Skin pathology

Question 1

Define primary skin lesion

Answer 1

those which develop as a direst result of the disease process

Question 2

Define secondary skin lesion

Answer 2

those which evolve from primary lesions OR develop as a consequence of the patient’s activities.

Question 3

List examples of primary skin lesions

Answer 3

• macule
• patch
• wheal
• papule
• nodule
• tumour
• vesicle
• bulla
• pustule
• comedo
• follicular cast
• alopecia
• scale
• crust

Question 4

List examples of secondary skin lesions - 9

Answer 4

• epidermal collarette
• scar
• excoriation
• erosion
• ulcer
• fissure
• lichenification
• hyperpigmentation
• callus

Question 5

How might the skin lesions evolve in canine superficial pyoderma?

Answer 5

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)

Question 6

How can you describe the configuration of skin lesions?

Answer 6

Single,
linear
annular
symmetrical

Question 7

Give 2 examples of when you might see a single lesion

Answer 7

may be observed in dermatophytosis or in cutaneous neoplasia

Question 8

Give 4 examples of when you might see a linear lesion

Answer 8

• external trauma

- lesions associated with a BV, dermatome or congenital malformation

Question 9

Give examples of when you might see an annular lesion

Answer 9

peripheral spreading of disease as in pyoderma or dermatophytosis

Question 10

When might you see a symmetrical skin lesion

Answer 10

a systemically-mediated disease

Question 11

T/F: the distribution of disease may have important diagnostic implications

Answer 11

True - certain diseases most often affect particular regions of the body.

Question 12

What is a ‘pattern analysis’?

Answer 12

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.

Question 13

Which lesions should you select for biopsies?

Answer 13

• Spontaneous early lesions (macules, papules, nodules, pustules, vesicles, bullae)
• Avoid damaged lesions (excoriated, scarred or post-inflammatory pigmentation)

Question 14

What should you do before taking a skin biopsy?

Answer 14

remove infection/infestation with bacteria, Malassezia and ectoparasites.

Question 15

Outline method for taking a skin biopsy

Answer 15

• 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)

Question 16

Why shouldn’t you include a margin of unaffected skin with biopsy punches?

Answer 16

the specimen is too small and the lesion may be lost in processing

Question 17

What sort of biopsy do you take with ulcerative skin diseases?

Answer 17

elliptical excisions across lesions margins to include peripheral epidermis.

Question 18

Give examples of when you would take biopsies

Answer 18

• 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)

Question 19

What are the 5 main patterns of inflammation in the skin?

Answer 19

• Perivascular (think ectoparasite, allergy and some infections)
• Diffuse/interstitial
• Nodular
• Panniculitis
• Interface
• N.b. different patterns are seen at different disease stages*

Question 20

Describe perivascular inflammation

Answer 20

• 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

Question 21

Describe interstitial inflammation

Answer 21

= diffuse dermatitis = interstitial dermatitis

- means spreading out of inflammatory cells from the original perivascular pattern.

Question 22

Describe interface inflammation

Answer 22

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

Question 23

Describe nodular inflammation

Answer 23

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

Question 24

Describe the 2 main types of intraepidermal pustular dermatitis

Answer 24

NEUTROPHILIC - pyoderma, (sterile diseases such as pemphigus)
EOSINOPHILIC - ectoparasitic infestation and hypersensitivity

Question 25

When might vesicles and bullae (blisters) occur?

Answer 25

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.

Question 26

Define acantholysis

Answer 26

the destruction of desmosomal attachments between keratinocytes. Either enzymatic (proteases in pyoderma) or autoimmune attack (pemphigus group).

Question 27

When is presence/absence of acantholysis important?

Answer 27

in the assessment of the intra-epidermal vesicular or pustular dermatitis pattern of infection

Question 28

Describe sub-epidermal vesicular dermatitis

Answer 28

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.

Question 29

Define folliculitis

Answer 29

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

Question 30

Define furunculosis

Answer 30

inflammatory destruction of hair follicle with rupture and extrusion of follicle contents into the dermis –> FB response in dermis (often suppurative and/or chronic pyogranulomatous inflammation) which may –> scars, fistula formation or panniculitis. Most commonly seen in biopsies of dogs with deep pyoderma.

Question 31

What is an atrophic pattern?

Answer 31

not an inflammatory skin pattern but is characterised by reductions in the size of different components of the skin, most commonly epidermal thinning with small telogen-phase follicles as a consequence of an endocrine disease.