Epidemiology of idiopathic inflammatory myopathies in Africa: A contemporary systematic review

Method

We registered the protocol with PROSPERO, CRD42020186781. PRISMA guidelines were applied to report this review. Studies addressing the epidemiology of IIMs in Africa and released before 30 December 2020, were searched for in electronic databases (MEDLINE, EMBASE and African Journals Online) and manually. Case series involving fewer than 9 participants, studies focusing on IIMs in pregnant women, articles lacking primary data, duplicate articles reporting on the smallest sample size of a study, as well as articles whose full-texts were not available after three requests from authors, were excluded. The risk of bias of each included study was assessed using Hoy et al’s criteria. Due to high between-study heterogeneity, we opted for a narrative data synthesis.

Data

39 of 9918 identified records were included. Studies were conducted in 19 countries between 1958 and 2019, and came from across all United Nations Statistics Division African regions:  Northern Africa (n = 18), Western Africa (n = 10), Southern Africa (n = 5), Eastern Africa (n = 4) and Central Africa (n =2). These studies reported 683 cases (607 adults and 76 children and adolescents) of IIMs, 50% to 100% being female subjects. The mean age at diagnosis varied between 7.9 and 57.2 years: 7.9-11 for juvenile IIMs and 20–57.2 for adult IIMs.

Incidence of DM was estimated at ~7.5/1,000,000 person years and 1.2/1,000,000 person years. The incidence of PM was estimated at 8.8/1,000,000 person years. The prevalence of combined IIMs was estimated at 11.49/100,000 and that of PM was estimated at 11/100,000 (95% confidence interval: 0-32). Main subtypes of adult-onset IIMs were DM (21%-93%) and PM (12%-79%), whereas the commonest young-onset subtype was juvenile DM (5.8%-9%). Skeletal muscle involvement (56%-100%) was the main disease feature, and oesophagus the most commonly affected internal organ (6%-65.2%). Anti-Jo1/histidyl tRNA synthetase (7%-100%) and anti-Mi2 (17%-45%) antibodies were the most frequent myositis specific antibodies. Glucocorticoids were the first-line prescribed treatment, and methotrexate the preferred glucocorticoid -sparing drug. Early mortality was high (7.8%-45%) and main death causes were infections, cancers and organ damage in respiratory and cardiovascular domains.

Conclusion

Based on current data, the epidemiology of IIMs in Africa is similar to that in other regions, except for the age of onset of adult IIMs which seems much younger than in other regions. These findings require confirmation from more high-quality studies.