Once specimens are received in the laboratory, microscopy is performed. An interim report is then released. Specimens are then set up on specialised agar containing antibiotics and cycloheximide to inhibit the growth of bacteria and saprophytic fungi. Cultures are incubated at 28°C for three weeks. If microscopy is positive (M+) and no pathogen (C-) has grown in the interim, specimens are held an extra week. Infrequently, where microscopy and culture of nail scrapings is negative and the diagnosis is still suspected, nails can be examined for fungal elements using special stains.

Results:

Specimen types have been subdivided into three anatomical categories (nails, hair and skin) based broadly on the three clinical presentations of onychomycosis, tinea capitis, and tinea corporis/ cruris/pedis. Onychomycosis refers to fungal infections of the nails and includes tinea unguium caused by dermatophytes but also non-dermatophyte fungi and yeasts, predominantly Candida spp.

Negative laboratory report:

A common reason for negative microscopy and /or culture is an incorrect clinical diagnosis. More than 50% of dystrophic nails do not have a fungal cause, so it is important to establish a correct laboratory diagnosis before treating a patient with an antifungal agent. Other reasons for false negative results include sampling variation associated with an inadequate specimen and/or splitting the sample to perform microscopy and culture; the presence of nonviable hyphae in the distal portion of the nail; uneven colonisation of the nail by fungus; and overgrowth by contaminant saprophytic fungi. Careful re-collection to obtain sufficient material may be necessary to confirm negative results.

Nails:

The analysis of nail specimens from the hands and feet. Fingernails: Of 1202 specimens processed, 59% were negative by both microscopy and culture; 11% had hyphae seen on microscopy but were negative by culture; 27% of all finger and thumbnail cultures grew a yeast, predominantly Candida albicans (88% of all positive nail/hand cultures). Only 3% of all fingernail specimens grew a dermatophyte.

Toenails:

57% of 5097 toenail cultures were negative by both microscopy and culture. 22% were positive by microscopy but culture negative for reasons stated previously. As the literature would suggest, yeast infection of toenails is rare. Dermatophytes (20%) predominate as the main cause of onychomycosis of the lower limbs. Transmission of these dermatophytes is usually via the feet and toe web spaces, which are the major reservoir on the human body. Onychomycosis can be regarded as the end stage of tinea pedis. Desquamated skin scales containing hyphae are shed and survive for months to years on floors and carpets. Infrequently non-dermatophyte moulds are implicated in toenail infections such as Aspergillus. There is some uncertainty as to the significance of these cultures, and repeat culture may be indicated.

Treatment options:

With tinea unguium, topical treatment is successful only with surgical removal of the nail combined with oral therapy. First-line treatment for all types of nail tinea consists of: 1. terbinafine (child < 20 kg: 62.5 mg; 20 to 40 kg: 125 mg) 250 mg orally, daily for six weeks for fingernails and 12 weeks for toenails or (if terbinafine is not tolerated) 2. itraconazole 200 mg orally, twice daily for seven days every month for 2-4 months or 3. fluconazole 150 to 450 mg orally, once weekly for 12 to 52 weeks. Successful management of candidiasis of the nail requires removal of risk factors e.g. water immersion.

Tinea capitis:

Of 414 hair samples submitted over this period, 329 (80%) were negative by both microscopy and culture. Dermatophytes isolated include M. canis (46%); T. tonsurans (42%); M. gypseum (5%); T. mentagrophytes (5%) and T. rubrum (2.5%). This condition afflicts predominantly prepubertal children. Clinically it can present as alopecia or a more inflammatory lesion (kerion). It is noteworthy that T. tonsurans, an anthropophilic fungus, is emerging as a common cause of tinea capitis in children and spreads easily from child to child.

Treatment options:

Tinea capitis often requires oral therapy to eradicate the infection. Treatment options include 1. griseofulvin fine particle (child: 20 mg/kg up to) 500 mg orally, daily for 4-8 weeks, or 2. terbinafine (child< 20 kg: 62.5 mg; 20 to 40 kg: 125 mg) 250 mg orally, daily for four weeks.

Tinea corporis/cruris/pedis:

Of the 7406 specimens received from skin sites, 73% were both microscopy and culture negative; 5% were positive only by microscopy. Of the 22% culture positive specimens, 19% grew a dermatophyte and 3% a yeast.

Treatment options:

When topical treatments have failed, recommended oral therapy includes: 1. griseofulvin fine particle (child: 10 to 20 mg/kg up to) 500 mg orally, daily for at least four weeks or 2. terbinafine (child <20 kg: 62.5 mg; 20 to 40 kg: 125mg) 250 mg orally, daily for at least two weeks, depending on the response or 3. itraconazole capsules 200 mg orally, twice daily for one week for tinea of the feet or hands or 4. itraconazole capsules 200 mg orally, once daily for one week for tinea elsewhere.

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General Practice Pathology is a new regular column each authored by an Australian expert pathologist on a topic of particular relevance and interest to practising GPs. The authors provide this editorial, free of charge as part of an educational initiative developed and coordinated by Sonic Pathology.