammation
the dermo-epithelial junction is obscured by an accumulation of inflammatory cells (usually lymphocytes) and or by hydropic degeneration of basal keratinocyltes.
- Uncommon, but often reflects an autoimmune disease targeting the epidermis or a drug reaction
- may be pigment loss (melanocytes located near basal cells) or vesicles/bullae, and erosions/ulcers if epidermal cohesion is affected
Describe nodular inflammation
inflammatory cells found in dense clusters, especially granulomatous (or pyogranulomatous) dermatitis.
e.g. cell-mediated response e.g. FB response. acid-fast bacterial infection or deep fungal infection
Describe the 2 main types of intraepidermal pustular dermatitis
NEUTROPHILIC - pyoderma, (sterile diseases such as pemphigus)
EOSINOPHILIC - ectoparasitic infestation and hypersensitivity
When might vesicles and bullae (blisters) occur?
Intra-epidermal vesicles occur in viral infections. May result from the death of clusters of epidermal cells OR from loss of adhesion between cells. There is accumulation of fluid exudate in the defect. In contrast, in pustules (e.g. bacterial infection), inflammatory cells predominate rather than fluid.
the destruction of desmosomal attachments between keratinocytes. Either enzymatic (proteases in pyoderma) or autoimmune attack (pemphigus group).
When is presence/absence of acantholysis important?
in the assessment of the intra-epidermal vesicular or pustular dermatitis pattern of infection
Describe sub-epidermal vesicular dermatitis
the epidermis is separating from the underlying dermis. E.g. newborn animals with defects in structural proteins where normal forces --> blisters and ulcers (mechanobullous diseases) OR an acquired disease reflecting auto-immune attack on the structural proteins at this location.
inflammation of hair follicle. various parts of follicle may be involved. often preceded/accompanied by perifolliculitis (inflammation in adjacent dermis) although perifolliculitis may occur as part of a perivascular pattern since vascular plexuses invest the follicle