NEW YORK – Unexpectedly and conflicting with previous reports, a careful analysis of a relatively large series of patients with psoriatic arthritis mutilans found that most had axial involvement.
In a series of 56 patients with psoriatic arthritis (PsA) mutilans drawn from 610 consecutive patients with PsA, 65% had evidence of axial disease on the most recent radiograph. Of these, 57% had radiographic sacroiliitis, which was bilateral in 80%.
"This proportion far exceeds the typical 25% incidence of axial disease reported in the literature," according to Dr. Deepak Jadon, a specialist registrar in rheumatology at the Royal National Hospital for Rheumatic Diseases, Bath, England.
Dr. Deepak Jadon
The proportion of confirmed PsA mutilans cases, at 9%, was also higher than the 5% typically reported, according to Dr. Jadon, who presented these findings at the joint meetings of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and the Spondyloarthritis Research & Treatment Network (SPARTAN). Referral to a specialty clinic may explain the higher rate, but PsA mutilans could only be ruled out, because of inadequate radiographs, in 483 of the 610 patients, so the actual proportion could be even higher.
In 35 of the patients with PsA mutilans, defined as osteolysis involving at least 50% of the visualized articular surface on both sides of the joints, serial radiographs confirmed that this disease is progressive. In this series, 37% of the patients had PsA mutilans at the time of the first radiograph, but the rest developed PsA mutilans over the course of follow-up.
Of this second group, 84% had received a disease-modifying antirheumatic drug (DMARD) prior to developing PsA mutilans, an observation that "suggests DMARDs may not prevent the onset of this condition," Dr. Jadon reported, cautioning that there are other potential explanations.
Using a random-effects model, "different patterns of progression were observed in the feet and hands," Dr. Jadon reported. In both groups, the most common pattern was an initial surge of activity followed by a tapering of rate of progression. However, a second surge of activity in the hands was not observed in the feet.
When compared to unaffected PsA patients, those with PsA mutilans were on average younger (33 vs. 40 years; P = .039) and more likely to have nail dystrophy (83% vs. 45%; P = .0002). The severity of nail dystrophy appeared to correlate with the severity of joint involvement.
The most commonly affected joints in this series were the metatarsophalangeal joint of the big toe, the proximal interphalangeal joint of the thumb, and the metacarpophalangeal joint of the index finger. While many patients had monoarticular involvement at the time of diagnosis, 80% of patients in this series had polyarticular disease on the most recent radiograph.
Not surprisingly, functional limitations were significantly greater for patients with PsA mutilans on standardized health assessment questionnaire (HAQ) when compared with patients with PsA (P = .048). The differences involved functions affecting both the hands, such as those relevant to grip strength, and the feet.
Data from this series did not provide any insight on treatment efficacy. Biologic use in those with serial radiographs, which included a sizeable number of patients managed before the biologic era, was too infrequent to infer effect on disease progression. However, the frequent exposure to DMARDs in patients with documented progression suggests benefits may be limited.
Dr. Jadon suggested that prospective data for PsA mutilans, which is widely regarded as the least common but most severe form of PsA, are now needed to determine which treatments have the greatest potential to improve long-term outcome.
Dr. Jadon reported no potential conflicts of interest.