Dermatopathology 2 Flashcards
Mycoses affecting the skin can be divided into which 3 types?
- Cutaneous
- Subcutaneous
- Systemic
Describe cutaneous mycoses and give 2 examples
- The most common mycoses types
- Confined to the cornifies tissues
- E.g. Malassezia dermatitis and Dermatophytosis
Describe subcutaneous mycoses
Huge variety of saprophytic fungi, remain localised
Describe systemic mycoses and name example causes
Haematogenous dissemination (e.g. Cryptococcus, Blastomyces, Coccidioides spp)
What is Dermatophytosis?
Superficial mycotic infection (“ringworm”) confined to the keratin layer of skin, claws and hair.
What are the 3 favourable conditions for Dermatophytosis?
- Microabrasions or maceration of the stratum corneum in moist skin
- Prolonged corticosteroid treatment
- Transient or permanent immune deficiencies
How is Dermatophytosis transmitted, how does it then cause infection?
- Via infected hair and keratin fragments
- Fungi migrate to the follicular lumen and proliferate along the entire follicle
How are Dermatophytosis lesions distributed?
Head and extremities
How do Dermatophytosis lesions appear grossly?
Gross: Circular expanding areas of scaling and alopecia. Often furunculosis and chronic pyogranulomas (kerion) develop and mimic tumours
First appears as a red colour and as the epidermis thickness (thickened keratin layer) increases the colour becomes greyish – this is the infectious part as it is covered in fungal spores
How does Dermatophytosis appear histologically?
Hyperkeratosis and acanthosis.
Luminal folliculitis, furunculosis and pyogranulomas.
Fugal spores lining the hair shaft.
Fungal hyphae admixed with serous crusts of the epidermal surface.
Describe the features of Leishmania parasite
- Causes skin and systemic lesions
- Obligate intracellular apicomplexan parasite of macrophages
- Transmitted by blood sucking sand flies
Describe the two clinical forms of Leishmania
Alopecic: stronger Th1 response and fewer parasites
Nodular: predominant Th2 response and more numerous parasites
Describe the gross lesions distribution and appearance of Leishmania
Distribution: head, limbs and dorsal midline
Appearance: Variable. Nodules, alopecia, ulcers or pustules. Bilateral.
Describe the histological appearance of Leishmania
Hyperkeratotic, nodular to diffuse superficial and deep granulomatous dermatitis, variably dominated by plasma cells.
What is Myiasis?
The infestation of living tissues by the larval stages of dipterous flies
Describe how some dipterous spp migrate?
- Some remain localised to the site of injury with limited local penetration
- Others migrate from the wounded skin or the GI tract after ingestion and colonise -> development of cyst-like dermal structures with a central pore -> emerge from the pore and pupate in the environment
Describe inflammation associated with myiasis
Eosinophilic and lymphocytic inflammation (along migration tracks) and fibrous capsule with eosinophils and granulation tissue in the cystic dermal cavity
Name some examples of parasites that cause myiasis
- Hypoderma bovis and H. Lineatum : cattle (warble)
- Blowflies (lucilia, calliphora, etc): sheep
Sarcoptic mange is caused by which parasite?
Sarcoptes scabei
What are some features of sarcoptic mange
- Zoonotic, highly contagious and notifiable disease
- Extremely pruritic
- Common in pigs and dogs
How are sarcoptic mange lesions distributed?
Inner surface of the pinna, spreading to head, neck and legs
Where does Sarcoptes scabei live in the skin?
The parasite lives between the keratinocytes – it doesn’t go into the dermis it only lives within the dermis
Describe the histological appearance of sarcoptic mange
Severe acanthosis, parakeratosis, spongiosis, leukocyte exocytosis, eosinophilic pustules
Where do Demodex mites complete their life cycle?
Within the lumen of hair follicles
Describe the gross lesion appearance of Demodectic mange
Alopecia, scaling and comedones in the squamous form; pustules, folliculitis and furunculosis in pustular form (complicated by bacteria)
Describe the gross lesion distribution of Demodectic mange - localised and generalised forms
Localized form: Well-circumscribed self-limiting lesions on ears, lips, eyes and extremities
Generalized form: diffuse alopecia and scaling (face and legs)
Describe the histological lesion appearance of Demodectic mange
Severe suppurative folliculitis and furunculosis (deep infection of the hair follicle leading to abscess formation with accumulation of pus and necrotic tissue)
Give some examples of traumatic and chemical injuries
- Mechanical forces
- Hot temperatures/burns
- Primary irritant contact dermatitis
- Photosensitisation
What are bruise?
The local effect of vigorous pressure (blunt trauma) can cause the occurrence of acute intradermal and/or subcutaneous haemorrhages
What are the 3 molecular components of a bruise as it heals?
Haemoglobin -> biliverdin -> bilirubin
How does a bruise occur?
- Lesion will evolve rigorously following the steps of erythrocyte removal (recruited leukocytes and phagocytes) and haemoglobin catabolism (typical lesion colour)
- Haemosiderin-laden macrophages can remain visible locally for a very long period of time after clinical resolution of the trauma
What are the 3 types of blood discolouration?
