To study the electroclinical and histopathologic profile of idiopathic inflammatory myositis (IIM) with reference to prognosis and survival rate.
Materials and Methods:
Diagnosis of IIM was based on the Bohan and Peter criteria. Patients who improved and those whose condition worsened or who expired due to IIM per se at last follow-up were classified to have favorable and poor outcomes, respectively. Fisher’s exact test was used for univariate analysis of prognostic factors.
The study cohort consisted of consecutive 68 patients with IIM. The mean age at diagnosis was 36.5 years and females constituted 71%. Of these patients, 62% had definite IIM, 49% had polymyositis, 20% had dermatomyositis, and 29% had overlap syndrome. The mean follow-up period was 5.4 years. Prednisolone alone was used in 55 (80%), and azathioprine (1–3 mg/kg/day) alone in 12 (17.6%) as the initial treatment. Relapse of IIM with drug withdrawal was seen in 15 patients (22%); 70% had favorable outcome and 16% had expired. The treatment delay of ≤6 months (P = 0.001), absence of cardiac or lung involvement (P < 0.001), and positive biopsy (P = 0.033) were predictive of a favorable prognosis in the univariate analysis. In multivariate analysis, only the duration of illness of ≤6 months (P = 0.008) and the absence of cardiac or lung involvement (P = 0.001) predicted the favorable outcome at last follow-up. Cumulative survival rate was 95% at 1 year, 86% at the 5th year, and 80% at the 10th year.
Approximately, two-thirds of the patients showed good electroclinical and histopathologic correlations and an equal number improved with treatment. The treatment delay (≥6 months), presence of cardiac or pulmonary involvements, and negative muscle biopsy are bad prognostic factors.