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Psoriasis affects 1 to 5 p. 100 of the population depending on the regions of the world, but it is difficult to estimate the percentage precisely because many patients do not treat their symptoms, either because they consider that the treatments cause more discomfort than the disease itself, or through discouragement.
Uncomplicated psoriasis plaques are red, typically covered with micaceous scales. Removal of the scales with a curette leads to redness and bleeding. The scales which are always present may differ considerably in appearance. They may be ostreaceous, forming a helmet on the scalp, for example, or scurfy, closely resembling those observed in patients with seborrhoeic dermatitis.
Psoriasis is characterised histologically by acanthosis and papillomatosis, indicative of excessively rapid renewal of the epidermis, associated with a differentiation disorder leading to continuous or discontinuous parakeratosis.
These abnormalities are associated with inflammatory cell infiltration at a very early stage of plaque development. The cell infiltrate originally consists of polynuclear neutrophils, which often accumulate to form micro-abscesses under the horny layer of the epidermis leading to major alterations of the membranes of the keratinocytes in the vicinity due to the release of lysosomal enzymes. These alterations permanently activate epidermal renewal. The other cells making up the infiltrate of the skin lesions consist of T lymphocyte subpopulations, particularly CD4 cell in the dermis and CD8 cells in the epidermis. The T lymphocytes play a major role in the pathophysiology of psoriasis although it is not known which roles the CD4 and CD8 cells play respectively, or how they participate in the maintenance of local inflammation and hyperproliferation.
Histologically, the lesions may be atypical in some areas of the body, particularly the palms of the hands or soles of the feet where spongiosis is often observed. Therefore, it is pointless to perform a skin biopsy to differentiate between psoriasis and eczema on the palms of the hands or soles of the feet.
NATIONAL PATIENTS ASSOCIATIONS
Fundacion de Apoyo al Paciente con Psoriasis (FUNDAPSO)
REPUBLIC OF KOREA
Psoriasis Philippines (PsorPhil)
www.papaa.org (psoriasis and psoriatic arthritis alliance)
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