Cystic neutrophilic granulomatous mastitis associated with Corynebacterium: A systematic review of clinical, pathological, and therapeutic insights

Cystic neutrophilic granulomatous mastitis (CNGM) is a rare and underrecognized subtype of granulomatous mastitis, increasingly associated with Corynebacterium species, particularly Corynebacterium kroppenstedtii. Despite a growing number of reports, its diagnosis remains challenging, and treatment approaches are highly variable.

This systematic review aimed to consolidate the clinical, microbiological, and therapeutic characteristics of CNGM to better inform clinical management. A structured search of PubMed using MeSH terms identified 13 studies, of which 11 met inclusion criteria.

These studies, encompassing 387 patients, were analyzed for clinical presentation, diagnostic methods, histopathological findings, bacterial species, antimicrobial susceptibility, treatment strategies, and outcomes. CNGM typically presented as a unilateral painful breast mass, frequently accompanied by abscess, nipple inversion, or fistulae. Diagnosis was established via histopathology and confirmed by microbiological testing, often through MALDI-TOFMS or 16S rRNA sequencing. While C. kroppenstedtii was most frequently isolated, recent studies suggest C. parakroppenstedtii may be more prevalent than previously recognized. Antimicrobial susceptibility data revealed consistent resistance to beta-lactams and variable susceptibility to clindamycin and fluoroquinolones, whereas linezolid and vancomycin demonstrated consistent efficacy. Directed antibiotic therapy, particularly with lipophilic agents, combined with abscess drainage, was associated with improved outcomes and lower recurrence. In contrast, higher recurrence rates were reported with corticosteroids or immunosuppressants used in isolation.

These findings support a multimodal approach as the most effective strategy for CNGM management. Further prospective studies are needed to establish standardized diagnostic criteria and evidence-based treatment guidelines.