Two Cases of Granulomatous Mastitis Caused by Corynebacterium kroppenstedtii Infection in Nulliparous Young Women with Hyperprolactinemia.

Recently, an association between granulomatous mastitis and local infection with Corynebacterium (C.) kroppenstedtii has been suggested. We herein report two cases of granulomatous mastitis resulting from C. kroppenstedtii infection in nulliparous young women with hyperprolactinemia. Both cases involved nulliparous patients with drug-induced hyperprolactinemia, and both individuals received incision and drainage, after which the pus was sent to our laboratory. Corynebacterium spp. grew on blood agar, and 16S rRNA gene sequencing identified the pathogen as C. kroppenstedtii. In conclusion, lactational changes caused by drug-induced hyperprolactinemia may increase the risk of granulomatous mastitis after C. kroppenstedtii infection.