Chemotherapy-based approach is the preferred treatment for sporadic late-onset nemaline myopathy with a monoclonal protein.

Sporadic late-onset nemaline myopathy (SLONM) associated with monoclonal protein (MP) is a rare disease with an aggressive, and often fatal course. Whether SLONM + MP represents a malignancy or dysimmune disease remains unclear. Currently, two main approaches are used to treat SLONM + MP: nonchemotherapy-based treatment (immunosuppression, intravenous immunoglobulins, plasmapheresis and plasma exchange) or chemotherapy with or without autologous stem cell transplantation. Due to the rare occurrence of the disease, the best treatment modality is unknown. We analyzed treatment and outcomes in a large cohort of 53 patients with SLONM + MP: four our own patients and 49 cases from published literature. Neurological improvement in the nonchemotherapy group (N = 25) was observed in 52% of patients: 8% reached marked improvement, 8% moderate response, 36% mild response; none reached complete remission (CR). In the chemotherapy group (N = 28), neurological improvement was seen in 86% of patients: 46% reached CR, 25% marked response, 11% moderate response and 4% mild response. The best neurological improvement correlated with deep hematological remission. Mean time to best response in the chemotherapy group was 8 months versus 21 months in the nonchemotherapy group (P < .001). Overall survival was higher in patients in the chemotherapy group. A chemotherapy approach should be the preferred treatment for patients with SLOMN + MP with the goal to reach complete hematologic remission. Based on the clinical, morphological peculiarities, aggressive disease course and superior clinical benefits of chemotherapy over nonchemotherapy, SLONM + MP should be considered as a hematological malignancy with the presence of MP of clinical rather than undetermined significance.