DRUG-THERAPY OF THE IDIOPATHIC INFLAMMATORY MYOPATHIES - PREDICTORS OF RESPONSE TO PREDNISONE, AZATHIOPRINE, AND METHOTREXATE AND A COMPARISON OF THEIR EFFICACY

PURPOSE: To identify factors associated with responses to treatment wi th prednisone, methotrexate, or azathioprine in patients with idiopath ic inflammatory myopathy, and to compare the efficacy of these drugs. PATIENTS AND METHODS: Data were collected on 113 adult patients meetin g criteria for definite idiopathic inflammatory myopathy in this retro spective cohort study. Patients were categorized as responding complet ely, partially, or not at all to each therapeutic trial based upon cli nical and laboratory criteria. RESULTS: Clinical group, presence of ce rtain myositis-specific autoantibodies, and time from disease onset to diagnosis influenced rates of complete clinical response to these the rapeutic agents. Patients with inclusion body myositis responded compa ratively poorly to prednisone the other drugs: 43% had no clinical res ponse to prednisone and none responded completely to any medication. P atients with autoantibodies to aminoacyl-tRNA synthetases or to signal recognition particle proteins were likely to respond partially, but n ot completely, to prednisone. No patient with a long delay to diagnosi s (greater than 18 months) responded completely, compared with 34% of those with a short delay (less than 3 months). A patient's response to the first course of prednisone predicted subsequent responses to pred nisone and to azathioprine better than response to methotrexate. Men r esponded to methotrexate better than women. Among certain subgroups of patients, responses to methotrexate were better than to either azathi oprine or retreatment with prednisone. CONCLUSION: Determining the cli nical group, autoantibody status, and time from disease onset to diagn osis of patients with myositis provides useful information in predicti ng clinical responses to therapy, and these factors should be consider ed in designing future therapeutic trials. Methotrexate therapy may be superior to either azathioprine or further steroid treatment alone in certain patients who do not respond completely to an initial adequate course of prednisone.