Although psoriatic arthritis is not the only disease associated with dactylitis — other culprits are sarcoidosis, septic arthritis, tuberculosis, and gout — dactylitis is one of the characteristic symptoms of psoriatic arthritis. Dactylitis is seen in as many as 35% of patients with psoriatic disease. Dactylitis clinically presents — as in this patient — with sausage-like swelling of the digits. It is included in the Classification Criteria for Psoriatic Arthritis (CASPAR) as one of the hallmarks of psoriatic arthritis.
Dactylitis has been thought to be a result of the concomitant swelling and inflammation of the flexor tendon sheaths of the metacarpophalangeal, metatarsophalangeal, or interphalangeal joints. Flexor tenosynovitis can be detected by examination with MRI and ultrasound. Dactylitis is associated with radiologically evident erosive damage to the joints.
Patients with psoriatic arthritis are typically seronegative for rheumatoid factor and antinuclear antibody; antinuclear antibody titers in persons with psoriatic arthritis do not differ from those of age- and sex-matched controls. C-reactive protein may be elevated but is often normal. Lack of C-reactive protein elevation, however, does not mean that systemic inflammation is absent, but rather indicates that different markers are needed that allow better quantification of systemic inflammation in psoriasis and psoriatic arthritis.
Herbert S. Diamond, MD, Professor of Medicine (retired), Temple University School of Medicine, University of Pittsburgh; Chairman, Department of Medicine Emeritus, Western Pennsylvania Hospital, Pittsburgh, PA.
Herbert S. Diamond, MD, has disclosed no relevant financial relationships.