Subungual Hyperpigmented Nodular Lesion in an Adult's Toe

Upon physical examination, a well-delimited, 10-mm, hyperpigmented (dark brown) nodule, affecting the nail bed and hyponychium of the fifth right toe, was found ( fig. 1 ). Palpation evidenced hardened consistency. Upon physical examination of the entire body, the patient did not show any other lesions. The X-rays of the affected toe on its anterior-posterior and medium-lateral aspects did not show any bone changes. We chose to perform a shave biopsy ( fig. 2 ). What is your diagnosis? Question