Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy of the peripheral joints and axial skeleton, occurring in 7–42% of patients with psoriasis, which affects 1– 3% of the general population.
Recent community-based epidemiological studies have suggested an incidence rate of approximately 6/100,000 per annum and a prevalence of 1/1000. The male:female ratio is 1:1, and the peak incidence occurred at 45-54 years of age.
Comparison between Psoriatic Arthritis and Rheumatoid Arthritis
|DIP joint involvement||++||-|
|Symmetric joint involvement||+/-||++|
|Erythema over affected joint||++||-|
(-) not seen; (+/-) uncommon; (+) common; (++) very common
Adapted from Gladman D. Psoriatic Arthritis. Oxford Textbook of Rheumatology. 3rd ed.; 2004
Treatment of Psoriatic Arthritis with Biologic Agents
|TNF-a Inhibition||Infliximab: chimeric (75% human, 25% mouse) mAb targeting TNFa, improves both synovitis and skin disease. It is administered as an intravenous infusion in conjunction with oral MTX, initially at weeks 0, 2, 6, and every 4-8 weeks thereafter.|
|Etanercept: human p75 TNF receptor/IgG1 fusion protein neutralizes both TNFa and TNFß (lymphotoxin). Improves both skin psoriasis and PsA.|
|Adalimumab: Humanized mAb targeting TNFa. It is administered as a sc injection every week or every other week.|
|Costimulation Inhibition||Alefacept: is a human LFA-3/IgG1 fusion protein, which binds to the CD2 receptor on T cells, thereby selectively depleting CD45RO+ memory-effector T-cells, approved for severe skin disease, worked for PsA in a small open trial and currently undergoing RCT.|
|Efalizumab: humanized mAb disrupts the T cell costimulatory LFA-1-ICAM-1 interaction. It is approved for severe skin psoriasis and is currently undergoing trials for PsA indication.|
The prognosis for patients with PsA generally varies according to the anatomic pattern: