Amyloid Myoneuropathy Mimicking Inclusion Body Myositis

Inclusion body myositis (IBM) is a slowly progressive myopathy affecting proximal and distal musculature with typical onset of symptoms after age 50 years.Inclusion body myositis more often affects males and results in a classical pattern of early asymmetric weakness and wasting of forearm flexors (wrist and long finger flexors), quadriceps and ankle dorsiflexors.Inclusion body myositis is more frequently associated with a monoclonal gammopathy than is seen in the general population but the implications of this association remain unclear 1 .Importantly, there is no available therapy to slow disease progression in IBM.Primary systemic amyloidosis (AL) typically results in light chain deposition in the tongue, kidneys, heart, liver, spleen and peripheral nerves with accompanying respective clinical sequelae.Rarely, light chain deposition can focally involve components of the nervous system.Peripheral nerve complications include carpal tunnel syndrome, dysautonomia and polyneuropathy 2,3 .Amyloid myopathy is rare and typically demonstrates proximal muscle involvement and electrophysiological findings indistinguishable from the inflammatory myopathies 4 .Prompt differentiation of amyloid myopathy from the inflammatory myopathies is essential as AL may respond to chemotherapy resulting in improved progression free survival 5 .We report a case of AL presenting with predominant myopathy clinically suggestive of IBM and with similar findings on initial muscle biopsy, an important distinction in light of recent treatment advances in AL. CASE REPORTA 59-year-old right-handed man was referred to the Calgary Neuromuscular Clinic for progressive weakness over five years.He described left knee "give-way" while skiing as his initial complaint.Over time, he noticed increasing difficulty to keep up with others while walking.Ascending stairs became more challenging and his legs would give away intermittently.He denied symptoms of foot drop or proximal limb weakness.Gradually he noticed progressive bilateral hand grip weakness associated with dropping of items.He was still able to button up clothing and use a zipper.Over the past year he observed that his ability to reach up with his hands became more difficult and that food would stick in his throat without choking.Since the onset of weakness the patient described shortness of breath on exertion, and more recently, orthopnea but no morning headache.The patient did not have any cognitive complaints, rash, sensory symptoms, pain, diplopia or ptosis.His past medical history and family history were non-contributing to his final diagnosis.On examination cardiac, abdominal and respiratory examinations were normal.Mental status, language testing and

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