The expression of C5b-9, HLA-1 and p62 in inflammatory myopathies diagnosed locally

Abstract

Inflammatory myopathies are a group of muscle diseases characterized by chronic muscle inflammation and weakness. There are five main types of inflammatory myopathies which include; dermatomyositis, polymyositis, inclusion body myositis, antisynthetase syndrome and immune-mediated necrotizing myopathy. The diagnostic workup generally includes a muscle biopsy which helps to assess the morphological features of the muscle. Inflammatory myopathies have many overlapping morphological characteristics, however, there are some unique features for each subset, which can be assessed by immunohistochemistry. Three immunomarkers; Human Leukocyte Antigen-1 (HLA-1), p62 and C5b-9 (membrane attack complex, MAC) are recommended as part of the muscle biopsy workup when inflammatory myopathy is suspected. In this study, an optimised IHC protocol for the novel C5b-9 antibody and the new antibody clone for HLA-1 immunostaining on fresh frozen muscle tissue was established. The samples consisted of frozen muscle biopsies which were retrieved from the Immunohistochemistry laboratory (Pathology Department at Mater Dei Hospital), where fresh frozen tissue is stored at -80°C. Immunostaining of C5b-9, HLA-1 and p62 was done on 50 previously diagnosed cases consisting of 25 inflammatory and 25 non-inflammatory myopathies. C5b-9 was positive in 21 (84%) inflammatory cases and 7 (28%) non-inflammatory cases. HLA-1 was overexpressed in all the inflammatory cases and in 10 (40%) non-inflammatory cases while p62 staining was detected in 20 (80%) inflammatory cases and in 11 (44%) non-inflammatory cases. The sensitivity for the diagnosis of inflammatory myopathies of C5b-9, HLA-1 and p62 were 84%, 100% and 80% respectively. A specificity of 72% was obtained for C5b-9, 60% for HLA-1 and 48% for p62. The optimisation and implementation of the novel C5b-9 immunostain for fresh frozen muscle biopsies will aid in the diagnostic accuracy of inflammatory myopathies. Moreover, positive control muscle tissue was established to be routinely used in the workup of inflammatory myopathies. This will ensure optimal quality, reproducible staining results for C5b-9, HLA-1 and p62 that can serve as a complementary diagnostic tool for the diagnosis of inflammatory myopathies and other rare neuromuscular disorders.