Fibromas

Many different types of fibroma may occur in and around the nail (Figure 5.19). They may be true entities or merely variants of one process.

Keloids

Hypertrophic scars and keloids result from injuries to the nail fold or nail bed and may significantly distort the nail apparatus.

Dermatofibroma

Nail apparatus dermatofibromas are rare and may resemble cutaneous horns, fibrokeratomas or supernumerary digits; the latter, however, usually arise on the ulnar aspect of the fifth metacarpophalangeal joint. The histological changes include areas of thick, hypocellular, hyalinized collagen bundles, randomly orientated; there is an ill-defined nodule situated mainly in the reticular dermis; elastic fibres are often scarce or absent.

Koenen's tumour

Koenen's periungual fibromas develop in 50% of cases of tuberous sclerosis (epiloia or Bourneville-Pringle disease). They usually appear at about 12-14 years of age and increase progressively in size and number with age. Individual tumours are small, round, flesh-coloured and asymptomatic, with a smooth surface (Figures 5.20, 5.21). The tip may be slightly hyperkeratotic, resembling fibrokeratoma. The tumors grow out from the nail fold, eventually overgrowing the nail bed and destroying the nail plate. Depending on their site of origin, they may cause longitudinal depressions in the nail plate. Excessively large tumours are often painful, requiring excision. Histological changes consist of dense angiofibrotic tissue, sometimes with neuroglial tissue at the centre, and hyperkeratosis at the tip.

Figure 5.19

Periungual fibroma. (Courtesy of Akiro Kamumochi, Japan.)

Figure 5.19

Periungual fibroma. (Courtesy of Akiro Kamumochi, Japan.)

Figure 5.20

Koenen's tumour associated with nail plate destruction.

Figure 5.20

Koenen's tumour associated with nail plate destruction.

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Figure 5.21

Multiple Koenen's tumours.

Koenen's tumours are cured by simple excision. Usually no suture is necessary. Tumours growing out from under the proximal nail fold are removed after reflecting the proximal nail fold back by making lateral incisions down each margin in the axis of the lateral nail grooves. Subungual fibromas are removed after avulsion of the corresponding part of the nail plate.

Acquired periungual fibrokeratoma

Acquired periungual fibrokeratomas are probably identical to acquired digital fibrokeratomas and Steel's 'garlic clove' fibroma. They are acquired, benign, spontaneously developing, asymptomatic nodules with a hyperkeratotic tip and a narrow base (Figures 5.22, 5.23). They most commonly occur in the periungual area or on other parts of the fingers. A case was described in which the lesion was located beneath the nail, visible under the free margin of the great toe nail. Most periungual fibrokeratomas emerge from the most proximal part of the nail sulcus growing on the nail and causing a sharp longitudinal depression. Trauma is thought to be a major factor initiating acquired periungual fibrokeratoma.

Microscopically, acquired periungual fibrokeratomas resemble hyperkeratotic 'dermal hernias'. The core consists of mature eosinophilic collagen fibres oriented along the main vertical axis of the tumour. The fibroblastic cells are increased in number. Most fibromas are highly vascular. The epidermis is thick and acanthotic. There is a marked orthokeratotic horny layer, which may be parakeratotic and contains serum or blood at the tip of the tumour. Elastic fibres are normal. Acid mucopolysaccharide levels are not increased.

Figure 5.22

Acquired fibrokeratoma.

Figure 5.23

'Garlic clove' fbrokeratoma.

Surgical treatment is the same as for Koenen's tumours and depends on the size and location of the lesion.

The differential diagnosis of acquired periungual fibroma includes:

• recurring digital fibrous tumours of childhood

• dermatofibrosarcoma

• fibrosarcoma

acrochordon

• cutaneous horn

• eccrine poroma

• pyogenic granuloma

• verruca vulgaris

Subungual filamentous tumour

Subungual filamentous tumours are thread-like, horny, subungual lesions growing with the nail plate and emerging from under the free edge of it. They may cause a longitudinal rim. This entity is probably a narrow, extremely hyperkeratotic fibrokeratoma; it can be pared down painlessly when the nail is cut.

Recurring digital fibrous tumours of childhood (benign juvenile digital fibromatosis)

Recurring digital fibrous tumours are round, smooth, firm tumours with a reddish or livid red colour. They are located on the dorsal and axial surfaces of the fingers and toes, characteristically sparing the thumbs and great toes (Figure 5.24). They may present at birth or develop during infancy, although a single case of presentation in adulthood has been described. There is no sex predominance. Fingers are more often affected than toes. On reaching the nail unit the tumours may elevate the nail plate, leading to dystrophy but not to

Figure 5.24

Benign juvenile digital fibromatosis (Courtesy of C.Moss, UK.)

Figure 5.24

Benign juvenile digital fibromatosis (Courtesy of C.Moss, UK.)

destruction. Often the tumour is multicentric, occurring on several digits. Although an infectious origin is probable, no virus has been isolated and viral particles have not been demonstrated by electron microscopy. Up to 60% recur after excision. Spontaneous regression was noted in 5 out of 61 cases; regression may be hastened by cryosurgery. Radical surgical ablation of the area involved may rarely be necessary, including the nail unit, leading to permanent loss of the nail. Firm plantar nodules may be associated with these tumours.

Histological examination shows a diffuse, proliferative, cellular process in the dermis with increased numbers of apparently normal fibroblasts with uniform, spindle-shaped nuclei. Mitoses are absent or rare. Elastic tissue is decreased. In about 2% of the fibroblasts, paranuclear inclusion bodies, 3-10^m in diameter, can be seen in adequately fixed specimens with the use of stains such as iron haematoxylin, methyl green-pyronin and phosphotungstic acid-haematoxylin. Electron microscopy shows that the inclusions consist of fibrillar masses without a limiting membrane. On the basis of this evidence, it has been suggested that the condition should be termed 'elastodysplasia'.

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