Vacuolar myopathy associated with lambda light chain myeloma: a case report and review of the literature

Vacuolar myopathy is a muscle disease characterized by inefficient autophagy and the accumulation of intracytoplasmic degradation products in autophagic vacuoles. Acquired vacuolar myopathy associated with monoclonal gammopathy is a novel clinical entity first described in 2019. The objective of the present article is to describe the first case of an acquired vacuolar myopathy associated with lambda light chain myeloma.

A 52-year-old man was admitted to our nephrology department for acute kidney injury and was diagnosed with lambda light chain multiple myeloma. The patient presented with supraventricular arrythmia and developed rapidly progressing muscle weakness of the face and all four limbs, with a myogenic electromyographic pattern. A muscle biopsy highlighted muscle fibre vacuoles and lambda light chain deposits. Cardiac magnetic resonance imaging revealed concentric hypertrophy and subepicardial areas of fibrosis that were suggestive of an infiltrative disease. There were no signs of amyloidosis. Treatment with a combination of bortezomib, lenalidomide and dexamethasone gave a good hematologic response, and the patient recovered near-normal levels of muscle strength in the following six months. The number of episodes of arrythmia decreased.

Clinicians should be aware that lambda light chain myeloma may cause lambda light-chain deposits within muscle fibres and vacuolar myopathy. A corticosteroid-sparing strategy for vacuolar myopathy does not appear to be necessary when the course of the myeloma is favourable. Myopathy associated with monoclonal gammopathy is an emerging entity. Given that monoclonal gammopathy is very common in older adults, the appearance of muscle impairments in this context could prompt the physician to consider the initiation of corticosteroids, immunosuppressive agents, or intravenous immunoglobulins. Electromyography and muscle biopsy results can guide the diagnosis.