Case 8- psoriasis and eczema Flashcards
Psoriasis
A chronic inflammatory skin condition characterised by scaly plaques (areas of thickened skin). The most common psoriasis is chronic plaque psoriasis (90%) you also have guttate psoriasis
Who does psoriasis effect?
Effects 2-4% of the population with equal amounts of males and females. More common in Caucasians but effects any race
What causes psoriasis- vague
The pathophysiology is complex and not fully understood. There is a strong genetic element but also some environmental triggers i.e. stress, smoking and certain medication. The triggers can lead to a flare up. It is an autoimmune response which results in hyperproliferation of keratinocytes.
Mechanism of action of psoriasis
- Stimulus: genetic susceptibility/environmental trigger.
- T cells and dendritic cells infiltrate the skin
- There is release of pro-inflammatory mediators i.e. TNF, IL-7
- Activation and proliferation of keratincoytes
- Keratinocytes are proliferating more quickly and move up through the epidermis in 3-5 days, normally it takes 21 days.
- This results in a thick epidermis and scaly skin as it flakes of
When does psoriasis present?
It presents for the first time in people under 35 but is uncommon in children
What does psoriasis effect?
It has a relapsing course and is quite persistent but can improve with treatment. It tends to affect the scalp and extensor surfaces (particularly knees and elbows), it is usually symmetrical.
The lesions of psoriasis
The lesions themselves are elevated areas of thickened skin known as plaques. They are usually well-demarcated and circular/oval in shape. They can be red-pink or dark brown/purple in colour. They have an overlying white, silvery or grey scale. They are usually very itchy.
Psoriasis changes associated with nails
- Pitting of the nail
- Yellowing of the nail
- Onycholysis- separation of the nail from the nail bed.
Guttate psoriasis
Characterised by multiple small scaly plaques, looking like multiple small teardrops on the body. Mostly affects the trunk, upper arms and thighs. It often 2-3 weeks after a streptococcal infection of the upper respiratory tract i.e. tonsilitis, pharyngitis. It usually spontaneously resolves after 3-4 months, although another flare-up can occur following another streptococcal infection.
Clinical consequences of psoriasis
It is associated with significant psychosocial difficulty. Quality of life can be severly affected by sever itching, dry/peeling skin and side effects of treatment. The lesions can be widespread leading to patients becoming self-conscious about their appearance, this can lead to anxiety and depression
Conditions psoriasis is associated with
Psoriatic arthiritis, inflammatory bowel disease, metanolic syndromes (central obesity, hypertension, insulin resistance).
Eczema
Also known as atopic dermatitis, is a chronic inflammatory skin condition that is characterised by dry, itchy and inflammed areas of skin. Very common in children, 80% of cases present before 5. It has a complex pathophysiology with no single known cause. Overall it is a result of a weakened skin barrier and predisposition torwards allergic inflammation. This predisposition is atopy.
How do allergens get through the skin
Through the small pores of the skin, this triggers a hypersensitivity reaction
Mechanism of eczema
- An environmental allergen gets through the skin barrier
- The allergen gets picked up by an antigen presenting cell (dendritic)
- This activates a T helper cell which stimulates the B cell to produce IgE antibodies that are specific to the allergen.
- The IgE antibody binds to a mast cell or basophil, resulting in sensitisation.
- When there is a second exposure to the allergen, the allergen can bind to the IgE antibodies on the surface of the mast cell/basophil.
- This binding causes the mast cell/basophil to release pro-inflammatory molecules i.e. histamine
- This causes dilation of blood vessels (redness) and increased permeability of the skin barrier so more allergens can enter and water is lost from the skin
Eczema- what happens when water is lost from the skin?
The water loss causes dry skin which is very itchy, when the patient itches their skin they further damage and breakdown the skin barrier. More allergen is able to get in and the cycle continues.
The two factors that lead to eczema
1) Skin barrier failure
2) Role of the immune system
Unclear whether the main cause of eczema is the imbalance in the immune system or the reduced production of fiaggrin
Eczema- skin barrier failure
A genetic mutation leads to less production of the protein filaggrin (needed to help create corneocytes and the lipid matrix from keratinocytes). This leads to a failure of the skin barrier as its more permeable so more allergens are able to enter and provoke an immune response. More water is also able to leave the skin
Eczema- role of immune system
Some patients have increased levels of T helper cells due to a genetic mutation. This causes a stronger immune response to allergens so increases inflammation