Case Study

Subungual necrosis

A 79-year-old patient with type 2 diabetes of 7 years' duration dropped the family bible on his left great hallux. The toe was exquisitely painful and rapidly developed discolouration beneath the nail plate. After 4 days he visited his general practitioner who diagnosed a subungual haematoma and referred him to the diabetic foot clinic and he was seen the same day (Fig. 2.8a,b). The nail plate was cut back to reveal an area of necrosis involving the nail bed. Differential diagnosis was necrosis caused by infection or purely by hydrostatic pressure from a collection of blood under the nail plate. Systemic antibiotics were prescribed. The necrotic area gradually dried, demarcated and healed. When the new nail plate grew back it was onychogryphotic.

Key points

• It is impossible to assess a nail bed lesion properly without removing the overlying nail plate

• All painful subungual haematomas should be drained without delay by cutting back the nail plate.

Subungual melanoma. Malignant melanoma may also present as a discoloured area under the nail plate. Irregular discolouration of the nail bed and plate and progressive destruction of nail are seen. Some melanomas are not associated with pigment (Fig. 2.9).

Patients should be referred urgently to the dermatologist.

Subungual exostosis. An acutely painful cherry red spot develops under the nail plate. A lateral X-ray reveals bony outgrowth of the distal phalanx. The treatment is surgical.

Fungal infections (tinea pedis)

These can present in several ways:

• Dry, scaly plantar, often in a 'moccasin-like' distribution

• Acute vesicular

• Interdigital, with moist, cracked areas which may be sore, itchy and sometimes malodorous, and are associated with whitish, rubbery, macerated skin, and can undergo erosion.

Fig. 2.10 An area of thickened rubbery white skin between the toes (tinea pedis).

Fig. 2.9 Amelanotic melanoma.

Scrapings can be taken and sent to the laboratory for identification of the infective organism but usually a clinical diagnosis is made.

Treatment of tinea pedis

Canesten spray (clotrimazole 1% in isopropyl alcohol) applied topically is best for interdigital areas. For other parts of the foot Canesten cream can be applied. Treatment should be continued for at least 2 weeks after resolution of symptoms to avoid relapse. Whitfield's ointment is an old-fashioned but useful remedy: different vehicles in the formulation are chosen according to climate and geographical area. Tinactin (tolnaftate) and Mycil (chlor-phenesin) can be bought over the counter in formulations including powder and cream.

Patients with fungal infections should receive precise instructions regarding duration of therapy and preventive measures for the future.

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