Histo: Skin Pathology Flashcards
How thick is a normal epidermis, dermis and subcutaneous fat put together?
6 mm
What types of fibres are found in the layer underneath the epidermis?
Collagen
Elastic fibres
What structures are found within the dermis?
- Blood vessels
- Sweat glands
- Hair follicles
- Sebaceous glands
- Nerve fibres
How is palmar-plantar skin different from skin in other parts of the body?
There are no sebaceous glands
There is a very thick corneal layer
Describe the effects of ageing on the skin.
Skin becomes fragile with very little epidermis
Collagen and elastic fibres are of poor quality
List some different types of inflammatory reaction patterns in the skin.
- Vesiculobullous - forms bullae
- Spongiotic - becomes oedematous
- Psoriasiform - becomes thickened
- Lichenoid - forms a sheeny plaque
- Vasculitic - associated with vasculitis
- Granulomatous - associated with granulomas
What is bullous pemphigoid? Describe the macroscopic appearance.
- Vesiculobullous condition
- Occurs in elderly patients on their flexor surfaces
- Characterised by the formation of tense bullae
NOTE: it has a 10-20% mortality
Outline the pathophysiology of bullous pemphigoid.
- Autoimmune disorder driven by IgG and C3 which attack the basement membrane
- They recruit eosinophils which release elastase which further damages anchoring proteins (anchoring lower keratinocytes to the basement membrane)
How can bullous pemphigoid be definitively diagnosed?
Immunofluorescence will show IgG and C3 along the dermo-epidermal junction
Describe the macroscopic appearance of pemphigus vulgaris.
Blisters are flaccid meaning that they rupture easily exposing a red raw surface underneath
Outline the pathophysiology of pemphigus vulgaris.
IgG-mediated disease where the damage is occuring within the keratinocyte layers
What is acantholysis?
- Loss of intercellular connections leading to loss of cohesion between keratinocytes
NOTE: this can occur due to a lot of dermatological conditions so immunofluorescence is needed to identify where the immune-mediated attack is taking place
Describe the macroscopic appearance of pemphigus foliaceus.
- You rarely see intact bullae because they are so thin and fragile
- You are likely to see some flaky remnants of old bullae
Outline the pathophysiology of pemphigus foliaceus.
IgG-mediated attack on the outer layer of keratinocytes (where the stratum corneum is found)
Describe the appearance of discoid eczema.
- Very itchy and found on the flexural surfaces
- Presents with discoid plaques
Describe the clinical presentation of contact dermatitis.
- Itchy erythematous rash usually on the hands or feet (areas most commonly exposed to irritants)
What is hyperparakeratosis?
- Thickening of the skin on the surface where the patient has been scratching
- The epidermis gets thicker
What type of inflammatory skin reaction is eczema?
Spongiotic because there is oedema between the keratinocytes
What are the main immune mediators in eczema?
- T cell mediated
- Eosinophils are also recruited
NOTE: this pattern is also seen in drug reactions
Describe the typical presentation of plaque psoriasis.
- This is a psoriasiform reaction pattern
- Tends to present as silvery plaques on the extensor surfaces
How is the keratinocyte turnover time different in psoriasis compared to normal skin?
- Normal skin turnover = 50 days (time for keratinocyte to go from the bottom of the epidermis to the top)
- Psoriasis = 7 days
- This leads to thickening of the epidermis and you get a layer of parakeratosis at the top
Which layer of the epidermis disappears in plaque psoriasis and why?
Statum granulosum - there is not enough time to form it
What can neutrophil recruitment to the epidermis in plaque psoriasis cause?
Formation of Munro’s microabscesses
What is lichen planus and what are its main features?
- Lichenoid reaction pattern
- T-cell mediated
- Presents with papuls and plaques that are slightly purplish in colour on the wrists and arms
- In the mouth it presents as white lines (Wickham striae)
Describe the histological appearance of lichen planus.
- Distinction between dermis and epidermis is difficult to see due to lymphocyte-mediated destruction of the bottom layer of keratinocytes
- There is band-like lymphocytic infiltration just under the epidermis
NOTE: this is also seen in mycosis fungoides
What type of inflammatory skin reaction results in pyoderma gangrenosum?
Vasculitic
Describe the classic macroscopic appearance of seborrhoeic keratosis.
‘Stuck on’ appearance
Which histological feature is classic of seborrhoeic keratosis?
Horn cysts - entrapped keratin surrounded by proliferating epidermis
NOTE: the epidermis is proliferating in an ordlerly manner
Describe the appearance of sebaceous/epidermal cyst.
- Smooth surface
- Non-mobile
- Tend to have a punctum
- Can get infected/rupture
- Can smell really bad
Describe the histological appearance of a sebaceous cyst.
- Looks like the surface has become invaginated to form a cyst
- Lined by squamous epithelium
Describe the macroscopic appearance of a basal cell carcinoma.
Rolled, pearly edge with a central ulcer and telangiectasia
Describe the histological appearnace of a basal cell carcinoma.
- Cancer arises from the keratinocytes along the bottom of the epiderms (basal cells)
- They can infiltrate through the basement membrane
- They are locally infiltrative but don’t metastasise
What is Bowen’s disease?
Squamous cell carcinoma in situ
Describe the histological appearance of a benign junctional naevus.
- Melanocytes expand in their normal position sitting on the basal layer and form nests
- They are circumscribed and uniformly pigmented
Describe the normal migration of melanocytes as they mature.
As they mature they become smaller and go deeper
What are some clinical signs suggestive of a malignant melanoma?
- Assymetry
- Border irregularity
- Colours
- Diameter
- Evolution
Describe the histological appearance of malignant melanoma.
- Melanocytes start migrating upwards through the epidermis (pagetoid spread)
- They become active and lose the ability to differentiate
- Melanoma thickness > 4 mm has a > 50% mortality
