Desmoplastic Neurotropic Melanoma Presenting as Pilonidal Sinus: A Rare Clinical Association.

BACKGROUND Pilonidal Sinus (PNS) is a small cutaneous orifice in the intergluteal region; symptoms include pain and swelling. Disparately, desmoplastic neurotropic melanoma (DNM) accounts for 1% of all melanomas and mostly occurs in the head and neck region. Because its appearance is generally benign, it typically comes to surgical attention only at an advanced stage or after recurrence. A perineural involvement occurs in 30-40% of the cases and is accompanied by symptoms such as paresthesia, paresis, and/or paralysis. To the best of our knowledge, the association between PNS and DNM has not been described in the literature before. Here, we present a patient with PNS that was diagnosed with DNM. CASE REPORT A 31-year-old healthy man presented with coccydynia and sacral cyst that had been present for about a year. While the initial diagnosis was of a PNS, after excision and biopsy, the pathology changed to PNS with DNM. The patient underwent a work-up for distant metastasis, which was negative. Wide local excision (WLE) with sentinel lymph node biopsy (SLNB) was also performed. CONCLUSIONS Due to the malignant potential of PNS, we support the routine of pathological examination of excised specimens. Once DNM is diagnosed, work-up for distant metastasis and further treatment with WLE as well as SLNB are recommended. The current report describes an association between PNS and DNM. While coccydynia may have been caused by the PNS or the melanoma, the presence of the PNS helped with an earlier diagnosis of the melanoma. Further research on the possible causative relationship between the conditions is required.