Pitfalls in diagnostic myopathology of sporadic inclusion body myositis (SIBM).

ABSTRACT

Sporadic inclusion body myositis (SIBM) is the most common idiopathic inflammatory myopathy in Caucasians over the age of 50 years. The prevalence of SIBM in the Asian population was initially thought to be very low, although the recent study showed that the prevalence of SIBM in Japan is in fact similar to the prevalence in Australia and the USA. SIBM is a refractory myositis with associated myodegenerative features mimicking the neuropathology of Alzheimer’s disease. The diagnosis of definite SIBM requires the typical clinical features and the presence of an autoaggressive inflammatory reaction, rimmed vacuoles, and congophilic deposits or tubulofilamentous inclusions. About one-fourth of patients with the typical clinical features of SIBM did not fulfill the pathological criteria of the definite SIBM. These canonical biopsy features may be absent in the early stage of the disease. Here we review the typical findings and the diagnostic pitfalls of the muscle biopsy in SIBM.