Painful eccrine spiradenoma containing nerve fibers in the forearm: a case report

Eccrine spiradenomas are rare benign adnexal tumors that originate from the eccrine glands. They mainly arise in the head, neck, and upper trunk of young adults and are sometimes accompanied by pain and tenderness. Although spontaneous pain is a typical symptom of eccrine spiradenoma, the underlying mechanism remains unclear. We report the case of a patient who had a spiradenoma in the subcutaneous tissue of the left forearm that was accompanied by agonizing pain triggered by pressure. A 42-year-old man who had undergone surgical excision of a left forearm mass 5 years ago presented for relapsed pain and a palpable mass at the previous excision site. The agonizing pain had been triggered a few days ago, in response to even a slight touch. The mass measured approximately 0.8×0.8 mm, and ther e were no changes visible around the scar. Irregularly shaped masses, each measuring approximately 5 mm, were removed with a 2-mm safety margin from the subcutaneous fat. A histopathologic examination revealed the resected nodules were surrounded by delicate fibrous capsules, some parts of which contained blood vessels and prominent thickened nerve fibers. By the time of the 6-month follow-up, the masses had not recurred, and the biopsy site was well maintained without pain. We describe the surgical and histopathologic findings of an isolated eccrine spiradenoma accompanied by recurrent agonizing pain. The peculiar microscopic arrangement of the thickened nerve fibers encasing the nodule of eccrine spiradenoma may correlate with its pain mechanism.