1. Presented by Nicholas Rogers, MD and reviewed by Nicole Parrish, PhD.

A middle-aged patient with no significant past medical history presents with a pink, scaly, red papule on a finger (Figure 1). The papule has been present for approximately one year and has been growing slowly over that time. The lesion appeared a few weeks after the patient accidently cut their finger, with concurrent exposure to marine water. Laboratory studies including CBC and CMP were unremarkable. No lymphadenopathy or additional skin lesions were noted on physical exam. A biopsy was performed that showed granulomatous and neutrophilic inflammation concerning for an infectious process (Figure 2). PAS, GMS, and AFB stains were negative for microorganisms. A portion of the biopsy was also sent to microbiology where Auramine-Rhodamine and calcofluor white stains were negative.

Figure 1


Figure 2

Question: What is the most likely cause of this lesion?