Psoriatic arthritis

1. (1) Epidemiologic, clinical, radiologic and serologic evidence suggests that psoriatic arthritis is a specific entity and not the coincidental occurrence of two common diseases, psoriasis and rheumatoid arthritis. 2. (2) Psoriatic arthritis may be defined as psoriasis associated with inflammatory arthritis (peripheral arthritis and/or spondylitis) and usually a negative serologie test for rheumatoid factor. 3. (3) Epidemiologic evidence for psoriatic arthritis is based on the finding of a significantly higher prevalence of psoriasis in arthritic populations and, conversely, a significantly higher prevalence of arthritis in psoriatic populations compared with controls. 4. (4) Clinical characteristics of the disease include: almost equal distribution between males and females; peripheral arthritis involving few small joints in asymmetrical fashion; involvement of DIP joints; sausage digits; arthritis mutilans; ankylosing spondylitis; gout-like onset; higher incidence of nail involvement than occurs in uncomplicated psoriasis. The rash may present with arthritis, or, equally, may precede or succeed joint involvement. 5. (5) Radiologic characteristics of the disease include: erosion of terminal phalangeal tufts (acro-osteolysis); whittling of phalanges, metacarpals, and metatarsals; cupping of proximal ends of phalanges, metacarpals, and metatarsals; ankylosis of IP and MP joints; lack of symmetry; severe destruction of isolated small joints: predilection for DIP and PIP joints with relative sparing of MP joints; sacro-iliitis or ankylosing spondylitis. 6. (6) Laboratory characteristics are: negative serologic tests for rheumatoid factor; hyperuricemia; various changes of doubtful specificity in blood proteins and enzymes. 7. (7) Morbid anatomical findings include excessive fibrous tissue in affected joints and abnormal nailfold capillaries in both normal and psoriatic skin. 8. (8) Family studies have shown that psoriatic arthritis is probably determined genetically in a multifactorial manner. Environmental factors such as trauma may be important in triggering arthritis in the genetically predisposed. 9. (9) Familial and clinical interrelationships exist between psoriatic arthritis and other seronegative arthritides, particularly Reiter's disease, idiopathic ankylosing spondylitis, and the intestinal arthritides. 10. (10) Treatment of psoriatic arthritis is the same as the routine treatment of the individual components of the disease (psoriasis, peripheral arthritis, and spondylitis). However, antimalarials should be avoided as they exacerbate the rash. Folate antagonists (e.g., methotrexate) may be tried in severe cases not responding to traditional and less potentially harmful treatment. 11. (11) With regard to pain and disability, the prognosis in psoriatic arthritis is better than in rheumatoid arthritis.