Skin Pathology 1 Flashcards
-Outline structure and function of the skin and the importance of dermatology in veterinary medicine. -Explain the concept of patterns of skin disease in relation to epidemiology, clinical presentation, histopathology. -Give examples of how breed, sex, geographical location, and time of year may influence the incidence and prevalence of skin disease. -Explain, with examples, how macroscopic pathology of skin lesions may provide a clue to pathogenesis or aetiology. -Explain, with examples
WHY STUDY THE SKIN?
Largest organ in the body.
Provides crucial defence from environment.
Skin problems VERY common in small animal practice (1 in 5 consultations).
Skin disease is a major cause of morbidity and economic loss in farm animals worldwide.
Animal disease provides insights and models for human disease.
STRUCTURE OF THE SKIN
Epidermis- basal, spinous, granular, cornified layers (deep to superficial), basal cells.
Basal layer contains dendritic Langerhans cells, melanocytes,
Dermis- cells, fibres, matrix (ground substance), vascular supply and innervation- sensitive.
Apoliposebaceous complexes- hair follicles and associated sweat (apocrine) and sebaceous glands.
Hypodermis (subcutis, panniculus)- fat and fibrous tissue.
Compound hair follicles seen in carnivores.
FUNCTION OF THE SKIN
-Physical protective barrier
-Immunity- skin immune system
-Thermoregulation
-Blood pressure regulation
-Sensory perception
-Secretions (communication)
-Storage (fat etc)
-Vitamin D production (especially herbivores)
The skin barrier is self repairing.
PATTERNS OF SKIN DISEASE
- EPIDEMIOLOGY- breed, sex, location, season.
- CLINICAL PRESENTATION- lesions, distribution, configuration.
- HISTOPATHOLOGY- pattern analysis.
PATTERNS OF SKIN DISEASE- EPIDEMIOLOGY
eg. BREED- skin fold dermatitis (intertrigo) in Sharpei, Bulldog, Pekingese.
SEX- symmetrical alopecia- particular distribution due to oestrogen production in by Sertoli cell tumours in male dogs (especially cryptorchids)
LOCATION- cutaneous hemangiosarcoma due to sun exposure in dogs in West Indies, Grenada.
SEASON- flea allergy dermatitis- more common in temperate climates, seen year round. Seen truly seasonally in colder climates. Lesions often due to self trauma from itchiness.
PATTERNS OF SKIN DISEASE- CLINICAL PRESENTATION
Clinical signs relate to macroscopic pathology. Lesion DISTRIBUTION (location), DESCRIPTION (size, shape, colour, consistency, location), lesion TYPE eg. inflammatory, hyperplastic, alopecic, hypertrichotic, tumoural/neoplastic (nodular- not all nodules are neoplastic!)
LESION DISTRIBUTION DIAGRAMS
Used to illustrate distribution of lesions.
Some skin diseases have characteristic lesion patterns.
eg. Ventral lesions, edges of ear- sarcoptic mange.
eg. More irregular, dorsal lesions, muzzle/front paws of puppies- demodectic mange.
PRIMARY SKIN LESIONS
Develop spontaneously as a result of underlying disease.
Useful in trying to determine pathogenesis and aetiology of disease.
Biopsying EARLY will help to determine primary skin lesions.
-MACULE or PATCH (patch if >1cm)
-PAPULE or PLAQUE (if >1cm)
-VESICLE or BULLA (>1cm)
-PUSTULE or ABSCESS (more complicated than pustule)
-WHEAL or ANGIOEDEMA (massive oedema)
-CYST
-NODULE (1-2cm) or TUMOUR (>2cm)
MACULE
A circumscribed, NON PALPABLE spot characterised by a change in the colour of the skin.
No change in consistency of skin.
A macule larger than 1cm is called a PATCH.
PAPULE
A small, solid ELEVATION of skin, less than 1cm diameter. Palpable- usually reflects accumulation of cells/fluid in an inflammatory reaction.
Macules and papules commonly present together- maculopapular reaction.
PLAQUE
A large (>1cm) FLAT TOPPED elevation, formed by extension or coalescence of papules.
NODULE
A circumscribed, solid elevation, less than 1cm diameter.
Usually caused by massive cell infiltration, that may be inflammatory or neoplastic.
TUMOUR
A mass of more than 2cm that, strictly speaking, may be neoplastic or non-neoplastic (eg. granulomatous), though the term is often used to imply neoplasm.
