Sporadic late onset nemaline myopathy responsive to plasma exchanges discovered during a Graft-versus-host disease

Abstract

Sporadic late-onset nemaline myopathy (SLONM) is a rare adult-onset acquired myopathy characterized by the presence of clusters of nemaline bodies (rods) inside atrophic muscle fibers, with mild to no inflammation. Graft-versus-host disease (GVHD) is a systemic disorder occurring after allogenic hematopoietic stem cell transplant (allo-HSCT) variably associated with immune-mediated neuromuscular complications such as myositis, peripheral neuropathy, and myasthenic syndromes. A 49-year-old woman with an acute myeloid leukemia with translocation (6;9), and transcript DEK-NUP, was treated with chemotherapy and allo-HSCT. One month later, she developed a skin and digestive GVHD followed by the development of subacute progressive proximal muscular weakness. Serum CK were normal, and there was no MGUS. Muscle MRI showed oedema of paravertebral, pelvic girdle, and lower limbs muscle. Corticosteroids, IVIg, immunosuppressive, and anti-JAK treatments ameliorated the GVHD, but were ineffective on muscle weakness. A vastus lateralis muscle biopsy revealed clusters of rods in the majority of fibers and mild MHC-I expression in keeping with a SLONM. Plasma exchange therapy (PLEX) led to complete recovery of the muscle strength in several months. In conclusion we report a case of SLONM discovered during a chronic GVHD that responded to prolonged PLEX therapy.

Keywords: Graft-versus-host disease (GVHD); Plasma exchanges (PLEX); Sporadic late-onset nemaline myopathy (SLONM).