Chapter 17: Non-Melanocytic Nail Tumors

SUMMARY

• Non-melanocytic nail tumors (NMNT) herein reviewed are divided into: epithelial, fibrous, osteocartilaginous, and vascular tumors. They should be differentiated from pseudotumoral lesions, which include myxoid digital cyst, warts, onycholemmal or epidermal inclusion cysts, and from distant metastasis of extradigital cancers.

• These neoplasms can originate from any structure of the nail apparatus (matrix or proximal nail fold, nail bed and hyponychium) or arise from nearby tissue (distal phalanx, interphalangeal joints, vascular networks) and secondarily involve the nail.

TIPS FOR DIAGNOSIS

• The clinical presentation is conditioned by tumor location and evolution: malignant tumors have an aggressive behavior leading to the destruction and infiltration of nearby structures, whereas benign tumors tend to compress and distort the nail due to chronic pressure.

• Tumors arising in the peri-matricial space are the most challenging: if located above the matrix, they usually cause proximal paronychia and longitudinal grooving; if found under the matrix induce longitudinal ridging and fissuring. In both cases, distal splitting may occur.

• Acquired single-digit deformities, including Hippocratic nail, could be the first sign of nail cancer.

TIPS FOR TREATMENT

• The treatment of NMNT is electively surgical. Tumor enucleation is performed through classic or tangential longitudinal excision according to the degree of local invasion and tumor behavior. Mohs surgery is always advisable for malignant tumors as it saves healthy tissue and controls margins; if not feasible, radical excision of the nail unit with 5-mm surgical margins is recommended for Bowen disease and early squamous cell carcinoma. Bone curettage is performed for exostosis, whereas amputation of the distal phalanx is recommended for advanced squamous cell carcinoma with bony involvement.

• CO₂ laser vaporization and cryotherapy are burdened by the high risk of recurrence due to uncontrolled margins. Medical administration of cytostatic (oral acitretin, intralesional methotrexate, or intralesional bleomycin) or immunoregulatory drugs (imiquimod) can be considered respectively in case of keratoacanthoma and Bowen disease. Topical rapamycin is used for Koenen’s tumors in patients affected by tuberous sclerosis.

DON’T FORGET

• Patients of any age could develop specific NMNT.

• Early-onset and polydactylous NMNT require genetic counseling to rule out hereditary disease.

• Always inspect the distal edge with the dermoscope, especially when concomitant abnormalities of the nail plate are present.

PITFALLS AND CAUTIONS

• Do not minimize patients’ symptoms in the case of negative examination: remember that most subungual NMNT grow silently before being clinically manifest.

• Be cautious when interpreting the pathological results of a preliminary biopsy for malignant neoplasms, as foci of tumor invasion can be missed in a punch biopsy.

• Neoplasms with a band-longitudinal presentation mimic inflammatory disease as lichen planus or melanocytic nail lesions, which need to be ruled out.

EXPERT PEARLS

• Clues for malignancy are exacerbating tenderness, single-digit involvement, progressive loss of nail plate, soft tissue swelling, sudden onset of chromonychia, nail plate distortion, localized subungual hyperkeratosis at the distal end.

• Clip the nail plate in case of localized onycholysis to unravel ...