PUSTULE
May be intraepidermal, subepidermal, or follicular. Typically contain neutrophils and bacteria, but may contain eosinophils and/or be sterile.
Tend to be transient in animals- may only see a ‘popped’ pustule.
ABSCESS
A deep, localised accumulation of pus in an are of tissue destruction, surrounded by inflammation.
Usually more deeply located than a pustule.
VESICLE or BULLA
Sharply circumscribed epidermal elevation filled with clear fluid. May be intraepidermal or subepidermal.
Bulla- similar to a vesicle, but larger than 1cm diameter.
Fragile lesions.
WHEAL (HIVE)
A circumscribed, raised lesion due to oedema, often transient. Localised.
ANGIOEDEMA- more severe/deep/extensive oedema. Can reach the dermis/subdermis.
CYST
An EPITHELIUM LINED cavity, containing fluid or solid (inspissated) material. Smooth, well circumscribed, usually fluctuant (move when pressed).
DIFFERENTIAL DIAGNOSIS OF MASS LESIONS
- Abscess
- Granuloma
- Cyst (simple? Parasitic?)
- Neoplasm
- Haematoma- a collection of blood cells can present as a mass lesion.
SECONDARY SKIN LESIONS
Evolve from primary lesions or are induced by self trauma or external factors. Secondary lesions complicate the clinical picture and make diagnosis difficult. -EPIDERMAL COLLARETTE -EXCORIATION -EROSION or ULCER -FISSURE -SCAR -LICHENIFICATION -CALLUS
COLLARETTE
A circular rim of scale (loose or peeling keratin) that evolves from a pustule, vesicle or bulla.
More commonly seen than the primary lesions that lead to them- pustules, vesicles and bullae are fragile, transient lesions.
If a collarette is found, look for an intact pustule to allow biopsy.
EXCORIATION
Erosions or ulcers caused by SELF TRAUMA ie. scratching, rubbing or biting. Typically linear in conformation, they generally indicate PRURITIS.
Can sometimes be an indication of pain.
EROSION
A shallow epidermal defect that does not penetrate the basement membrane and thus heals by regeneration, without scarring.
ULCER
An epidermal defect that reaches deep enough to expose the underlying dermis. Results from a deep pathological process and heals by deposition of fibrous connective tissue and scar formation.
FISSURE
A linear cleavage of epidermis, may also include dermis, due to disease or injury, that appears as a sharply defined cleft or multiple small cracks.
Particularly seen in footpads- dried, dessicated skin.
SCAR
Connective tissue repair of dermal injury results in fibrous tissue that replaces normal skin components.
Connective tissue is deposited parallel to skin surface to maintain skin tension.
LICHENIFICATION
Thickening and hardening of the skin produces exaggerated skin markings (wrinkles etc.). Typically due to friction; areas may be hyperpigmented due to reaction of melanocytes.
CALLUS
A localised area of rough, thickened, hyperkeratotic skin forming an alopecic, often lichenified plaque. Due to long term friction eg. elbow patches in outdoor dogs.
LESIONS THAT MAY BE PRIMARY OR SECONDARY
- ALOPECIA
- SCALE
- CRUST
- FOLLICULAR CASTS
- COMEDONES
- PIGMENT ALTERATION
SCALE
An accumulation of keratinised cells. Normal loss of keratinised cells is not visible to the naked eye; scale is abnormal.
May be thick, thin, dry or oily- depends on the animal, location and underlying cause.
CRUST
Formed from dried exudate (serum, blood, cells, scales) that adheres to the skin surface.
Commonly blood and serum- exudative dermatitis.
COMEDONES
Singular- COMEDO.
A plug of cornified cells and sebaceous material within the dilated lumen of a hair follicle.
Follicular casts are ‘microcomedones’
FOLLICULAR CASTS
An accumulation of keratinous debris that adheres to the hair shaft and protrudes from the follicle ostium on to the skin surface.
PATTERNS OF SKIN DISEASE- HISTOPATHOLOGY
Pattern analysis. Skin biopsy interpretation depends on:
- Location and distribution of lesions (eg. lesions around blood vessels are commonly seen, as cells have entered the skin via haematogenous spread).
- Type of change and cells involved.
- Likely pathogenesis of the observed changes- what has happened to cause these changes?
TYPE OF DISEASE
MINIMAL, MILD or SEVERE.
Consider epidemiology, clinical presentation, histopathology.
Chronicity? HOW LONG HAVE THE CHANGES BEEN GOING ON- the condition may have become secondary by the time the owner notices.
