Amyloidosis is one of the known systemic diseases that can cause a variety of neurological symptoms. Amyloid myopathy (AM) is a rare presentation of systemic amyloidosis (AL) or isolated AM. AM can have features that mimic a variety of inflammatory myopathies. MRI of the involved muscle group, echocardiogram, and comprehensive myositis panel can all be helpful, but gold standard for diagnosis is muscle biopsy with Congo red staining. 

A 56 year-old woman with past medical history of diabetes, hypothyroidism, and hypertension, presented with one year of progressive lower extremity weakness. Patient was instructed to go the emergency department by her PM&R physician due to multiple falls in the setting of lower extremity weakness. Exam showed mild proximal bilateral arm weakness and severe proximal lower extremity weakness. Labs showed elevated TSH (33), low T4 (undetectable range), elevated ESR (greater than 130), and elevated CK (1152). MRI thighs showed diffuse muscle edema in bilateral thighs and hips with associated fatty atrophy. Myomarker panel and ANA were unremarkable. Patient's weakness persisted six months later despite thyroid hormone supplementation. NCS/EMG were done, which showed severe myopathy with spontaneous activity, consistent with an inflammatory myopathy. Serum/urine electrophoresis revealed monoclonal IgG lambda. Bone marrow biopsy revealed diagnosis of multiple myeloma. Patient was started on chemotherapy regimen and had muscle biopsy of her right biceps, which revealed apple green birefringence under polarized light, consistent with amyloidosis. Echocardiogram was negative for cardiac amyloid involvement.