Skin Pathology

Question 1

What 2 types of skin lesions may be present?

Answer 1

1* - direct consequence if the disease process
> eg. macule, nodule, tumour, wheal, vesicle, bulla, patch, papule, pustule, comedo, follicular cast, alopecia, scale, crust
2* - evolve from 1* lesion or caused by self trauma (may obscure 1* lesion)
> eg. epidermal colarette, scar, excoriation, erosion, ulcer, fissure, lichenification, hyperpigmentation, callus

Question 2

Define wheals

Answer 2

• discrete focus of dermal oedema

- eg. those seen with intra-dermal skin testing

Question 3

Define angioedema

Answer 3

• more extensive wheal

- oedema affecting whole body region

Question 4

What patterns of inflammation may be seen with skin disease?

Answer 4

• perivascular
• diffuse/interstitial
• nodular
• panniculitis
• interface

Question 5

How does normal skin differ on a single animal?

Answer 5

• haired skin thinner epidermis

- hairless skinner thicker epidermis

Question 6

Define hyperkeratosis

Answer 6

^ stratum corneum, accumulation of loose fragments -> scale

Question 7

Define hyperplasia

Answer 7

^ stratum spinosum (thickening of living cell layer, acanthosis)

Question 8

What are follicular casts and when are they seen?

Answer 8

Accumulation of keratinous debris around the hair shaft

Question 9

Define comedo

Answer 9

• dilated hair follicle plugged with keratinous and sebaceous debris

Question 10

What is perivascular dematitis? How is it classified further?

Answer 10

> stereotypical/classical reaction to a multitude of pathologies! If skin is red and itchy: probably “hyperplastic, superficial, perivasc. derm.”
may be due to allergy/parasites/infection
- prominance of dermal blood vessels
- leucocytes recruited
- usually + epidermal hyperplasia
superficial/deep plexus involved?
predominnat cell type?

Question 11

Define papule. Eg of disease that may cause papules?

Answer 11

• solid palpable skin elevation <1cm diameter

- e g. FAD

Question 12

Define plaque. Which species are these commonly seen in?

Answer 12

• larger, flat-topped elevation caused by extension and coalition of papules
• often seen in horses (viral transmission)

Question 13

Define pustule

Answer 13

Discrete elevation of the epidermis containing pus (cf. abscess dermal/subcut)

Question 14

Define abscess

Answer 14

Demarcated dermal or subcutaneous acumulation of pus (cf. pustule epidermal)

Question 15

Potential causes/pathologies of intraepidermal pustular dermatitis?

Answer 15

> Neutrophilic 
- pyoderma 
- sterile disease eg. pemphigus 
> Eosinophilic 
- ectoparasite infestation 
- hypersensitivity

Question 16

What is erosion?

Answer 16

Decreased thickness of epidermis

Question 17

What is ulceration?

Answer 17

Loss of epidermis down to dermal layer?

Question 18

Define folliculitis

Answer 18

• inflammation of follicle

Question 19

Define furunculosis

Answer 19

• inflammation and destruction of the follicle

+ foreign body reaction

Question 20

Define crust

Answer 20

accumulation of exudate (dead cells and dried serum) on skin surface
- site of previous acive inflammation, epidermal degeneration, pustule etc.

Question 21

What does a papule precede formation of? What will this become?

Answer 21

Pustule -> focal crust or epidermal colarette

Question 22

Which diseases are associated with single lesions?

Answer 22

• dermatophytosis

- cutaneous neoplasia

Question 23

Which diseases are associated with linear lesions?

Answer 23

• external trauma

- blood vessel, dermatome or congential malformation assocaited

Question 24

Which diseases are associated with annular lesions?

Answer 24

• peripheral spreading of disease eg. pyoderma or dermatophytosis

Question 25

What do symetrical lesions indicate?

Answer 25

systmeically mediated disease

Question 26

What is seen with perivascualr inflammation and what diseases is this associated with?

Answer 26

> inflam cells around dermal BVs (Superficial/mid/deep vascular plexus) VERY COMMON! - neutrophils: Self trauma, pyoderma - eosinophils: ectoparasites, hypersensitivty - mononuclear cells: chronic dermatitis, immunologic causes

Question 27

What is the most common cause of an expanding ring like lesion in dogs>

Answer 27

Staph

Question 28

When are comedons often seen?

Answer 28

- demodex - cushings - hypothyroidism

Question 29

What does interstitial derm inflammation indicate?

Answer 29

Diffuse inflammation due to spreading of inflammatory cells from original perivascular patterm

Question 30

What is seen with interface pattern dermatitis and what does this commonly indicate?

Answer 30

> dermo-epidermal junction obscured by inflam cells (lymphocytes) and hydropic degneration of basal keratinocytes > less of pigment possible as melanocytes located near basal cells > vesicles/bullae and erosions/ulcers if epidermal cohesion affected - UNCOMMON, indicates AUTOIMMUNITY against epidermis or DRUG REACTION

Question 31

What does nodular pattern of inflammation indicate? What is seen with this?

Answer 31

``` - inflam celsl in dense clusters, espeically grnaulomatous or pyogranulomatous dermatitis > cell-mediated responses eg: - FB - acid-fast bacilli - deep fungal infection ```

Question 32

What does intra-epidermal vesicular or pustular dermatitis appear as? What causes this?

Answer 32

> vesicles and bullae (blisters) - death of clusters of epidermal cells or loss of adhesion of cells with accumulation of fluid exudate - seen in viral infection eg. FMD > Pustules - inflammatory cells predominate rather than fluid - bacterial infection > +-Acantholysis - destruction of desmosomal attachments between keratinocytes - may be enzymatic eg. proteases in pyoderma - may be autoimmune eg. pemphigus

Question 33

What occours with sub-epidermal vesicular dermatitis? Causes?

Answer 33

> epidermis separates from underlying dermis - newborns with defects in structual proteins -> blistering and ulceration ("mechanobullous disease") - acquired autoimmunity against structual proteins

Question 34

What is folliculutis and what may it be preceded or accompanied by?

Answer 34

- inflammation of the follicle | - perifolliculitis (inflam of adjacent dermis) which may also occour as part of perivascular pattern

Question 35

What is furunculosis?

Answer 35

- inflammatory DESTRUCTION of the hair follicle -> rupture and extrusion of contents (hair, keratin, sebum, infectious agents) into dermis -> Deep pyoderma - 2* FB response often supparative or pyogranulomatous inflammation - > scarring or fistula formation and panniculitis

Question 36

What is atrophic pattern and when is this seen?

Answer 36

- NOT inflammatory pattern - v size of different components of skin - most commonly epidermal thinning + small telogen phase follicles due to endocrine disease

Question 37

What endocrine disorder is seen in "plush coated" breeds?

Answer 37

- castration responsive dermatosis | - > symettrical alopencia and pigmentation

Question 38

What is colour dilution alopecia?

Answer 38

- form of hair follicle dysplasia | - seen in dogs with blue or fawn dilute hair colour (most common blue dobermans)