Corticosteroid Monotherapy Is Usually Insufficient Treatment for Idiopathic Inflammatory Myopathy

Idiopathic inflammatory myopathies (IIM) are a rare group of autoimmune diseases characterized by muscle inflammation. High-dose corticosteroids are conventionally used as the first-line therapy for IIM, but early introduction of noncorticosteroid immunosuppressive agents has become increasingly common in recent years despite a paucity of compelling evidence to support this. Here, we systematically analyze therapeutic practice patterns of IIM in a large municipal safety net medical center. We conducted a retrospective chart review of all adult patients attending rheumatology clinics at the Cook County Health and Hospital Systems from 2006 to 2011 with a diagnosis of IIM. Data collected included patient demographics, diagnosis, immunosuppressive therapies, serial serum creatine kinase (CK) measurements, and serial muscle strength testing. One hundred eight patients fulfilled eligibility criteria. The mean duration of follow-up was 62 months (range, 1-351 months). At presentation, the mean strength in the weakest muscle group was rated as 3.6 out of 5 (range, 1-5; SD 0.9), the mean initial CK was 4720 U/L (range, 23-38, 461; SD 6, 795), and initial mean prednisone dosage was 48 mg/d (range, 0-100, SD 22). At the end of the follow-up period, mean strength in the weakest muscle group was 4.6 out of 5 (range, 2-5; SD 0.7), mean peak CK was 412 (24-7533; SD 875), and the mean prednisone dosage was 12.7 mg (0-80; SD 17.5). Only 15 patients (14%) received exclusively corticosteroid monotherapy during the follow-up period. Ninety-three patients (86%) received additional immunosuppressive agents. Over the course of their illness, only a minority of patients in our cohort of IIM patients was treated with corticosteroids alone. It is unlikely we will determine optimal therapy in the absence of a large controlled study comparing corticosteroids versus a combination regimen, but it seems that rheumatologists favor addition of second-line immunosuppressive agents.