Ulcer and Subcutaneous Nodules

Enlarging tender ulcer on right hand

A 19-year-old man presented to the dermatology clinic with a 3-month history of an enlarging ulcer on his right hand and multiple tender subcutaneous nodules on the right forearm and elbow. Five months earlier, he had traveled to Ecuador, and worked on an organic produce farm. On physical examination, the ulcer measured 3 cm in diameter and was tender with a firm border.

What is the most likely diagnosis?