- Petechia (1mm)
- Purpura (up to 1cm, coalescing petechiae)
- Ecchymosis (> 1cm)
How does haemorrhage resolution occur?
Incoming macrophages phagocytose extravasated erythrocytes
Explain the steps involved in a bruise becoming yellow over time
3 – days after a bruise has occurred, inflammatory cells produce Haemosiderin because Hb produced by erythrocytes isn’t going anywhere, only macrophages can clear it, they keep the iron from Hb and the rest of it becomes bile (why a bruise becomes yellow over time)
Define hypersensitivity
Any excess of immune response targeting an antigen from the outside world that would normally be unharmful to most of the population
Give 4 examples of hypersensitivity reactions
- Urticaria
- Atopic dermatitis
- Food hypersensitivity
- Insect hypersensitivity
Define autoimmunity
Pathological immune reaction against self-antigens
Name some examples of autoimmune reactions
- Pemphigo-complex diseases
- Bullous pemphigoid
- Lupus erythematosus
- Erythema multiforme
- Alopecia areata
Why keratinocyte type make up most of the population?
Spinous keratinocytes
Which layer of keratinocytes lies beneath spinous keratinocytes? What is their function?
Tiny cuboidal cells = basal keratinocytes – these continually proliferate
Describe the top layer of the epidermis
The top layer is much flatter and contains a lot of granules which lead to the formation of keratin which is the final layer called the stratum corneum
Describe the mechanism of action of hypersensitivity reactions
- Macrophages (that liver permanently in the skin) are exposed to the antigen
- They educate immune cells from the lymph node that arrive in the skin and lead to the production of immunoglobulins from plasma cells (IgE)
- These attach themselves to muscles and lead to oozing of the muscle contents and blood (eosinophils)
What is the name given to the mildest hypersensitivity reaction?
Urticaria
How is urticaria characterised?
The oozing of a very protein poor fluid from the holes between endothelial cells - caused by the release of granules from muscles
Describe the features of urticaria
Acute, variably pruritic, oedematous skin lesions -> Type I hypersensitivity reaction
What are the causes of urticaria
- Caused by mediators of basophils and mast cells
- Drugs, foods and food additives are frequent causes
Describe the gross lesion distribution and appearance of urticaria
Distribution: variable, localised to widespread
Appearance: Discrete, well-circumscribed round erythematous and oedematous plaques
Describe the histological appearance of urticaria
Variable and non-specific.
Subtle or prominent dermal oedema of the superficial dermis
What is the cause of atopic dermatitis?
Increased production of IgE against “innocuous” antigens
Atopic dermatitis is common in which spp?
West Highland terriers
How does atopic dermatitis present clinically?
Intense pruritus (due to large eosinophil numbers)
Describe the gross lesion distribution and appearance of atopic dermatitis
Distribution: Variable, but typically on the ventral sparsely-haired skin (head, paws, distal extremities and ventrum)
Appearance: excoriations, papules, pustules, hyperpigmentation and lichenification are considered secondary to trauma induced by pruritus
Describe the histological appearance of atopic dermatitis
Perivascular to interstitial lymphoplasmacytic dermatitis with oedema, eosinophils, macrophages and variable degree of epidermal hyperplasia
Where do antigens causing insect hypersensitivity come from?
Insect saliva, venom, whole body or faeces
Insect hypersensitivities are which 2 classes of hypersensitivity reaction?
I and IV
What are 2 examples of insect hypersensitivity reactions?
- Flea-bite hypersensitivity: (“flea allergic dermatitis”)
- Culicoides hypersensitivity: horses (“sweet itch”).
Describe the gross lesion distribution and appearance of insect hypersensitivity reactions
Distribution: Sparsely haired body regions. Lumbosacral region for flea-bite hypersensitivity
Appearance: Pruritic crusted papule -> hyperkeratosis, lichenification, seborrhoea and excoriation (secondary lesions)
Describe the histological appearance of insect hypersensitivity reactions
Eosinophil dominated dermal perivascular to diffuse dermatitis with lymphocytes and fewer macrophages
Describe the gross lesion distribution and appearance of Pemphigus foliaceus
Distribution: restricted to the skin (no mucosa). Starts from periocular and nasal skin (cat, dog) -> ears, neck and ventral abdomen
Appearance: erythematous maculae -> pustules -> erosion and crusts
Describe the histological appearance of Pemphigus foliaceus
Acantholytic (loss of cohesion between keratinocytes) subcorneal or intragranular pustular dermatitis
Name the two forms of lupus erythematosus
- Systemic lupus erythematosus (SLE)
- Discoid lupus erythematosus (DLE)
Describe the gross lesion distribution and appearance of Discoid lupus erythematosus
- Restricted to the nasal planum
- Erythema, depigmentation, scaling, crusting, alopecia and ulcers
Describe the histological appearance of Discoid lupus erythematosus
Epidermal hyperplasia, denser interface infiltrate dominated by lymphocytes (few plasma cells)
