Psoriatic arthritis. Arthroscope (endoscope) view of the inflamed lining, or synovium, of the knee joint in psoriatic arthritis. The synovium (synovial membrane) lines the fluid-filled capsule that encloses the joint. Psoriasis is a skin disease that occurs when new skin cells are produced around ten times faster than normal. It may also be associated with joint inflammation, as here. Although the underlying cause is not known, psoriasis often runs in families and can be brought on by stress, skin damage and illness. The arthritis may be treated with anti-inflammatory drugs, antirheumatic drugs or methotrexate to tackle the psoriasis.