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This article reports two cases of childhood-onset nemaline myopathy diagnosed by muscle pathology and genetic diagnosis. The two patients had onset in early childhood, with muscle weakness as the first manifestation, as well as long disease duration and slow progression. Gomori staining and hematoxylin-eosin staining showed red-stained rods in the sarcoplasmic cytoplasm and sarcolemma under a light microscope. Electron microscopy showed that the dense nemaline rods were located under the muscle fiber sarcolemma and parallel to the long axis of the muscle fibers, and some muscle fiber myofilaments were dissolved and necrotic. Gene testing found that one of the two patients had heterozygous mutation (c.1013A>C) in the ACTA1 gene, and the other had compound heterozygous mutation (c.18676C>T and c.9812C>A) in the NEB gene. The two mutations were more common in nemaline myopathy. Nemaline myopathy is a recessive or dominant inheritance myopathy, in which the nemaline rod in the cytoplasm of myocytes is a characteristic muscle pathological change. Pathological and genetic diagnosis is the gold standard for diagnosis of nemaline myopathy.

The morphological, immunohistochemical, and immunopathological analyses of muscle biopsy are essential for the diagnosis of idiopathic inflammatory myopathies (IIMs). However, they are also one of the most common causes of misdiagnosis. Although several diagnostic criteria have been proposed for the diagnosis of IIMs, misdiagnosis still remains common in clinical practice. The present study aims to characterize the inflammatory profile of IIMs, including the expression of MHC-I, MHC-II, MAC and infiltrating cells. We also investigated the sensitivity and specificity of MHC-I and MHC-II immunostaining for the diagnosis of IIMs. We found that the expression of MHC-I and MHC-II was both higher in IIMs than in non-inflammatory myopathies (NIMs). The distribution of MHC-I in IIMs is different from that of MHC-II. MHC-I is mainly located in the sarcoplasms, while MHC-II is located mostly on the sarcolemmas. Moreover, our findings suggest that MAC may be a potential marker to diagnose DM, and the combination of MHC-I and MHC-II immunostaining results in a higher sensitivity and specificity for IIM diagnosis, especially for DM. In addition, infiltrating cells in PM were mainly CD8+ cells, but we found in DM and NIMs they were primarily CD4+ cells, which is consistent with previous studies. Lastly, glucocorticoid treatment and disease duration have little effect on the MHC-I and MHC-II expression pattern. Our findings indicate that the immunostaining of inflammatory markers such as MHC-I, MHC-II, CD4, CD8, CD303 and MAC are of diagnostic value for IIMs regardless of the immunosuppression regime and disease duration., Competing Interests: None., (IJCEP Copyright © 2018.)