Sporadic late onset nemaline myopathy and immunoglobulin deposition disease

Abstract

In monoclonal gammopathy, organ dysfunction can occur due to deposition of immunoglobulin fragments. A rare form of acquired myopathy often associated with monoclonal gammopathy is sporadic late onset nemaline myopathy (SLONM), which is characterized by nemaline rods in myofibers. The pathogenetic link between monoclonal gammopathy and SLONM has not yet been elucidated. Case report of a patient with monoclonal gammopathy who developed a progressive myopathy, finally diagnosed as SLONM. A muscle biopsy showed mild myopathic changes. A second biopsy 1 year after clinical onset demonstrated deposition of immunoglobulin light and heavy chains and the presence of nemaline rods. The patient experienced marked improvement of muscle strength after autologous stem cell transplantation and treatment with bortezomib, a therapy that is known to be effective in light chain deposition disease. We speculate that deposition of light and heavy chains, rather than nemaline bodies, has myotoxic effects on skeletal muscle.