Squamous cell carcinoma of the nail unit

Abstract

Squamous cell carcinoma (SCC) of the nail apparatus is a rare malignant tumor that usually originates underneath the nail plate and grows slowly with possible bone invasion. The etiology remains unknown, although a strong association with different conditions, such as high-risk human papillomavirus (HPVs), trauma, or radiation exposure has been demonstrated. Nail SCC is called "the great mimicker nail tumor" because different clinical presentations may coexist, resembling benign or malignant nail lesions. For this reason, there is often a significant delay between the onset of nail SCC and the diagnosis. Clinical manifestation includes onycholysis and erythema, while in the advanced stages nail ulceration can be observed. The association with pain, swelling, and inflammation usually indicates an invasive SCC with involvement of the underlying bone. Metastasis is rare but possible with involvement of lymph nodes. A multidisciplinary approach to assessment, management, and follow-up is advised. Using careful examination and modern diagnostic methods, including onychoscopy, biopsy, and histopathology, will help identify SCC and prevent the invasive progression. X-ray is important to investigate the bone invasion to determine the best surgical approach that will have satisfying cosmetic and functional outcomes. Nevertheless, local excision with sufficient surgical margins, best if using Mohs surgery, is usually sufficient and superior to amputation of the distal phalanx. This review aims to highlight the correct approach in suspected SCC of the nail unit.

Keywords: malignant nail tumor; nail surgery; nail unit; onychoscopy; squamous cell carcinoma.

Figure 1

SCC with lateral detachment of the nail and a warty aspect of the exposed nail bed and lateral nail fold with black discoloration that tends to ulcerate with a scab formation. [Copyright: ©2018 Starace et al.]

Figure 2

SCC with lateral verrucous lesion, frequently misdiagnosed as viral wart especially when the lesion is characterized by nail plate partial or total absence due to a hyperkeratotic nodule. [Copyright: ©2018 Starace et al.]

Figure 3

SCC with eroded mass under the nail, characterized by onycholytic area with oozing from the nail in late stage due to subungual erosion. [Copyright: ©2018 Starace et al.]

Figure 4

SCC long-standing subungual lesion, evolving in nail bed large erosion with disappearing of nail plate. [Copyright: ©2018 Starace et al.]

Figure 5

SCC with a longitudinal erythronychia and erosion of under nail bed. [Copyright: ©2018 Starace et al.]

Figure 6

Clinical picture in (A) frontal view and (B) lateral view of SCC and onychoscopy of typical alterations of SCC: onycholysis, irregular vascularity, and erosion of nail bed (C) before and (D) after nail clipping onycholytic nail plate. [Copyright: ©2018 Starace et al.]

Figure 7

Onychoscopy of a verruca-like aspect of SCC: onycholysis, irregular vascularity, and hemorrhage, verrucous surface of nail bed. [Copyright: ©2018 Starace et al.]