PAM, the Evil "Twin" of PsA, May Resist DMARDs

Psoriatic arthritis mutilans (PAM) is the most severe and destructive form of psoriatic arthritis, but the common drugs that help PsA patients don’t seem to work well, according to a new study from the UK. 

The data suggest that antirheumatic disease modifying drugs (DMARDs) do not appear to prevent PAM or its disabling deformities, reports Deepak Jadon, MBBS, MRCP, a Specialist Registrar in rheumatology at the Royal National Hospital for Rheumatic Diseases in Bath, England.

PAM is characterized by osteolysis of the small joints of the hands and feet resulting in large joint erosion and shortening of fingers and toes forming thick bands of tissue that seriously restricts function, and subluxation (partial joint dislocation).  

In a retrospective study of 610 patients at the hospital’s PsA clinic, Jadon and colleagues set out to determine how PAM progresses and how quickly, analyzing clinical findings, lab tests, and radiographs taken at various intervals between 1974 and 2014.

Among the group, 8% (n=36) were found to have current X-ray features of PAM. There was no evidence of PAM in 483, but 91 had insufficient radiographs to determine whether mutilans was present.

Around half of the PAM patients (53%) were women, and they were younger than non-PAM cases when initially diagnosed with PsA (median age 33 vs age 40).

Almost 92% of the PAM patients were taking DMARDs (methotrexate, sulfasalazine, or leflunomide), compared to half of the patients without mutilans. Around a third of both groups were taking biologics.

“However, 87.5% of the PAM patients had initiated DMARDs before the first evidence of mutilans was seen on their X-rays,” Jadon says, which may suggest that DMARDs do not alter or prevent the onset of mutilans.  

Fewer than 38% had evidence of PAM on their earliest X-rays, but more than 80% displayed polyarticular mutilans on the most recent radiograph a median of 10 years later, “meaning more than 62% developed PAM despite DMARD treatment,” he says.

In an unexpected finding, 65% of the mutilans patients displayed evidence of axial disease on their most recent X-ray, a far greater percentage than the 25% previously reported in the literature, Jadon notes. More than half (57%) had radiographic sacroiliitis, the majority of which was bilateral and of high grade severity.

PAM patients had poorer function than the PsA patients, with significantly higher mean scores of 1.25 vs 0.63, indicating greater difficulty in activities, on the Health Assessment Questionnaire (HAQ). The difference was especially significant in hand grip strength. They also had a higher prevalence of nail dystrophy among compared to those with PsA (83% vs 45%), suggesting that nail disease is marker of progressing to more severe PsA.

Jadon was among eight international research fellows presenting at the first-ever joint meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and the Spondyloarthritis Research and Treatment Network (SPARTAN), held in New York City July 10-13^th.