Bortezomib-Induced Myopathy in Multiple Myeloma: A Case Report

Bortezomib is a widely used proteasome inhibitor for multiple myeloma, and its neurotoxicity, particularly peripheral neuropathy, is well recognized.By contrast, bortezomib-induced myopathy has rarely been reported and remains underrecognized in clinical practice.We describe a biopsy-supported case of bortezomib-induced myopathy in a patient with multiple myeloma who presented with progressive proximal lower-extremity weakness.A 68-year-old woman with multiple myeloma developed progressive bilateral proximal lower-extremity weakness approximately 6 weeks after starting bortezomib-based chemotherapy.Neurologic examination showed predominant proximal weakness, preserved distal strength, and no sensory deficits.Needle electromyography demonstrated myopathic motor unit potentials with early recruitment and no abnormal spontaneous activity.Serum creatine kinase levels were within the normal range.Biopsy of the left vastus medialis showed myofiber size variability, degenerating myofibers with lipid-laden microvacuoles, and moderate atrophy involving both type 1 and type 2 fibers, without selective type 2 fiber atrophy; these findings were consistent with bortezomib-induced myopathy.After bortezomib was discontinued, the patient showed gradual clinical and electrophysiologic improvement.This biopsy-supported case underscores the need to consider bortezomib-induced myopathy in patients with multiple myeloma who develop unexplained proximal muscle weakness.Early recognition is important because withdrawal of the offending agent may allow functional recovery.