To evaluate autoantibody status in patients with dermatomyositis (DM) and its relationship to treatment response to intravenous immunoglobulin (IVIG).

DM is an immune-mediated inflammatory myopathy with two subsets of autoantibodies identified in patients: myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA). The randomized, placebo-controlled ProDERM study recently demonstrated the efficacy and safety of IVIG in DM patients.

This was a post-hoc analysis of the ProDERM study. DM patients received 2 g/kg IVIG (n=47) or placebo (n=48) every 4 weeks for 16 weeks, then eligible patients (N=91) received IVIG through Week 40. Patient serum samples were analysed at baseline for MSA and MAA. Treatment response was evaluated by Total Improvement Score (TIS) at Weeks 16 and 40 (minimal response ≥20; moderate/major ≥40).

At baseline, 49 (52%) patients were MSA-positive (MSA+), 13 (14%) were MAA-positive (MAA+), and in 33 (35%) no antibodies (Ab-ve) were detected. Ten patients were both MSA+ and MAA+. In MSA+ patients (IVIG + placebo arms), 71% (35/49) had at least minimal response at Week 16, vs 55% (18/33) Ab-ve patients (p= 0.12) and 38% (5/13) who were MAA+ (p=0.03). In MSA+ patients on IVIG, 83% showed TIS response at Week 16 vs 60% on placebo (p=0.07). For all patients, no significant difference between the three antibody groups was seen in percentage of patients with ‘moderate/major improvement’ at Weeks 16 or 40. Analysis of individual autoantibodies showed no significant difference in response rates of Ab+ vs Ab-ve patients at Weeks 16 or 40 for anti-synthetase antibodies nor for anti-Mi2 antibodies. However, significantly more anti-TIF positive patients had a minimal response at Weeks 16 (p=0.02) and 40 (p=0.03) vs those who were negative.