The cause is unknown but there is an inherited predisposition. The strong genetic influence may result from a single dominant gene with poor penetrance or a number of genetic influences. Other factors such as local trauma, general illness and stress are also involved, so the cause of psoriasis is best regarded as being multifactorial. HLA-Cw6 is the phenotype most strongly associated with psoriasis, particularly the early onset variety in which hereditary factors seem to play the greatest part. There is an increase in HLA expression in psoriatic arthropathy.
Local trauma, acute illness, and stress may be factors in causing the appearance of clinical lesions. p Haemolytic streptococcal throat infection is a common precipitating factor in guttate psoriasis. Antimalarial drugs, lithium, and p blockers can make psoriasis worse. There is evidence that psoriasis occurs more readily and is more intractable in patients with a high intake of alcohol. Smoking is associated with palmo-plantar pustulosis.
Acute arthropathy—X ray signs
There is evidence that both hormonal and immunological mechanisms are involved at a cellular level. The raised concentrations of metabolites of arachodonic acid in the affected skin of people with psoriasis are related to the clinical changes. Prostaglandins cause erythema, whereas leukotrienes (LTB4 and 12 HETE) cause neutrophils to accumulate. The common precursor of these factors is phospholipase A2, which is influenced by calmodulin, a cellular receptor protein for calcium. Both phospholipase A2 and calmodulin concentrations are raised in psoriatic lesions.
T helper lymphocytes have been found in the dermis as well as antibodies to the basal cell nuclei of psoriatic skin. In addition, dermal factors contribute to the development of psoriatic lesions.
The detailed treatment of psoriasis is covered in the next chapter. The only point to be made here is the importance of encouraging a positive attitude with expectation of improvement but not a permanent cure, since psoriasis can recur at any time. Some patients are unconcerned about very extensive lesions whereas to others the most minor lesions are a catastrophe.
Farber EM. Psoriasis. Amsterdam: Elsevier, 1987
Fry L. An atlas of psoriasis. London: Parthenon Publications, 1992
Mier PD, Van de Kerkhof PC. Textbook of psoriasis. Edinburgh:
Churchill Livingstone, 1986 Roenigk HH, Maibach HI. Psoriasis. Basle: Dekker, 1991
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Do You Suffer From the Itching and Scaling of Psoriasis? Or the Chronic Agony of Psoriatic Arthritis? If so you are not ALONE! A whopping three percent of the world’s populations suffer from either condition! An incredible 56 million working hours are lost every year by psoriasis sufferers according to the National Psoriasis Foundation.