Table 42 Causes and associations of nail shedding

Local inflammation, e.g. acute paronychia (Figures 4.7-4.12) Kawasaki's syndrome Fever or systemic upsets Syphilis

Bullous dermatoses, e.g. pemphigus Stevens-Johnson syndrome

Toxic epidermal necrolysis (Lyell's syndrome) (Figures 4.7-4.9) Drugs

Cytotoxics Antibiotics Retinoids Keratosis punctata Local trauma X-irradiation

Acrodermatitis enteropathica

Hypoparathyroidism with amelogenesis imperfecta

Yellow nail syndrome_

HYPERTROPHIC NAIL AND SUBUNGUAL HYPERKERATOSIS

Ideally, the term 'hypertrophy of the nail plate' should be restricted to conditions causing nail enlargement and thickening by their effects on the nail matrix (excluding nail bed and hyponychium). The term 'subungual hyperkeratosis' should relate to those entities leading to thickening beneath the preformed nail plate: that is, thickening of the nail bed or hyponychium (Figure 4.13). In practice, this differentiation is difficult to define and mixed cases are commonly seen, for example in psoriasis (Figures 4.14, 4.15).

The normal thickness of finger nails is approximately 0.5 mm; this is consistently increased in manual workers and in many

Severe Toe Nail Psoriasis

Figure 4.13

Cryptogenic hyperkeratosis.

disease states such as congenital ichthyoses, Darier's disease, psoriasis and repeated trauma. The latter particularly relates to toe nails where microtrauma and footwear are constantly affecting the nails.

Onychogryphosis (Figures 4.16-4.18), a condition mainly seen in the great toe nails of elderly and infirm individuals, is probably due to trauma, footwear pressure, neglect and sometimes associated poor peripheral circulation and fungal infection; these and less common causes are listed in Table 4.3.

If the nail bed is left continuously exposed by nail removal or disease for more than a few months irregular hyperketosis and failure of nail plate adhesion may ensue

Subungual Hyperkeratosis

Figure 4.14

Subungual hyperkeratosis due to psoriasis.

Figure 4.14

Subungual hyperkeratosis due to psoriasis.

Subungual Hyperkeratosis Causes

Figure 4.15

Distal subungual hyperkeratosis in psoriasis; note proximal inflammatory brown margin.

Figure 4.15

Distal subungual hyperkeratosis in psoriasis; note proximal inflammatory brown margin.

Figure 4.16

Oyster-like onychogryphosis.

Figure 4.17

Onychogryphosis—ram's horn deformity.

Epithelial hyperplasia of the subungual tissues results from repeated trauma and exudative skin diseases and may occur with any chronic inflam-matory condition involving this area. It is especially common in psoriasis, pityriasis rubra pilaris and chronic eczema and may also be due to fungi (Figures 4.19-4.25). Histological investigation reveals periodic acid-Schiff reagent (PAS)

Onychogryphosis

Figure 4.18

Severe onychogryphosis.

Figure 4.18

Severe onychogryphosis.

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