Sporadic late-onset nemaline myopathy with monoclonal gammopathy of undetermined significance: Report of four patients.

Sporadic late-onset nemaline myopathy (SLONM) is a rare, acquired muscle disease presenting with subacute progression in adulthood. It can be accompanied by a monoclonal gammopathy of undetermined significance (MGUS). We describe clinical and histopathological findings of four SLONM patients with MGUS. In all patients, nemaline rod, inter-myofibrillary network disruption, atrophic changes, peripheral basophilic discoloration, vacuole without rim, and cytoplasmic body without inflammation were seen. Three out of four patients were treated with prednisolone in combination with IVIG monthly and had an appropriate response to the treatment. The optimal first-line treatment remains unclear in SLONM-MGUS, although corticosteroids plus IVIg is associated with favorable clinical response. These treatment modalities might be used as an optional treatment before autologous stem cell transplantation; however, further studies with a higher number of patients are required.