Table of Contents

Washington University Experience | MUSCLE | Nemaline rod myopathy | 6B8B (Case 6) EM042 - Copy

Occasionally in a muscle fiber the normal relationship between thin actin filaments and thick myosin filaments is well seen as in this case. (electron micrographs) ---- Not shown & Comment: This is a chronic myopathy with type I fiber predominance, irregular internal architecture, and mitochondrial pathology, MHC class I upregulation by muscle fibers, and rods on ultrastructure. The changes are consistent with a nemaline myopathy or SLONM with the combination of mitochondrial pathology, immune features and rods. Phalloidin shows ill-defined aggregates in scattered small and normal sized fibers. Phalloidin staining of probable aggregates in some small fibers is consistent with the nemaline rods seen on ultrastructure. Mitochondria form subsarcolemmal aggregates of mildly abnormal sizes and shapes. Most do not have the marked size and shape variation of mitochondria in typical mitochondrial myopathy, or abnormal cristae, "parking lots", and matrix aggregates. Ring fibers were numerous and well formed.

---