D. Sporadic late-onset nemaline rod myopathy
Electron microscopy of the vastus lateralis muscle biopsy identified nemaline rods within several muscle fibers (Figure 2). A diagnosis was made of sporadic late-onset nemaline rod myopathy (SLONM) associated with monoclonal gammopathy. The patient received a 6-month trial of intravenous immunoglobulin without clinical improvement. He has subsequently been referred for hematological evaluation and potential autologous hematopoietic stem cell transplant.
SLONM is a rare, acquired, adult-onset progressive myopathy first described by A. G. Engel in 1966.1 The typical clinical phenotype is characterized by weakness and atrophy of predominantly proximal and axial muscles, which may lead to camptocormia or head drop. Dysphagia and dyspnea are common, occurring in approximately 50% of cases,2 with respiratory failure a common cause of death.3 Cardiac involvement is reported, manifesting as conduction abnormalities and/or cardiomyopathy.2,4