Differential diagnosis
Several conditions can mimic the clinical presentation of psoriatic arthritis including rheumatoid arthritis, osteoarthritis, reactive arthritis, gouty arthritis, systemic lupus erythematosus, and inflammatory bowel disease-associated arthritis. In contrast to psoriatic arthritis, rheumatoid arthritis tends to affect the proximal joints (e.g., the metacarpophalangeal joints), involves a greater number of joints than psoriatic arthritis, and affect them symmetrically. Involvement of the spinal joints is more suggestive of psoriatic arthritis than rheumatoid arthritis. Osteoarthritis shares certain clinical features with psoriatic arthritis such as its tendency to affect multiple distal joints in an asymmetric pattern. Unlike psoriatic arthritis, osteoarthritis does not typically involve inflammation of the sacroiliac joint. Psoriatic arthritis sometimes affects only one joint and is sometimes confused for gout or pseudogout when this happens. Classification
There are five main types of psoriatic arthritis:
Oligoarticular: This type affects around 70% of patients and is generally mild. This type does not occur in the same joints on both sides of the body and usually only involves fewer than 3 joints. Polyarticular: This type accounts for around 25% of cases, and affects five or more joints on both sides of the body simultaneously. This type is most similar to rheumatoid arthritis and is disabling in around 50% of all cases. Arthritis mutilans (M07.1): Affects less than 5% of patients and is a severe, deforming and destructive arthritis. This condition can progress over months or years causing severe joint damage. Arthritis mutilans has also been called chronic absorptive arthritis, and may be seen in rheumatoid arthritis as well.
Epidemiology
Seventy percent of people who develop psoriatic arthritis first show signs of psoriasis on the skin, 15 percent develop skin psoriasis and arthritis at the same time, and 15 percent develop skin psoriasis following the onset of psoriatic arthritis.Psoriatic arthritis can develop in people who have any level severity of psoriatic skin disease, ranging from mild to very severe.Psoriatic arthritis tends to appear about 10 years after the first signs of psoriasis. For the majority of people, this is between the ages of 30 and 55, but the disease can also affect children. The onset of psoriatic arthritis symptoms before symptoms of skin psoriasis is more common in children than adults.More than 80% of patients with psoriatic arthritis will have psoriatic nail lesions characterized by nail pitting, separation of the nail from the underlying nail bed, ridging and cracking, or more extremely, loss of the nail itself (onycholysis).Enthesitis is observed in 30 to 50% of patients and most commonly involves the plantar fascia and Achilles’ tendon, but it may cause pain around the patella, iliac crest, epicondyles, and supraspinatus insertionsMen and women are equally affected by this condition. Like psoriasis, psoriatic arthritis is more common among Caucasians than African or Asian people. References
External links
Psoriatic Arthritis at Patient.info
Guidelines of care for the management of psoriasis and psoriatic arthritis—National Guideline Clearinghouse
US National Institute of Arthritis and Musculoskeletal and Skin Diseases