# A Case of Cystic Neutrophilic Granulomatous Mastitis in Which Mycobacteroides abscessus Was Detected

## TL;DR

A rare case of breast inflammation caused by Mycobacteroides abscessus was successfully treated with drainage and antibiotics.

## Contribution

Reports a rare case linking Mycobacteroides abscessus to CNGM and suggests effective treatment strategies.

## Key findings

- Mycobacteroides abscessus was detected in a case of CNGM.
- Combination of drainage and antimicrobial therapy improved symptoms.
- No recurrence was observed 18 months after treatment.

## Abstract

Cystic neutrophilic granulomatous mastitis (CNGM) is characterized by granulomas with cysts that sometimes contain bacteria in the lumen, a surrounding neutrophilic infiltrate, and Langhans giant cells. There are no universally accepted diagnostic criteria for CNGM. Corynebacterium kroppenstedtii, a Gram-positive bacillus, has been reported to cause several infections, but the exact cause remains unclear. We report our experience with a case of CNGM, thought to be due to a rare Mycobacteroides abscessus infection.

We report the case of a 36-year-old Japanese woman with granulomatous mastitis due to Mycobacteroides abscessus who had not undergone surgery and was not immunosuppressed. She presented with a chief complaint of pain and swelling in her left breast for 1 month. Mammography showed asymmetrical focal increased density, and ultrasonography showed an irregular hypoechoic area in the left 3 o’clock position. Contrast-enhanced magnetic resonance imaging showed segmental non-mass-enhancement. Ultrasound-guided vacuum-assisted biopsy with pathology revealed granulomatous mastitis. Ziehl–Neelsen staining revealed red-staining bacilli. The patient was followed up for observation because her breast pain had decreased after the examination, and there was no redness or fever. However, the breast pain has not completely disappeared, and intermittent purulent discharge from the biopsy site persisted for 5 months. Hence, two 12-Fr drains were inserted along the ductal dilatation-like hypoechoic area. Imipenem, amikacin, and clarithromycin were administered for 8 days. After 8 days of this therapy, the patient developed a drug-associated rash; therefore, antimicrobial therapy was discontinued, and the drains were removed. Her symptoms improved, and magnetic resonance imaging after 1 month showed that the previous imaging findings in her left breast had disappeared. At the time of writing, 18 months have passed since treatment, and no recurrence has been observed.

We experienced a rare case of CNGM associated with Mycobacteroides abscessus. This case suggests that a combination of drainage and antimicrobial therapy may shorten the duration of antimicrobial therapy in CNGM.