A descriptive study of patients with inflammatory myopathies at Tygerberg Academic Hospital and a review of current classifications

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Introduction: Idiopathic inflammatory myopathy (IIM) is a rare chronic disease of skeletal muscle. Determining its exact prevalence is complicated by the lack of uniformity of the definition and hence the classification of this condition. Therapeutic choices vary considerably because of the paucity of randomized controlled trials for this condition. Aims: To determine the prevalence of inflammatory myopathy in our drainage area, categorise our cases and to describe their extra-muscular and extra-cutaneous manifestations; to examine the utility of current classifications of IIM in our setting and propose an alternative classification; and to review the details and the effectiveness of the therapies given. Methods: A retrospective, cross-sectional, descriptive study was conducted. Information was obtained from the records of patients attending the clinic between January to June 2008. Demographic, clinical and laboratory data were extracted using a standardised data sheet. Results: Out of 1495 patients, 31 subjects with IIM were found. Estimated prevalence was 15.5 per million population. There were 28 females (90%) and 3 males (10%). The mean age of the patients was 45.2 years. Six (19.4%) had dermatomyositis (DM), 2 (6.5%) had polymyositis (PM) and 23 (74.2%) had connective tissue disease-associated myopathy (CAM). Muscle power in most patients was 4/5 (72.2%). Interstitial lung disease was the most common extra-muscular-/extra-cutaneous feature (25.8%). Antinuclear antibodies (ANA) were positive in 24 (77.4%) patients. There was a statistically significant difference of creatinine phosphokinase (CPK) levels between DM/PM versus CAM at presentation (p=0.024). Conclusion: IIM in our study population is more common compared to previous reports in the literature. CAM is the commonest cause by far, a finding not previously noted. Malignancy-associated inflammatory myopathy is rare. Studies evaluating the muscle biopsy findings in patients with CAM are required. There is a need for a new classification - we propose the umbrella term “auto-immune inflammatory myopathy”. We confirmed that IIM is a chronic debilitating condition requiring long term immunosuppressive therapy.
Idiopathic, Inflammatory myopathies, Classification, South Africa