Establishing National Guidance for Idiopathic Granulomatous Mastitis (ENIGMA): a scoping review of diagnostic practice.

AIMS: Idiopathic granulomatous mastitis (IGM) is a rare, benign inflammatory breast condition of unknown aetiology. It is a diagnosis of exclusion with a wide differential diagnosis. To date, no diagnostic guidelines exist for IGM in the UK. This scoping review aims to evaluate histopathological and microbiological approaches for the diagnosis of IGM.

METHODS: A scoping review was performed by conducting a search of MEDLINE, Embase and Cochrane databases from 2003 to 2023. Studies involving human participants with histopathologically confirmed IGM were included. Data on histopathological and microbiological investigations were extracted and analysed.

RESULTS: Out of 3208 search results, 225 studies involving 13 062 participants were included. Histological assessment was performed in 72.5% of participants, predominantly via core or excision biopsy. Microbiological investigations were inconsistently applied; only 47% of studies reporting the use of microscopy and culture. Only 24.9% of studies tested for tuberculosis using methods beyond histochemical Ziehl-Neelsen staining, and just 14 studies including 5% of participants described performing mycobacterial culture, despite this being the gold standard for diagnosis.was identified in several studies using advanced molecular techniques, suggesting possible misclassification of cystic neutrophilic granulomatous mastitis as IGM.

CONCLUSIONS: Substantial heterogeneity exists in the diagnostic workup for IGM, particularly in excluding infectious and systemic causes. Histopathology alone is insufficient for definitive diagnosis. A comprehensive, standardised diagnostic framework that incorporates clinical, microbiological and epidemiological factors is needed to improve diagnostic accuracy and ensure appropriate management, particularly in the context of possible immunosuppressive therapy.