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NEOPLASMS

Subungual exostosis

Etiology and pathogenesis

Subungual exostosis is a variant of osteochondroma. Some argue that it is more correctly considered a reactive osseous outgrowth than a true tumor; in some cases, there is a clear history of preceding trauma. The male:female ratio of reported cases is 1:2. Average patients are in their twenties, but many teenagers are affected.

Clinical

The dorsal, medial aspect of the hallux is the most common site. The lesion appears as a pinkish nodule under the free end of the nail plate (Fig.29.34). Elevation and dystrophy of the overlying nail plate may occur.

Figure 29.34 Subungual exostosis. (a,b) A flesh-colored or hyperkeratotic nodule emanating from the subungual area of the great toe is characteristic.

Differential diagnosis

The diagnosis is made radiologically (Fig.29.35); the clinical differential diagnosis is listed in Table 29.3.

Figure 29.35 Subungual exostosis lifting the nail.

Treatment

This is surgical. One must avulse the nail; expose the exostosis via a longitudinal incision; and remove the exostosis, curetting the bone. This may require special surgical instruments. If distal enough, a subungual surgical approach may allow preservation of the nail (Fig.29.36).

Figure 29.36 Subungual exostosis lifting the nail.

Digital mucous (myxoid) cyst

Etiology and pathogenesis

The digital mucous cyst represents an accumulation of fluid just proximal to the nail (Figs 29.37–29.39; see also Figs 11.57 and 11.58). It is not a true cyst, as there is no wall. Some lesions communicate with the distal interphalangeal (DIP) joint.

Figure 29.37 Digital mucous cyst.

Figure 29.38 Digital mucous cyst. A clear, viscous fluid emanates on puncture.

Figure 29.39 Digital mucous cyst causing a groove in the nail plate.

Clinical

They present as a flesh-colored or translucent papulonodule on the dorsal part of a digit between the nail and the DIP joint. The fingers are much more commonly involved than the toes, and the lesions are usually solitary, but more than one can rarely be present (Fig.29.37). If punctured, clear viscous fluid may emanate, confirming the diagnosis (Fig.29.38). If the papule impinges on the nail matrix, a groove of the nail plate may form (Fig.25.39). Hemorrhage into the lesions may occur, turning them black. Subungual lesions may rarely occur on the nail matrix.

Differential diagnosis

Almost nothing else will appear as a translucent cyst in the periungual skin. Sometimes a groove will develop without an obvious cyst, but usually the cyst—although small—is there at the base. Occasionally, the bulk of the cyst will be below the nail, which may become thin and elevated. In all these situations, piercing the central point of the cyst with a needle and extruding clear, viscous fluid is diagnostic.

    Other growths or tumors that may occur periungually and could in unusual situations be confused with a digital mucous cyst include fibromas, warts, exostoses, and glomus tumor.

Treatment

No treatment has a high success rate, and some have significant morbidity, so explanation and reassurance may be sufficient. Some lesions are cured if the patient can be provided with several sterile needles and instructed how to drain the cyst. Alternatively, intralesional injection of a sclerosant or of triamcinolone (e.g. 5mg/mL) may be employed. Cryotherapy may work but requires long freeze times.

    Surgical excisions may also be done for lesions symptomatic enough to warrant excision. To be effective, this usually requires reflection of the proximal nail fold, with identification and cautery or ligation of any track back to the DIP joint. The main risks are stiffness (common) and postoperative mallet finger (uncommon, although fusion of the joint has occasionally been used for particularly troublesome cases). The CO₂ laser has also been used.

Glomus tumor

Glomus tumors are benign vascular lesions that arise from the neuromyoarterial apparatus. The glomus body from which they originate contains an afferent arteriole, a connecting vessel (Sucquet–Hoyer canal), a primary collecting vein, smooth muscle cells, and epithelial-type cells (glomus cells) surrounded by a fibrous capsule.

    A bluish red discoloration of the nail overlying a subungual papule is characteristic of a glomus tumor (Fig.29.40). Pain may occur spontaneously, after contact, or after change to a cooler temperature. Exact localization of the tumor may be difficult. Radiography may show bony erosion of the distal phalanx. Ultrasound and high-resolution magnetic resonance imaging (MRI) have been used. Excision is curative.

Figure 29.40 Glomus tumor. Note the red area just below the distal nail. Pain is often prominent.

Pyogenic granuloma

These are a rapidly growing vascular nodule that may be a response to an injury. The fingers are a typical site (see also Ch.15). They may cause a secondary nail dystrophy when they occur adjacent to the proximal nail fold (Fig. 29.41).

Figure 29.41 Pyogenic granuloma pressing down on nail matrix, inducing a groove. This patient was not on isotretinoin (which can predispose to this).

Fibrokeratomas

Multiple periungual fibrokeratomas are a key diagnostic feature in tuberous sclerosis (Ch.19). They may also occur as (usually solitary) acquired lesions that may be confused with warts. One variant of the acquired fibrokeratoma arises from the proximal nail fold, causing a nail groove and a conical projection running in the proximal part of the groove, and has been termed an invaginated fibrokeratoma.

PRACTICE POINTS

Malignant neoplasms

The most common malignant tumors that occur around the nail apparatus are as follows.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.