Microscopic Description -- New Onset Weakness


Cryostat sections from a deltoid muscle biopsy stained with H & E reveal a mild variation in fiber size, occasional internalized nuclei, and scattered eosinophilic cytoplasmic inclusions. Gomori trichrome reveals that the inclusions are dark, ovoid structures often occurring in circular arrays. Within these arrays or in isolation, areas of decreased staining are noted. The NADH-TR reaction (example 1 and example 2) reveals a severe, moth-eaten or multi-core appearance to the intermyofibrillar network. The cytoplasmic inclusions do not react with NADH-TR. However, they are strongly reactive with immunohistochemical stains for actin. A longitudinal section shows the multi-cores oriented perpendicular to the long axis of the myofibers. Regions of absent staining are seen with the myosin-ATPase reaction (pH 9.4) (example 1 and example 2).

Electron microscopy: The cytoplasmic inclusions are seen as ovoid, electron dense structures surrounded by clearer halos and an outer rim of disorganized fibrils. These cytoid bodies (cb) are associated with cores -- the regions of myofilament disorganization and degeneration with Z-band streaming that lack mitochondria (and therefore do not stain with NADH-TR or Gomori trichrome), glycogen, and sarcotubular elements.



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