Two cases of sporadic late onset nemaline myopathy effectively treated with immunotherapy.

Sporadic late onset nemaline myopathy (SLONM) associated with monoclonal gammopathy of undetermined significance (MGUS) is an adult onset myopathy with poor clinical outcomes, requiring high-dose intravenous melphalan with autologous peripheral blood stem cell transplantation (HDM-SCT). Here we report two cases of SLONM associated with MGUS in which improvements were achieved only with immunotherapy. A 39-year-old woman had a two-year history of dropped head syndrome and progressive proximal weakness. On admission, she was able to walk with assistance and had lordosis with camptocormia. Combination therapy with plasmapheresis and intravenous immunoglobulin in addition to intravenous methylprednisolone pulse therapy ameliorated camptocormia and proximal weakness after one year. A 51-year-old man had difficulty in raising his arms and required walking assistance prior to visiting our hospital. He had proximal weakness and atrophy, winged scapulae, and gait disturbance. After combination immunotherapy, no progression was observed for 13 years. In both cases, patients did not desire to undergo HDM-SCT, and IgG kappa monoclonal protein was positive, of which the levels were normalized after immunotherapy. Combination immunotherapy can be a possible alternative to HDM-SCT in patients with SLONM. Both patients showed myogenic changes with abundant fibrillation, and needle EMG revealed positive sharp waves. Case 1 showed high signal intensities in MRI STIR/T2WI in muscles showing weakness. These findings are commonly observed in patients with myositis, suggesting that, without muscle biopsy, SLONM may be misdiagnosed as myositis. Muscle biopsy revealed scattered fibers with nemaline bodies without type 2B deficiency, which are important pathological findings that differentiate SLONM from congenital nemaline myopathy.