An Atypical Presentation of Nodular Hidradenoma of the Thigh Treated With Mohs Micrographic Surgery.

Nodular hidradenoma (NH) is a benign adnexal tumor demonstrating both eccrine and apocrine differentiation. NH generally presents as a slow-growing, solitary, firm nodule, most commonly measuring 0.5-2 cm in diameter. It most frequently occurs on the scalp, thorax, abdomen, and gluteal regions, with a predilection for adult women in their fourth to eighth decades of life. We report the case of a 41-year-old immunocompetent female who presented with a red, 3.6 × 2.5 cm nodule on the left thigh. Due to the cystic nature of the lesion, it was initially presumed to be a benign cyst. However, as the lesion continued to grow slowly, a biopsy was performed, confirming the diagnosis of NH. Although malignant transformation is rare, it has been shown to follow an aggressive course with widely disseminated disease. Additionally, in some cases, it can be difficult to differentiate between NH and hidradenocarcinoma (HAC). Therefore, Mohs micrographic surgery (MMS) was performed to successfully remove the lesion with complete margin assessment. Currently, wide local excision (WLE) is the most common form of treatment. However, given the potential for malignancy and recurrence, we propose MMS as an alternative definitive treatment for NH, especially for tumors located in areas that would benefit from a skin-sparing surgical technique. This is among the few reported cases of NH affecting the thigh, highlighting the diagnostic challenges and the importance of considering NH in the differential diagnosis of atypical cutaneous nodules.