Cystic Neutrophilic and Granulomatous Dermatitis as the Cutaneous Counterpart of Cystic Neutrophilic and Granulomatous Mastitis: A Case Series.

Cystic neutrophilic granulomatous mastitis (CNGM) has a distinctive morphology characterized by small cystic spaces with a concentric rim of primarily neutrophils and epithelioid histiocytes. These cystic spaces have a granular basophilic quality; a Gram stain discloses gram-positive bacilli compatible with a Corynebacterium species with the most common isolate being Corynebacterium kroppenstedtii. We identified 16 cases of Corynebacterium related cystic neutrophilic granulomatous dermatitis (CNGD) within our dermatopathology database. The histology in all cases was reproducible being in the context of small microcystic foci surrounded by neutrophils and mononuclear cells. Gram-positive coccobacillary forms were found within the center of the microcysts in a number of the cases. Facial cases are likely reflective of the high concentration of Demodex on the face and could be a further manifestation of a rosacea like diathesis as the natural bacterial endosymbiont for Demodex is Corynebacterium kroppenstedtii. The development of this distinctive cutaneous infection in parts of the body without a high concentration of Demodex could be a sign of impaired immunity. Other potential infectious causes of ringed granulomatous inflammation in the skin would primarily be limited to lipophilic organisms such as Cutibacterium acnes, Malassezia furfur, Bacillus licheniformis, Coxiella burnetti and certain lipid rich fungal organisms, best exemplified by cryptococcosis.