Reader Response: Clinical Subgroups and Factors Associated With Progression in Patients With Inclusion Body Myositis

We read with interest the article by Michelle et al.¹ about clinical subgroups and factors associated with progression in patients with inclusion body myositis (IBM). The authors used Griggs criteria,² European Neuromuscular Centre 2011 criteria, and Lloyd Greenberg data-derived criteria,³ including endomysial inflammation, invasion of non-necrotic fibers, and rimmed vacuoles.

This triad was only seen in 43% of biopsies and rimmed vacuoles were present in only 66%, which are low percentages. The authors argued that incomplete histopathologic patterns—apart from clinical misdiagnosis—may be a reason for misclassification as polymyositis (PM). They proposed less invasive diagnostic criteria and putting more value on clinical examination, such as quadriceps and finger-flexor weakness.

It has been shown that a diagnosis of PM has to be re-evaluated with modern approaches⁴ and that many of the PM-mito cases are actually patients with early IBM, which cannot be identified on clinical grounds only because many patients have, in fact, mild nonspecific clinical signs.⁵

We recommend more precise and complete diagnostic procedures,⁴ including major histocompatibility complex class I and II, p62, TAR DNA-binding protein 43, complement patterns, T-cell characterization,⁶ and mitochondrial abnormalities,⁷ to determine whether a biopsy specimen corresponds to IBM.