Study of idiopathic inflammatory myopathies with special reference to borderland between idiopathic inflammatory myopathies and muscular dystrophies

Background: Idiopathic inflammatory myopathies (IIMs) form important treatable myopathies, hence it is important to recognize and categorize them. In some cases, the differential diagnosis between IIM and muscular dystrophies can be difficult. Aim: To study the clinical and laboratory features of patients with IIMs and compare and contrast this group with limb girdle muscular dystrophies (LGMDs). Setting and Design: A prospective study for the period of five years [1999-2004] was undertaken at a tertiary neuromuscular center. Materials and Methods: Bohan and Peter criteria were used for the diagnosis of IIM and Bushby criteria were used for the diagnosis of LGMD. Patients underwent history, clinical examination, hematological tests, electrophysiological studies and muscle biopsy. The biopsies were studied for histology and immunocytochemistry. A clinical scoring system was evolved to differentiate IIM from LGMD and was validated in a blinded manner. Receiver operator curves were used as the statistical method to analyze the sensitivity and specificity. Results and Conclusions: In the IIM group, dermatomyositis was most common, followed by polymyositis, occurring in young females. Overlap group was less common. In patients with polymyositis, onset in upper girdle was associated with adverse outcome. The scoring system helped to differentiate IIM from LGMD, mainly using clinical pointers. This was particularly valuable in chronic cases.