Out of 374 titles identified, we removed 100 duplicates, and screened 274 titles and abstracts. Of those, 67 articles were reviewed at full text and 29 studies were included in the review as shown in Fig. 1.

Selection flow chart of studies included in the systematic review

Included studies are summarised in Table 2 and a full data extraction table is presented in Supplementary Table 1. The 29 included studies comprised 24 non-comparative descriptive studies (including 15 case reports [25,26,27,28,29,30,31,32,33,34,35,36,37,38,39], five case series [40,41,42,43,44], two surveys [45, 46], and two descriptive cross-sectional studies [2, 47]), and five comparative studies (all analytical cross-sectional studies) [9, 48,49,50,51]. Twenty-eight of the included studies used non-patient-reported data including clinical reports and retrospective patient registry data, while one used patient-reported data [45]. In total, there were eleven studies from Europe [2, 9, 25, 26, 33, 35, 38, 42, 45, 47, 48], nine from the United States or Canada [27, 29, 30, 32, 34, 37, 43, 44, 49], three from West Asia [41, 46, 50], four from East Asia [28, 31, 39, 40], one from sub-Saharan Africa [36], and one from South America [51]. Various organ involvement of sarcoidosis was reported, including eyes [9], nasal passages [42], kidney [26, 27], skin [28, 34], heart [40, 48], nervous system [30, 38, 44], lungs [35,36,37, 43], skeletal muscle [33], subcutaneous tissue [39], and systemic or mixed [2, 25, 29, 31, 32, 41, 45, 46, 49,50,51]. Based on the manual categorisation, thirteen studies examined extrapulmonary sarcoidosis [26,27,28,29,30, 32,33,34, 39, 40, 44, 47, 48], five examined systemic sarcoidosis [9, 25, 31, 38, 42], and four examined pulmonary sarcoidosis [35,36,37, 43]. In seven studies it was not possible to differentiate between pulmonary and non-pulmonary sarcoidosis [2, 41, 45, 46, 49,50,51]. Of the 29 included studies, 18 were from countries with non-gatekeeper health systems (2, 25, 27–33, 3537, 39, 40, 43, 44, 47, 49) and 11 were from countries with gatekeeper health systems [9, 26, 34, 38, 41, 42, 45, 46, 48, 50, 51]. Twelve studies reported data on ethnicity or race [2, 25, 29,30,31,32,33, 36, 42, 43, 49, 51].

In total, a population size of 1531 participants (694 females; 837 males) was included in the review. The mean age was 47.91 years (SD = 5.47), excluding case reports (see below). Overall, participant ages ranged from 9.3 years to 69 years (including case reports).

Consensus on the quality appraisal of the included studies is shown in Supplementary Table 2. After the double-quality appraisal, a consensus was reached by two authors regarding an overall low risk of bias for all studies; therefore, no study was excluded.

Twenty case studies comprising 15 case reports (8 females; 7 males) [25,26,27,28,29,30,31,32,33,