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Dermatophytosis And Other Sup... Health Article

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Infections

Infections caused by the pigmented fungus S. dimidiatum ( Hendersonula toruloidea ) closely resemble dry-type dermatophytosis caused by T. rubrum. S. dimidiatum was originally described as a plant pathogen, but it appears to be a genuine cause of human infection. A similar type of infection has been ascribed to a nonpigmented mold, S. hyalinum. In both cases the affected patients have originated from the tropics.

The precise mechanisms of infection with either organism are unknown. S. hyalinum has never been isolated from the environment, and although S. dimidiatum is a pathogen of certain plants such as fruit trees, patients do not usually give a specific history of exposure. It has been found that healthy individuals in some tropical areas carry these organisms on the feet but do not have overt disease, suggesting that asymptomatic carriage may be followed under the appropriate conditions by infection. Infections have been described in immigrants from tropical areas to the United Kingdom, Canada, and France. Patients have also been identified in the southern United States, Trinidad, Colombia, Ecuador, and India, and it is likely that the infection is more widespread. Occasionally, it may be seen in patients who have paid short visits to the tropics.

Clinical Features

The clinical signs of skin infection with both Scytalidium species are identical to those associated with dry-type T. rubrum infections. ⁴⁴ There is scaling of the lateral interdigital spaces, over the soles, and on one or both palms. Itching is usually minimal. Onychomycosis may also develop. Often there is early invasion of the lateral border of the nail without significant thickening of the nail plate (Fig. 265-6) , but eventually the whole nail plate may be undermined and onycholysis may lead to shedding of the complete nail. Hyperpigmented streaks may occur in the nails, although these are not pathognomonic for these infections and can be seen with other forms of inflammatory nail dystrophy.

Diagnosis

Scrapings or nail clippings examined after treatment with potassium hydroxide contain sinuous fungal hyphae. On close inspection the morphology is different from that normally seen with dermatophyte hyphae, but accurate discrimination requires experience. Both organisms grow on Sabourauds agar but are inhibited if cycloheximide (Acti-Dione) is incorporated in the medium.

Treatment

There is no satisfactory therapy for either infection. Whitfields ointment may be used to treat Scytalidium infections of the sole or the palm. However, none of the specific antifungal drugs currently available produces consistent results.

Other Forms Of Onychomycosis

A number of other fungi may cause onychomycosis. The most common of these is Scopulariopsis brevicaulis, which usually causes infection of the great toenails. Some patients with this form of infection have previously abnormal toenails (e.g., onychogryphosis). Scopulariopsis infections of the nails have a typical cinnamon color that is caused by the presence of fungal spores seen on direct microscopy of the nail. The fungus is easy to isolate in culture. Treatment may be difficult, but chemical nail removal with 40 urea may be useful.

Superficial white onychomycosis may be caused by Acremonium or Fusarium species. These infections are similar to those caused by T. mentagrophytes, and the identity of the causative organisms should be confirmed by culture.

Occasionally, other fungi are isolated from nail material. In many cases they appear to be colonizing the undersurface of dystrophic nail plate. On rare occasions, however, they may contribute to the nail pathology by invasion. This is best established by repeated attempts at culture, and if the organism is isolated on numerous occasions and if hyphae are present in the nail, it is likely that the organism is implicated in the nail disease. Examples of infections caused by a range of different organisms, such as Aspergillus, Fusarium, and Acremonium spp., have been recorded. Fusarium is now known to cause a range of fungal nail infections from superficial white onychomycosis to proximal subungual disease; in severely neutropenic patients nail infection may be followed by systemic dissemination. There is seldom effective oral therapy for these infections, ⁴⁵ and nail removal with 40 urea is probably the best alternative treatment.