Dermatology Made Simple : Psoriasis : Causes

Causes of Psoriasis

Psoriasis is an autoimmune skin disease with an inherited genetic predisposition and immunological triggers.

A psoriasis susceptibility locus PSORS1 is identified on chromosome 21 within the MHC : major Histo Compalibility Complex.

In 60 % of patients,HLA-CW6 is the phenotype associated with Psoriasis especially in patients with early onset disease.

HLA types associated with Psoriatic arthropathy include : HLA B27,B17,CW6,DR4 and DR7.

Trigger factors for Psoriasis:

Certain form of Psoriasis maybe triggered by :

Immunological stimuli such as Beta Hemolytic streptococcal infections.

Certain Drugs:

Antimalarials

Lithium

Beta blockers.

Other factors include:

Local trauma

General illness

Stress

High intake of alcohol

Smoking

Histological changes:

There is increased T cell activity in diseased skin.

The activated T cells lead to high levels of pro-inflammatory cytokines in psoriatic lesions especially gamma interferon and TNF : Tumor Necrosis Factor alpha.

TNF alpha increases keratinocyte proliferation and induces SKALP/elafin gene which is not expressed in normal keratinocytes.

This gene is a marker of abnormal keratinocyte differentiation,a hyperproliferative epidermis and increased inflammation.

The cellular abnormalities found in psoriatic plaques are targeted by some of the novel biological therapies.

TNF alpha blockers include etanercept and infliximab.

T cell blockers include efalizumab and alefacept.