28.2.8 Extensor Tendon

The extensor tendon attaches onto the dorsal proximal end of the distal phalanx just proximal to the nail matrix. This tendon thins out as it attaches onto the bone.

Summary: Tumors

•Nail unit tumors are rare entities, with Bowen’s disease carcinomas, in our experience, being the most frequent tumor of the nail unit.

•Involvement of the bone by the tumor precludes Mohs surgery. When there is tumor invasion into the bone, the patient should be evaluated for management by a hand surgeon.

•For tumors of the nail unit without bone involvement, their removal by Mohs surgery is ideal. Mohs surgery removes affected tissue and allows for maximum normal tissue preservation.

28.3Tumors

28.3.1 Squamous Cell Carcinoma

Among the nail unit malignancies in the upper and lower extremities, squamous cell carcinoma is the most frequently reported. A squamous cell carcinoma of the nail unit is considered a low-grade malignancy with a good prognosis. While this carcinoma rarely metastases [4], it can invade the distal phalanx. Extensive disease, which can be due to poor differentiation of the primary tumor or increased depth of tumor invasion, may require amputation and lymph node dissection [5].

Squamous cell carcinoma of the nail unit most commonly affects the thumb, which can result in significant hand disability if amputation of the affected digit is required. Polydactylous disease is commonly due to an environmental exposure, as the condition must develop independently in each digit [6, 7]. Some causes of squamous cell carcinoma of the digits include: solar radiation, arsenic, x-ray radiation, tar, or warts (particularly human papillomavirus 16 exposure) [6, 8, 9]. Besides surgery, treatment modalities for squamous cell carcinoma of the nail unit include: radiation [10, 11], photodynamic therapy [12], or the CO2 laser [13].

Squamous cell carcinoma of the digit and nail unit often present as a nonspecific irritation and may be mis-

diagnosed as onychomycosis, paronychia, or eczema. Skin ulceration, onycholysis, and nail plate destruction may occur over time due to the delayed diagnosis. Keratoacanthomas of the nail bed or matrix are typically diagnosed early, as compression of this rapidly growing tumor between the nail plate and the bone causes great pain. A radiograph of the affected digit may be useful prior to Mohs surgery, as the radiograph can inform the surgeon whether there is tumor invasion into bone. Caution is warranted, however, as inflammation and infection create a radiologic image suggestive of tumor invasion when true tumor invasion is not present [8, 9, 14]. Additionally, some authors have noted periosteal tumor invasion despite a normal radiograph [8, 9]. De Berker et al. described the removal of a portion of the distal phalanx and decalcification of the bone for 48 h and then embedding the tissue in permanent paraffin blocks to rule out tumor invasion into the bone [9]. If definitive bone involvement has occurred, amputation of the affected digit by a hand surgeon along the metacar- pal-phalangeal joint is recommended, or amputation at the interphalangeal joint proximal to bone invasion as seen by radiograph [2, 14]. For squamous cell carcinomas not involving the bone, Mohs surgery is a preferred treatment option and provides the highest cure rate along with the greatest amount of tissue preservation compared to other treatment modalities (see Fig. 28.1a–c).

28.3.2 Bowen’s Disease

Due to its distinct histologic appearance, Bowen’s disease is categorized separately from squamous cell carcinoma by some, but not all authors. Dysplastic changes consisting of cellular atypia, loss of epidermal polarity, and large bowenoid cells may be seen within the entire thickness of the epidermis. Sometimes these changes are more subtle and do not involve the entire epidermal thickness. However, Bowen’s disease may also invade the dermis, and Mohs surgery can be quite useful in determining such invasion (see Fig. 28.2). Thus when using Mohs surgery to excise Bowen’s disease carcinoma in this area, high slide quality is extremely important. As opposed to squamous cell carcinomas, keratin pearls are absent. It is also felt that the keratinizing variants of squamous cell carcinomas may be more aggressive than the bowenoid variants [6]. Bowen’s disease generally presents as a scaly path of the nail folds (see Fig. 28.5c), but has also been reported to present as mel-

Fig. 28.1 (a) Squamous cell carcinoma along lateral nail fold of the right first toe. (b) Wound after final Mohs surgery stage. Note bone exposure in center of wound. (c) Healed result 1 year postoperatively

anonychia [15]. It has been treated by CO2 laser vaporization by some investigators [13]. However, we feel Mohs surgery offers the patient the highest likelihood of cure, because as previously stated, these tumors can be quite subtle, histologically (see Fig. 28.3a–d). Unlike non-Bowen’s squamous cell carcinoma, Bowen’s disease carcinoma in the periungual location is frequently associated with oncogenic human papillomavirus.

