Tinea nigra

Description:

A superficial fungal infection of skin characterised by brown to black macules which usually occur on the palmar aspects of hands and occasionally the plantar and other surfaces of the skin. World-wide distribution, but more common in tropical regions of Central and South America, Africa, South-East Asia and Australia. The aetiological agent is Hortaea (Phaeoannellomyces) werneckii a common saprophytic fungus believed to occur in soil, compost, humus and on wood in humid tropical and sub-tropical regions.

Clinical manifestations:

Skin lesions are characterised by brown to black macules which usually occur on the palmar aspects of hands and occasionally the plantar and other surfaces of the skin. Lesions are non-inflammatory and non-scaling. Familial spread of infection has also been reported.

Typical brown to black, non-scaling macules on the palmar aspect of the hands. Note there is no inflammatory reaction.

Laboratory diagnosis:

1. Clinical Material: Skin scrapings.

2. Direct Microscopy: Skin scrapings should be examined using 10% KOH and Parker ink or calcofluor white mounts.

Skin scrapings mounted in 10% KOH showing pigmented brown to dark olivaceous (dematiaceous) septate hyphal elements and 2-celled yeast cells producing annelloconidia typical of Hortaea werneckii.

3. Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar.

4. Serology: Not required for diagnosis.

5. Identification: Characteristic clinical, microscopic and culture features.

Causative agents:

Hortaea werneckii (syn. Phaeoannellomyces werneckii).

Management:

Usually, topical treatment with Whitfield's ointment (benzoic acid compound) or an imidazole agent twice a day for 3-4 weeks is effective.

Further reading:

Ajello L and R.J. Hay. 1997. Medical Mycology Vol 4 Topley & Wilson's Microbiology and Infectious Infections. 9th Edition, Arnold London.

Elewski BE. 1992. Cutaneous fungal infections. Topics in dermatology. Igaku-Shoin, New York and Tokyo.

Kwon-Chung KJ and JE Bennett 1992. Medical Mycology Lea & Febiger.

Richardson MD and DW Warnock. 1993. Fungal Infection: Diagnosis and Management. Blackwell Scientific Publications, London.

Rippon JW. 1988. Medical Mycology WB Saunders Co.