Data from: Idiopathic inflammatory myopathy: inter-rater variability in muscle biopsy reading

Background: Despite its importance for diagnosing idiopathic inflammatory
myopathy (IIM) subgroups, muscle biopsy classification criteria have not
been standardized nor validated. Objective: We sought to determine
inter-rater variability in diagnosing individual muscle biopsy
abnormalities. Methods: We developed a scoring tool to analyze consensus
in muscle biopsy reading of an ad hoc workgroup of international experts.
Twenty-four samples from suspected IIM patients were randomly selected,
providing sections that were stained with standard histological and
immuno-histochemical methods. Sections were made available on an online
platform and experts were queried about myopathological features within
four pathological domains: muscle fibers, inflammation, connective tissue
and vasculature. A short clinical presentation of cases was included, and
experts were asked to give a tentative diagnosis of polymyositis,
dermatomyositis, inclusion-body myositis, anti-synthetase syndrome-related
myositis, immune-mediated necrotizing myopathy, non-specific myositis or
other disease. Fleiss’ Kappa values, scoring inter-rater variability,
showed the highest agreement within the muscle fiber and connective tissue
domains. Results: Despite overall low Kappa values, moderate agreement was
achieved for tentative diagnosis, supporting the idea of holistic muscle
biopsy interpretation rather than by adding up of individual features.
Conclusion: We conclude that assessment of individual pathological
features needs to be standardized and harmonized, and should be measured
for sensitivity and specificity for subgroup classification. Standardizing
the process of diagnostic muscle biopsy reading would allow identification
of more homogeneous patient cohorts for upcoming treatment trials.