Skeletal Myopathy as the Initial Manifestation of Light Chain Multiple Myeloma.

Monoclonal gammopathies due to plasma cell dyscrasias can cause various rare neuromuscular disorders. The peripheral nervous system is most commonly affected, while muscle diseases associated with monoclonal gammopathies are rare. Skeletal myopathy, as a manifestation in the context of multiple myeloma, is extremely uncommon and is usually the result of immunoglobulin light chain (AL) amyloidosis deposits in the muscles. Here we present an atypical case of a patient with generalized myopathy as the presenting manifestation of light chain multiple myeloma. Interestingly, muscle involvement in our case was not the consequence of AL amyloidosis deposits but rather due to non-amyloid light chain deposition disease associated with light chain multiple myeloma. LEARNING POINTS: Light chain multiple myeloma can present as myopathy.Creatine kinase and muscle biopsy specimens only examined using routine stains can be normal in this condition. © EFIM 2020.