Idiopathic granulomatous mastitis: A scoping review to determine the quality and geography of the evidence base.

Idiopathic granulomatous mastitis is a rare chronic inflammatory breast condition with uncertain aetiology, inconsistent diagnostic pathways, and variable treatment practices. This scoping review aims to map the breadth, geographical origins, and methodological quality of the current published literature, thereby evaluating its strength and applicability in guiding clinical practice in the United Kingdom and similar healthcare systems. A literature search on March 9th 2023 revealed 3208 records: 225 primary studies and five systematic reviews met inclusion criteria. The primary studies reported on 13,062 patients from 39 countries, with Turkey represented most. Studies were predominantly retrospective and single-centre, with small sample sizes. Fifteen authors appeared on multiple papers; assessment of these publications showed that 24 papers, encompassing 2242 patients (17.2% of all patients), may have overlapping cohorts. Of the 225 primary studies, 175 (77.8%) reported at least one treatment or intervention. When appraised using the Oxford Centre for Evidence Based Medicine criteria for treatment benefit, most evidence (122 studies, 69.7%) was level four (e.g. case series). A further 50 studies (28.6%) provided level three evidence (e.g. non-randomised follow-up studies), and only three studies (1.7%) were randomised controlled trials, representing level two evidence. No studies could be categorised as level one (highest strength of evidence). The systematic reviews included 6262 patients across overlapping primary studies, and incomplete referencing in one review prevented accurate cross-matching between the reviews and with the primary studies. Overall, current evidence is geographically concentrated, methodologically weak, and insufficient to guide practice. High-quality prospective and randomised studies are urgently required.