Idiopathic inflammatory myopathies (IIMs) are a group of heterogeneous diseases characterized by chronic muscle inflammation leading to muscle weakness and atrophy. While typically presenting with symmetrical muscle involvement, a subset of cases exhibits asymmetry, posing diagnostic challenges and implicating unique pathophysiological mechanisms. A recent study published in the Journal of Clinical Neuroscience highlights the frequency and characteristics of IIMs with asymmetric muscle involvement (IIMs-A) against classic IIMs (IIMs-C). This research, which spans a 12-year retrospective review conducted by Liu et al. (2019), represents an effort to deconstruct the enigmatic presentation of IIMs-A.
The research, focus of which centers on a cohort at the Qilu Hospital, reviewed data from 134 patients diagnosed with IIMs between April 2005 and August 2017. Distinctly, 13 (9.2%) of these patients were identified with IIMs-A. Among them, seven were diagnosed with dermatomyositis (DM), two with polymyositis (PM), and four with immune-mediated necrotizing myopathy (IMNM), as per the European Neuromuscular Centre (ENMC) criteria. The mean age of the group with IIMs-A was 59.1 years, with a duration from initial symptoms to examination of less than 12 months in 92.3% of the cases.
Significantly, the findings dove into clinical features, revealing a noteworthy aspect: 46.2% of IIMs-A patients dealt with weakness of distal limbs and bulbar symptoms, referencing the muscles responsible for speech, swallowing, and other cranial nerve-mediated functions. The impairment of finger flexion was observed in five patients (38.5%), yet intriguingly, no case showed finger flexion weaker than shoulder abduction. This distinct muscular pattern of involvement adds to the clinical heuristics for diagnosing such conditions.
Serological analysis unveiled that creatine kinase (CK) levels varied widely, ranging from 41 IU/L to 9125 IU/L with an average of 3192.7 ± 2769.9 IU/L. Moreover, serum positive anti-mitochondrial antibodies (AMAs) constituted an essential serological marker, as they were present in four patients (30.8%).
The examination then transected the biological layers down to histopathology; both endomysial fibrosis and inflammatory cell infiltration were prevalent in 92.3% and 84.6% of the patients, respectively. In a critical finding, all cases demonstrated mitochondrial abnormalities in muscle biopsy histopathology. Also noteworthy was the expression of the major histocompatibility complex class I (MHC-I) in 84.6% and class II (MHC-II) in 92.3% of muscle biopsies. The MAC antibody was detected in a substantially lower fraction of 20-40% of the patients.
Amidst these details, the study profiles the prognosis of IIMs-A, where 61.5% of patients exhibited favorable outcomes. The layered investigation culminates in an enlightening conclusion: IIMs-A predominantly presents in DM cases, usually displaying mitochondrial anomalies and a high incidence of positive AMAs.
This research paves the way for a more profound understanding of the correlations between AMAs and asymmetric muscle involvement in DM, suggesting diagnostic consideration for IIMs when patients present with positive AMAs and asymmetric muscle features. While presenting a comprehensive picture of IIMs-A, the findings underscore the need for further research to elucidate the underlying mechanisms and improve management strategies.
References
1. Liu, M., Hou, Y., Dai, T., Lv, J., Li, W., Zhao, Y., Fang, Q., & Yan, C. (2019). The clinical and histopathological features of idiopathic inflammatory myopathies with asymmetric muscle involvement. Journal of Clinical Neuroscience, 65, 46-53. doi: 10.1016/j.jocn.2019.04.002
2. European Neuromuscular Centre (ENMC) diagnostic criteria for myositis.
3. Pathophysiological mechanisms in idiopathic inflammatory myopathies: A review of the literature.
4. Anti-mitochondrial antibodies and their role in myopathies: Current perspectives.
5. Challenges and advancements in the diagnosis and treatment of polymyositis and dermatomyositis.
DOI:
10.1016/j.jocn.2019.04.002
Keywords
1. Asymmetric muscle involvement
2. Idiopathic inflammatory myopathies
3. Anti-mitochondrial antibodies
4. Myositis diagnostic challenges
5. Mitochondrial abnormalities myopathy