Incidence of malignancies in biopsy-proven inflammatory myopathy

Background: Inflammatory myopathy (IM) as a manifestation of paraneoplastic syndrome has been well-documented. However, the prevalence of malignancies reported varies across the studies. There are very few studies reported from Asia, only one from India. Aim: The aim of this analysis was to study the prevalence of malignancy in biopsy-proven cases of IM in India and to study the difference between malignant and non-malignant groups. Materials and Methods: The study was a retrospective review of case records of patients with a biopsy-proven IM attending Tertiary Care University Hospital. Results: Of the total 86 patients with biopsy-proven IM, 22 patients were polymyositis, 63 patients had dermatomyositis (DM) and one was with an inclusion body myositis, not included for further analysis. Associated malignancy was diagnosed in 6 (7%) patients, and five of them were females. Diagnosis of associated malignancy was identified at the time of diagnosis of IM in four (66.7%) patients. All the six patients with an associated malignancy had DM. Only one patient died within 1 year of diagnosis. Creatinine kinase was much lower in patients with malignancy associated IM than in patients with no malignancy (P < 0.0001). Conclusion: The prevalence of malignancy was very low in our cohort as compared to the studies from other countries. Breast cancer was the most common malignancy associated with DM. The type of associated malignancy was quite variable.