2227 Sporadic late-onset nemaline rod myopathy associated with monoclonal gammopathy

A 72-year-old man developed progressive camptocormia associated with head drop, dysphagia, proximal muscle weakness, numbness to the ankles, and 20kg weight loss over a 2 year period. Background history was significant for thyroid cancer treated with total thyroidectomy resulting in left accessory nerve injury, type 2 diabetes mellitus, hypertension, and gout. Examination revealed a man with reduced muscle bulk who walked with a flexed spine. He had weakness of neck flexion and proximal muscles with normal reflexes and reduced pin-prick sensation to both feet. Nerve conduction studies showed length-dependent axonal sensorimotor neuropathy. Concentric needle electromyography showed widespread reduced recruitment of small polyphasic units consistent with a myopathic process. Creatine kinase level was normal. Myositis panel demonstrated low positive Mi2 of uncertain significance. An initial deltoid muscle biopsy did not show evidence of myopathy. Due to worsening of symptoms, a repeat muscle biopsy of vastus lateralis was performed, revealing atrophic myofibres with a patchy granular appearance. Electron microscopy identified nemaline rods. An IgG kappa paraprotein was identified. HIV serology was negative. A diagnosis of sporadic late-onset nemaline myopathy (SLONM) associated with monoclonal gammopathy was made. He was commenced on IVIG and referred for haematological evaluation. SLONM is a rare acquired adult-onset progressive myopathy associated with monoclonal gammopathy and HIV infection. It may present with head drop or dysphagia and is characterised electrophysiologically by a combination of axonal neuropathy and proximal myopathy. First-line treatment with intravenous immunoglobulin and second-line treatment with haematological/immunological therapies may result in significant improvement.