The epidemiology of idiopathic inflammatory myopathies (IIMs) has been extensively studied out of Africa, but remains unclear in Africa. This is the first systematic review extensively addressing the epidemiology of IIMs in Africa.
We searched MEDLINE, EMBASE and African Journals Online for relevant studies published through December 30, 2020 . Data were combined via narrative synthesis. The review protocol was registered with PROSPERO, CRD42020186781.
Of 9918 records, 39 were included, reporting 683 cases (71.7% adults). The incidence of dermatomyositis (DM) was estimated at ~7.5/1,000,000 person years and 1.2/1,000,000 person years, and that of polymyositis (PM) was estimated at 8.8/1,000,000 person years. Prevalence rates of IIMs and PM subtype were estimated at 11.49/100,000 and 11/100,000 (95% confidence interval: 0-32), respectively. Mean age at diagnosis ranged from 7.9 to 57.2 years, and the female proportion from 50% to 100%. Main subtypes of IIMs in adults were DM (21%-93%) and PM (12%-79%), whereas DM (5.8%-9%) was the commonest juvenile IIM. 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 commonest myositis specific antibodies. Early mortality was high (7.8%-45%); main death causes being infections, cancers and damage accrual in respiratory and cardiovascular domains.
The epidemiology of IIMs in Africa seems similar to that from other continents, except for a potential much younger age at onset of adult IIMs in Africa. Further high-quality studies are needed.