An unusual myopathy with dual pathology: Case report

Abstract

Immune-mediated necrotising myopathy (IMNM) and inclusion body myositis (IBM) belong to a spectrum of conditions called the idiopathic inflammatory myopathies. However, they both represent distinct conditions, which differ in their clinical presentation, immuno-pathogenesis and in the available treatment options. In this poster presentation, I report the case of a 69-year old gentleman who had presented with a gradually progressive, symmetric, proximal myopathy with preservation of distal muscle strength including the deep finger flexors. There was no rash, bulbar disturbance or other focal neurological deficits. A serum creatine kinase was significantly elevated (4935 IU/L) and serological testing revealed strongly positive anti-HMGCR antibodies. Although these clinical and biochemical features robustly support a diagnosis of IMNM, skeletal muscle biopsy showed evidence of dual pathology with histopathological features consistent with a combination of IMNM and IBM. Computed tomography (CT) of the chest, abdomen and pelvis showed no underlying occult malignancy. The patient subsequently demonstrated an excellent clinical and biochemical response to high dose oral corticosteroid treatment, with improved muscle strength and mobility, and was simultaneously commenced on azathioprine immunotherapy. This poster illustrates an unusual case of biopsy-proven dual IMNM and IBM pathology in skeletal muscle. Herein, I discuss valuable learning points derived from this case, including the importance of interpreting muscle biopsy-findings in the context of the relevant clinical and biochemical profile when making a diagnosis, and constructing treatment strategies, in the myopathic patient.