The portal of entry for the organisms concerned, usually staphylococci, is a break in the skin or cuticle as a result of minor trauma. The subsequ-ent acute inflammation, often with the formation of pus in the nail fold or under the nail, requires systemic treatment with flucloxacillin or erythro-mycin and appropriate surgical drainage.
A combination of circumstances can allow a mixture of opportunistic pathogens (yeasts, Gram-positive cocci and Gram-negative rods) to colonize the space between the nail fold and nail plate. Predisposing fac-tors include a poor peripheral circulation, wet work, working with flour, diabetes, vaginal candidosis and overvigorous cutting back of the cuticles.
The nail folds become tender and swollen (Figs 13.26 and 13.28) and small amounts of pus are discharged at intervals. The cuticular seal is damaged and the adjacent nail plate becomes ridged and discoloured. The condition may last for years.
In atypical cases, consider the outside chance of an amelanotic melanoma. Paronychia should not be con-fused with a dermatophyte infection in which the nail folds are not primarily affected.
Test the urine for sugar, check for vaginal candidosis.
Pus should be cultured.
Manicuring of the cuticle should cease. The hands should be kept as warm and as dry as possible, and the damaged nail folds packed several times a day with an imidazole cream. If there is no response, and swabs confirm that candida is present, a 2-week course of itraconazole should be considered.
The common dermatophytes that cause tinea pedis can also invade the nails.
Toenail infection is common and associated with tinea pedis. The early changes occur at the free edge of the nail and spread proximally. The nail plate becomes yellow, crumbly and thickened. Usually only a few nails are infected but occasionally all are. The fingernails are involved less often and the changes, in contrast to those of psoriasis, are usually confined to one hand.
The condition seldom clears spontaneously.
Psoriasis has been mentioned. Yeast infections of the nail plate, much more rare than dermatophyte infec-tions, can look similar. Coexisting tinea pedis favours dermatophyte infection of the nail.
Microscopic examination of a nail clipping is a simple procedure. Cultures should be carried out in a mycology laboratory.
Remember that most symptom-free fungal infections of the toenails need no treatment at all.
Peri-ungual warts are common and stubborn. Cryo-therapy must be used carefully to avoid damage to the nail matrix. It is painful but effective.
Peri-ungual fibromas (see Fig. 21.5) arise from thenail folds, usually in late childhood, in patients with tuberous sclerosis.
Glomus tumours can occur beneath the nail plate.The small red or bluish lesions are exquisitely painful if touched and when the temperature changes. Treat-ment is surgical.
Subungual exostoses (Fig. 13.22) protrude painfullyunder the nail plate. Usually secondary to trauma to the terminal phalanx, the bony abnormality can be seen on X-ray and treatment is surgical.
Myxoid cysts (Fig. 13.29) occur on the proximalnail folds, usually of the fingers. The smooth domed swelling contains a clear jelly-like material that tran-silluminates well. A groove may form on the adjacent nail plate. Cryotherapy, injections of triamcinolone and surgical excision all have their advocates.
Malignant melanoma should be suspected in any subungual pigmented lesion, particularly if the pigment spreads to the surrounding skin. Subungual haematomas may cause confusion but ‘grow out’ with the nail (Fig. 13.21). The risk of misdiagnosis is high-est with an amelanotic melanoma, which may mimic chronic paronychia or a pyogenic granuloma.