What Causes Psoriatic Arthritis

It is not yet known what causes psoriatic arthritis.

However, hereditary factors, environmental factors and immunological factors play a role.

Hereditary:

40% of patients with psoriatic arthritis have a family history of either psoriasis or psoriatic arthritis in a first-degree relative.
Genes on chromosome 6p have been associated with both psoriasis and psoriatic arthritis.
Other genes have been identified in genome wide scans.

Some infections may predispose to psoriasis and psoriatic arthritis
Trauma may precipitate psoriasis – it is know as the Koebner phenomenon, where psoriasis develops in a site of trauma. There are case reports and series of patients whose psoriatic arthritis was precipitated by trauma, but in most cases cause and effect cannot be absolutely confirmed.

There are a number of immunological abnormalities reported in both psoriasis and psoriatic arthritis.

Both B and T cells, cytokines and chemokines are important in both the development and perpetuation of inflammation in psoriatic arthritis.
Tumour necrosis factor has been found to be elevated in blood and tissue samples.
This cytokine is important in trigerring other cytokines and chemokines which are important in the development of inflammation and tissue damage in psoriatic arthritis.
Most investigators believe that there is an interplay between these factors, such that in the predisposed individual who comes into contact with the appropriate environmental factor there are immunological abnormalities which allow the disease to perpetuate.
It is not absolutely clear whether the same cause and mechanism are working in both the skin and the joint manifestations.