The minimal disease activity criteria used to identify low disease activity in psoriatic arthritis (PsA) may not be useful as a treatment target in patients with extended skin involvement, according to the results of a small study.

Minimal disease activity (MDA) for PsA is a composite measure encompassing clinically important aspects of the disease: arthritis, psoriasis, enthesitis, pain, patient-assessed global disease activity, and physical function and provides an objective target for therapy in clinical trials, Dr. Josefina Marin of the Hospital Italiano de Buenos Aires and her associates wrote in the Journal of Rheumatology.

To evaluate components of the MDA criteria, the research team enrolled 83 consecutive patients with PsA aged over 18 years who were attending their clinic. Patients needed to fulfill five out of the seven criteria to be classified as having MDA.

An assessment by a single experienced rheumatologist revealed that 41 patients met MDA criteria, with only 7.4% of these patients not satisfying the tender/swollen joint–count criteria.

However, only 51% (n = 21) of patients fulfilling MDA fulfilled the skin criteria (Psoriasis Area and Severity Index [PASI] and body surface area [BSA]), a percentage not statistically different from the 36% of patients not in MDA (n = 15; P = .154). “This is important because MDA may therefore not be useful as a treatment target in patients with extended skin involvement,” the investigators wrote (J Rheum. 2016 Mar 1. doi: 10.3899/jrheum.151101).

The investigators noted that the selection of the target was of crucial importance when implementing a treat-to-target and tight control strategy. “In this sense our study provides reassurance that almost all patients at MDA will have no swollen/tender joints but also raises some concerns that the skin might not be well controlled if the MDA is used as the only target to treat patients with both joint and skin involvement,” they wrote. One explanation could be that the cutoff values selected in the MDA criteria for skin involvement are too stringent for therapies currently available, they suggested.

MDA seems to be a valuable tool to define low disease activity in patients with PsA, but the skin component requires further evaluation, they concluded.

The research was partially supported by the PANLAR/Abbvie Rheumatology prize 2012.


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