Wolf in Sheep’s Clothing: Squamous Cell Carcinoma of the Nail Bed

Dear Editor, A 93-year-old man presented with a nonhealing ulcer over the right thumb of 1 year duration. He complained of the gradual onset of a small ulcer underneath the nail of the right thumb. It was associated with swelling and minimal pain. After 4 months of onset, he consulted a surgeon who managed him as a case of chronic paronychia and performed a nail avulsion but the ulcer did not heal but gradually increased in size leading to the destruction of the overlying nail plate till he presented to us. Dermatological examination revealed a tender ulcer of 2.5 cm × 1.5 cm size at the distal end of the right thumb nail bed with the destruction of the overlying nail plate extending onto the lateral nail fold [Figure 1a]. The floor of the ulcer showed healthy granulation tissue. The locoregional lymph nodes were not enlarged. Histopathology on the biopsy specimen from the ulcer revealed focal full-thickness dysplasia of the epithelial lining [Figure 1b]. The subepithelium showed the presence of atypical cells with loss of polarity [Figure 1c], high nucleo: cytoplasmic ratio, and nuclear atypia [Figure 1d]. Squamoid differentiation was noted with occasional mitotic activity. The squamoid origin of the malignant cells was confirmed by P40 [Figure 1e]. Magnetic resonance imaging of the thumb ruled out any bony involvement. Positron emission tomography-computed tomography did not highlight any locoregional lymph nodes or distant metastasis. The patient was diagnosed as a case of microinvasive squamous cell carcinoma (SCC) of the nail bed of the right thumb. He was referred to a surgical oncologist for further management.Figure 1: (a) An ulcer on the distal end of the thumb measuring 2.5 cm × 1.5 cm destroying the overlying nail plate. (b) Photomicrograph of the biopsy specimen from the ulcer showing focal full-thickness dysplasia of the epithelial lining. (c) The subepithelium shows the presence of atypical cells with loss of polarity. (d) Squamoid differentiation with high nucleo: cytoplasmic ratio, nuclear atypia, and occasional mitotic activity. The squamoid origin of the malignant cells was confirmed by P40, (e) (×4, 10, 40, H and E, P40)Despite being the most common primary malignant neoplasm of the nail bed, SCC of the nail bed is rare.[1] Diagnosis is often delayed since unlike SCCs in other parts of the body, SCC at the nail bed progresses/ulcerates gradually and is further obscured by the nail plate. Since it mimics commoner diseases such as chronic paronychia and subungual warts, the diagnosis is often or missed for months and even years.[2] Some patients undergo repeated sittings of nail plate avulsion and cauterization before a biopsy is done for the definitive diagnosis of the SCC. The thumb is the most commonly affected digit as seen in our case.[3] The etiology is uncertain but trauma and human papillomavirus infection are believed to be the most putative triggers.[4] Fortunately, SCC of the nail bed is less aggressive than SCC arising in other parts of the body.[5] Involvement of axillary lymph node and distant metastasis are infrequent as seen in our patient. The choice of treatment depends on the extent of the locally invasive lesion and metastasis. Moh’s micrographic surgery is preferred in lesions without bone involvement.[1] In case the procedure is not accessible, a wide local excision and repair by flap may also be done. For invasive tumors involving the bone, digital amputation is indicated. To conclude, a high degree of suspicion for SCC must be maintained in elderly patients presenting with a chronic nonhealing ulcer on the nail bed, not responding to antifungal therapy, repeated nail plate avulsion, and cauterization. In such cases, a biopsy must be done to rule out SCC. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.