Dermatopathology 1 Flashcards
Skin lesions can be classified based on which characteristics?
- Underlying pathogenetic mechanism E.g. Vasculitis, immune-mediated disorder, inflammatory
- Lesion type (pustules, bullae, folliculitis, etc…)
- Distribution
- Aetiological agents (not always clarified)
What are the 3 embryological layers of the skin?
Outer = ectoderm Middle = mesoderm Inner = endoderm
Describe the anatomy/structure of the skin and its components
- Epidermis
- Dermis, with collagen
- Subcutaneous layer, made up of fat
90% of the cells in the skin are?
Keratinocytes
What other cells types are found in the skin?
- Melanocytes
- Hair follicles
- Sebaceous glands
- Apocrine glands
- Cells with macrophagic function
What are the names of the 3 stages of the hair follicle cycle?
Anagen
Catagen
Telogen
Which part of the hair is the area of proliferation?
Papilla
Loss of keratinocyte cohesion is called?
Acantholysis
Define acanthosis?
Increased thickness of the stratum spinosum (often used to indicate epidermal hyperplasia)
Define alopecia?
Hair loss or failure to grow
Allergic skin disease is termed?
Atopy
Define bullae in the skin
Collection of fluid more than 1cm in diameter
Define folliculitis
Luminal, mural or perifollicular inflammation of the hair follicle
Define furunculosis
Perifollicular inflammation due to hair follicle wall rupture
- Dermal pyogranulomatous inflammation
Increased thickness of the keratin layer is termed?
Hyperkeratosis
What is a skin pustule?
Cavitation of the epidermis filled with inflammatory cells
Melanin granules and melanophages within the dermis is termed what?
Pigmentary incontinence
Define seborrhoea
Increased scale formation with or without excessive greasiness
Epidermal intercellular oedema is termed?
Spongiosis
A fluid filled blister of more than 1cm in diameter is called a?
Vesicle
What is Ki67 a marker of? (found in the nucleus of keratinocytes)
Indicates active cell division of the basal layer of the epidermis
- this is a normal finding on immunohistochemistry
What do black granules seen on immunohistochemistry represent?
Production of melanocytes
What is the function of melanocytes?
Repair and protect the nucleus of keratinocytes from UV light
What is the function of Langerhans cells?
Mononuclear
Dendritic
Antigen presenting cells of the epidermis
What are desmosomes?
Proteins that keep one cell (keratinocyte) attached to another
Basal keratinocytes are firmly adherent to the basal lamina via?
Hemidesmosomes
How would a pustule appear histologically?
As aggregates of neutrophils between keratinocytes on the surface of the epidermis
Name a vascular skin disease of pigs
Diamond skin disease
- venous infarct lesions of the skin
What are 3 causes of vasculitis?
- Endotheliotropic organisms
- Deposition of immune complexes
- Septic emboli
How does vasculitis appear grossly?
- Haemorrhagic
- Erythematous plaques, macules, purpura, oedema and ulcers
- Chronic lesions: ulcers and dermal atrophy
- Marked predilection for extremities (ear pinnae, lips and tail) – bits missing
Define the following:
- Macule
2. Purpura
- a flat, distinct, discoloured area of skin
2. Purple discoloured coloured spots on the skin
Describe the histological hallmark of vasculitis
Karyorrhectic cell debris (Leukocytoclastic) and fibrinoid necrosis of the vessel wall surrounded by fibrin exudation and haemorrhages
Neutrophilic vasculitis is suggestive of?
A type III hypersensitivity reaction or septicaemia
A cell mediated immune response causes which type of vasculitis?
Lymphoplasmacytic vasculitis
Eosinophilic vasculitis is suggestive of?
A type I hypersensitivity reaction or other eosinophil-dominated dermatoses (e.g. eosinophilic granuloma)
A superficial bacteria pyoderma is restricted to which part of the skin?
The dermis
What is impetigo?
Superficial pustular dermatitis with no involvement of the hair follicle
Describe the gross and histological features of impetigo
Gross: erythematous with papules that become pustules
Histo: subcorneal pustules composed of neutrophils
What is the differential diagnosis for impetigo?
Pemphigus foliaceous
- no prominent acantholysis occurs in impetigo
‘Greasy pig’ is called?
Exudative epidermitis of pigs
Exudative epidermitis of pigs affects which age and is caused by?
Acute superficial exudative pyoderma of young (5-35 days) pigs caused by Staphylococcus hyicus
What are the features of exudative epidermitis of pigs?
