Pure Bullous Pyoderma Gangrenosum, a Challenging Clinico-Pathological Diagnosis: Critical Literature Review with Emphasis on Diagnostic Criteria.

Pyoderma gangrenosum (PG) is an uncommon, idiopathic, neutrophilic dermatosis characterised by large necrotic ulcers. Occasionally, patients develop atypical presentations, including pustular, bullous, and vegetative lesions. Bullous pyoderma gangrenosum (BPG) is considered an extremely rare form. We describe a case of BPG in a 76-year-old man, with active oncological history, including a recent diagnosis of hairy cell leukemia. Diagnosis of PG was delayed because of atypical clinical presentation that mimicked necrotising fasciitis. The patient was treated with diverse intravenous antibiotics and several surgical procedures. The suspicion of neutrophilic dermatosis arose from the histopathological studies. In the setting of mandatory clinico-pathological correlation, the aim of this report is to point out the morphological characteristics that allow recognition of this uncommon variant of pyoderma gangrenosum.