A rhesus macaque with generalized muscle atrophy and musculotendinous contractures was detected in our research center. Muscle biopsies showed myofibers with rimmed vacuoles and eosinophilic hyaline inclusions, accumulations of CD8+ and CD4+ lymphocytes and expression of major histocompatibility complex class I in myofibers. Intracellular inclusions were positive to Congo red. Semithin sections and transmission electron microscopy showed autophagic vacuoles within myofibers and myonuclei with inclusions of filaments. These morphological observations conform with the diagnostic criteria of human sporadic inclusion body myositis. This is the first report of this myopathy in nonhuman primates.
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