An unusual presentation of inflammatory myopathy in a patient on natalizumab treatment for multiple sclerosis: A case report and review of myopathological classification of inflammatory myopathy

Acquired immune and inflammatory myopathies (IIMs) are traditionally subdivided into dermatomyositis, polymyositis, inclusion body myositis (IBM) and necrotizing autoimmune myopathy (NAM). Our patient is a 38-year old female who had history of Multiple Sclerosis and was on Natalizumab. Almost a year later, she presented with acute proximal bilateral upper extremity weakness with elevated CPK. She was initially labeled as having ‘viral myositis’. Her subsequent two admissions demonstrated worsening of muscle weakness with dysphagia which was initially unresponsive to high dose of steroids. She had an EMG which showed irritative myopathy and a muscle biopsy which showed IMPP. She eventually responded to pulse dose of steroids and IVIG and Natalizumab was held. The temporal relationship between the development of inflammatory myopathy in our patient and subsequent improvement in her course after discontinuation of the drug suggests that natalizumab may have played a role in our patient’s disease and warrants further investigation and vigilance. In addition to the case report, we hope to elaborate on the myopathological descriptions increasingly being used to describe the IIMs and to explore the potential link between natalizumab and the onset of IIM in our patient.