Sporadic late-onset nemaline myopathy with MGUS Long-term follow-up after melphalan and SCT

Objective: Sporadic late-onset nemaline myopathy (SLONM) is a rare, late-onset myopathy that progresses subacutely. If associated with a monoclonal gammopathy of unknown significance (MGUS), the outcome is unfavorable: the majority of these patients die within 1 to 5 years of respiratory failure. This study aims to qualitatively assess the long-term treatment effect of high-dose melphalan (HDM) followed by autologous stem cell transplantation (SCT) in a series of 8 patients with SLONM-MGUS. Methods: We performed a retrospective case series study (n=8) on the long-term (1-8 years) treatment effect of HDM followed by autologous SCT (HDM-SCT) on survival, muscle strength, and functional capacities. Results: Seven patients showed a lasting moderate-good clinical response, 2 of them after the second HDM-SCT. All of them had a complete, a very good partial, or a partial hematologic response. One patient showed no clinical or hematologic response and died. Conclusions: This case series shows the positive effect of HDM-SCT in this rare disorder. Factors that may portend an unfavorable outcome are a long disease course before the hematologic treatment and a poor hematologic response. Age at onset, level and type of M protein (kappa vs lambda), and severity of muscle weakness were not associated with a specific outcome. Classification of evidence: This study provides Class IV evidence that for patients with SLON-MMGUS, HDM-SCT increases the probability of survival and functional improvement.