28.3.3 Melanoma

Malignant melanoma of the subungual location is uncommon and accounts for 2–3% of all cutaneous melanomas in Caucasian populations and 20% in African and Asian populations [16–19]. Patient prognosis depends on early detection, and this is particularly true of subungual melanomas. Blessing evaluated 100 cases of subungual melanomas; the mean Breslow depth of the patients was 4.7 mm, and greater than 70% of the cases were staged Clark IV or V at onset [16]. Metastases to the epitrochlear and axillary nodes are common because of delayed diagnosis [20]. Due to the aggressiveness of this disease and its delayed diagnosis averaging 2 years after the initial presentation, the 5-year survival for a subungual melanoma is 50% or less [21]. Moehrle et al. evaluated 73 patients with subungual melanomas and found that at the time of diagnosis, 4.1% (3 patients) had in-transit metastasis and 11% (8 patients) had regional lymph node metastasis [22].

Subungual melanoma most commonly occurs between the sixth and seventh decades of life [19] and is often misdiagnosed as a subungual hematoma, pyogenic granuloma, chronic paronychia, or onychomycosis. When diagnosed, subungual melanomas are more often located on the thumb (58%) compared to the other fingers and the hallux (86%) compared to the other toes [18, 23]. The prevalence of subungual melanomas on the thumbs and great toes can be devastating for patient, as these are the most used digits [22]. Unfortunately, 20% of subungual melanomas are amelanotic, which can make diagnosis difficult [21]. The classic presentation of a melanoma involving the nail matrix is seen with “Hutchinson’s sign,” which is pigmentation along the proximal nail fold at the end of a pigmented nail streak [20]. With time, melanoma may become darker, nodular, and even ulcerate. If the melanoma is localized, traditional surgery is a wide local excision, which can result in complete amputation of the affected digit. Green’s 20th edition of Operative Hand Surgery recommends amputation for a subungual melanoma 1 joint more proximal to the joint closest to the melanoma [24]. Amputations have also been recommended at the level of the metacarpal/ metatarsal bones or at the metatarsophalangeal or metacarpophalangeal joints and possible lymph node dissection [17, 19].

The application of Mohs surgery has been used for melanomas involving the nail unit. Brodland presented

14 cases of a nail apparatus treated with Mohs surgery [25]. One particular benefit of Mohs surgery in the treatment of melanomas is that more tissue is examined than with standard surgical excision; thus subtle areas of melanoma invasion may be identified. For example, in the case reported by Do et al., a biopsy-proven melanoma in situ was treated with Mohs surgery. During surgery, an invasive component was identified that resulted in a partial amputation of the digit [26]. We believe melanoma in situ of the nail bed is easily treated with Mohs surgery and can avoid amputation for the patient, which may occur with traditional surgery (see Fig. 28.4a–c). However, melanoma in situ of the nail bed can be subtle in its histologic appearance, and thus high-quality frozen sections are necessary to provide the patient with the best possible cure rate.

28.3.4 Basal Cell Carcinoma

Nail unit basal cell carcinomas are rare and more commonly occur on the fingers than on the toes [27, 28]. The rarity of basal cell carcinomas on the fingernail unit, despite the amount of sun exposure on the hands, is attributed to the lack of pilosebaceous units in this region. Ultraviolet radiation is still felt to be a contributing factor, however, along with chronic trauma and

arsenic [29].The variable clinical presentation of nail unit basal cell carcinomas makes diagnosis difficult, and patients may be misdiagnosed for many months until a biopsy is performed. Prior to the diagnostic biopsy, common clinical diagnoses include: an eczematous process, chronic paronychia, pyogenic granuloma, psoriasis, chronic ulcer, onychomycosis, longitudinal melanonychia, or even acral melanoma.

Treatment for basal cell carcinomas involving the nail unit has included radiation, curettage followed by salicyclic acid and podophyllin application [30], curettage with grenz rays [31], Mohs surgery, wide local excision, and amputation.

28.3.5 Warts

Warts are benign tumors induced by human papilloma virus. The most common site for ungual warts is along the lateral nail fold [4]. When the wart grows beneath the nail plate, onycholysis and nail dystrophy can occur. Periungual warts are felt to be inoculated by trauma and may be mistaken for other conditions, such as Bowen’s disease or squamous cell carcinoma [4]. For treatment of subungual warts, care must be made to avoid damaging the nail matrix; otherwise nail plate dystrophy can

Fig. 28.3 (a) Bowen’s disease carcinoma of left medial (radial) lateral nail fold of the fourth finger. (b) Bowen’s disease carcinoma of the nail bed. Note the atypical cells longitudinally

arranged corresponding to the nail bed ridges. (c) Postoperative appearance after Mohs surgery. Note bone exposure in center of wound. (d) Healed result 1 year postoperatively

occur. Although benign, periungual warts can be persistent, painful, and recurrent despite meticulous treatment attempts. We have treated such warts suc-

cessfully with Mohs surgery and feel this treatment modality has a place in the management of periungual warts.