- High morbidity and mortality
- Exotoxin produces cleavage between the stratum corneum and granulosum
How does exudative epidermitis of pigs appear grossly?
Greasy dark brown exudate over eyes, snout, chin and ears which can spread over the body
How does exudative epidermitis of pigs appear histologically?
Subcorneal pustular dermatitis
- epidermis covered with ortho- and parakeratotic hyperkeratosis, serum, neutrophils and bacterial colonies
Describe the 3 clinical forms of exudative epidermitis of pigs?
- Acute - rapid spread to the whole body and death in 3-5 days
- Subacute - lesions confined to the head and high percentage of surviving piglets
- Chronic - High survival rate but poor growth
Dermatophilosis is caused by which bacteria?
Dermatophilus congolensis
- Gram positive coccoid bacterium producing branching filaments
What are the favourable conditions for Dermatophilus congolensis growth?
Skin trauma + a wet skin environment
Describe the lesions caused by Dermatophilus congolensis?
Continuous and cyclic epidermal invasion, inflammation and regeneration causes thick parakeratotic crusts
Which bacterial spp is most commonly involved in deep pyoderma?
Staphylococcus spp
Describe the gross appearance and progression of lesions due to Staphylococcus spp (deep pyoderma)
Follicular papula -> pustule -> crust formation and coalescing ulcers and alopecia -> dark red nodules, ulcers and fistulae -> lymphadenopathy and fever -> epidermal acanthosis
Describe the histological appearance and progression of Staphylococcus spp (deep pyoderma)
Neutrophilic folliculitis (inflammation of the hair follicles) and furunculosis (inflammation caused by the disappearance of the hair follicle and the release of keratin) with bacterial colonies -> free keratin fragments (keratin scales) -> foreign body reaction and haemorrhages - Suppurative inflammation with intracellular bacteria
What are the entry routes of abscesses and cellulitis?
Contaminated wounds or contaminated foreign bodies
What are abscesses and cellulitis associated with?
Fever and lymphadenopathy
Define abscesses and cellulitis
Focal non-specific severe suppurative inflammations of the deep dermis and panniculum
How does an abscess appear histologically?
Circumscribed central core of necrotic material and degenerate neutrophils surrounded by a granulation tissue-like reaction
How does cellulitis appear histologically?
Poorly circumscribed extensive suppurative or pyogranulomatous inflammation with oedema, haemorrhage and thrombosis
Cutaneous bacterial granulomas are caused by?
- Actinomyces or Nocardia spp
- Mycobacteria infections e.g. M. tuberculosis and bovis
A Cutaneous bacterial granulomas caused by Actinomyces or Nocardia spp has what gross features?
- Pyogranulomatous dermatitis and panniculitis
- Grossly: large fibrotic and ulcerated nodules, often with draining fistulous tracts (sulphur granules)
How do sulphur granules appear histologically?
Masses of basophilic to amphophilic organisms bordered by bright eosinophilic material
Name 3 examples of viruses that affect the skin
- Poxviruses
- Herpes viruses
- Papilloma viruses
What is a poxvirus?
A DNA virus with high epitheliotropism that is responsible for numerous primary skin diseases
Name some examples of poxviruses
- Cowpox virus
- Bovine papular stomatitis
- Orf virus
Poxviruses are capable of causing which 2 lesion types?
Vesicular and proliferative lesions
How are the gross lesions of cowpox distributed and how do they appear?
- Single distribution with predilection for face and forepaws
- Ulcers -> papules and pustules in secondary lesions
Describe how coxpox appear histologically
- Focal sharply demarcated ulcer covered in fibrinonecrotic exudate
- Large eosinophilic intracytoplasmic inclusion bodies in epidermal and follicular epithelia
Describe the Features of Orf
- Contagious pustular dermatitis
- High morbidity, low mortality
- Predominantly affects lambs and kids
How are the gross lesions of Orf distributed and how do they appear?
- Distribution: starting from lip commissure -> lips and muzzle -> legs (rare)
- Appearance: Multifocal to coalescing raised and flat grey crusts
How does Orf appear histologically?
Ballooning degeneration and spongiosis with prominent epidermal hyperplasia and crust formation
Herpes virus dermatitis is caused by which virus in cats?
Feline herpes virus type 1
How are the gross lesions of herpes virus dermatitis distributed and how do they appear?
Distribution: Primarily on nasal planum and haired skin of the face
Appearance: Persistent and recurrent crusts, ulcers and vesicles
How does herpes virus dermatitis appear histologically?
Ulcerative and necrotising dermatitis, large intranuclear glassy inclusion bodies and mixed dermal infiltration
