Are You Confident of the Diagnosis?

What you should be alert for in the history

There is a history of a stable or slowly growing single light-to-dark-brown macule, patch, or linear lesion on the palm or sole; rarely, there can be multiple lesions or lesions on the trunk. There may be a history of a preceding injury; contact exposure to wood, sewage, or compost; or a history of hyperhidrosis. Patients who do not live in a humid environment may give a history of travel to a tropical locale.

Characteristic findings on physical examination

The patch may range in shape from round to geometric, and is asymptomatic or occasionally pruritic (Figure 1).

Figure 1.

Clinical image of tinea nigra on the palm of a light skinned person. (Courtesy of Francisco Bravo, MD)

Expected results of diagnostic studies

Dermoscopy of the lesion will reveal pigment that does not follow dermatoglyphs (Figure 2), scraping of the lesion with a No. 15 blade may remove portions of the lesion, and microscopic examination of the scrapings treated with 20% potassium hydroxide (KOH) will reveal pigmented branching hyphae and round spores.

Figure 2.

Dermatoscopic appearance of tinea nigra on the palm of a light skinned person. (Courtesy of Francisco Bravo, MD)

Histopathology is rarely necessary, but biopsy with H&E staining may have acanthosis, hyperkeratosis, and a mild perivascular infiltrate; the periodic acid Schiff (PAS) stain will show hyphae in the stratum corneum (Figure 3).

Figure 3.

Tinea nigra, H&E staining, original magnification x10.

Culture of skin scrapings or tissue on Saboraud at 25^oC will grow mucoid black colonies at one week. PCR testing for the most common cause of tinea nigra, Hortaea werneckii, is available.

Diagnosis confirmation

The most common differential diagnosis for tinea nigra is a melanocytic lesion (an acral lentiginous melanoma, junctional nevus, or lentigo). These entities can be differentiated from tinea nigra by dermoscopy, or by exam of scrapings of the lesion using KOH.

Skin staining with silver nitrate, postinflammatory hyperpigmentation, secondary syphilis, and Addison’s disease are also in the differential diagnosis, but should be able to be excluded by history, additional findings on physical exam, or by KOH exam.

Who is at Risk for Developing this Disease?

Otherwise healthy young men, women, and children who live in humid tropical environments are most at risk for developing tinea nigra. Hyperhidrosis of the palms or soles and exposure to soil, sewage, and compost are also frequently associated risk factors.

What is the Cause of the Disease?

Etiology

Hortaea werneckii is a dematiaceous yeast that causes most cases of tinea nigra. It was formerly classified as Cladosporium werneckii, Exophalia werneckii, and Phaeoannellomyces werneckii. Less commonly, tinea nigra has been reported to be caused by another dematiaceous yeast, Stenella araguata.

Pathophysiology

The pigmented yeast lives in compost, soil, and trash, and traumatic inoculation of the fungus into the skin results in infection. The fungus is lipophilic and thrives in high salinity, thus it has an affinity for areas of the skin with high concentrations of eccrine glands. The infection is limited to the stratum corneum, where the fungus survives by digesting the lipids.

Systemic Implications and Complications

Tinea nigra in healthy patients is always a superficial infection limited to the stratum corneum. Very rarely, in severely immunosuppressed patients, specifically patients with neutropenia following treatment for acute leukemia, Hortaea werneckii has been isolated from blood cultures or internal organ abscesses. Cases of systemic infection with dematiaceous fungus are referred to as phaeohyphomycoses.

Treatment Options

Topical therapy

Generally, tinea nigra can be treated topically. In limited cases, the pigmented patch may be scraped off with a No. 15 scalpel or with repeated epidermal striping with adhesive tape given that it is confined to the stratum corneum.

Keratolytics, including salicylic acid, urea, and combinations of salicyclic acid and benzoic acid known as Whitfield’s ointment, have been reported to be effective.

Topical antifungals, including the imidazoles clotrimazole, ketoconazole, and miconazole, have all been reported to be effective when used for 2-4 weeks. Ciclopiroxolamine, terbinafine, and naftifine are also reported to be effective.

Oral Therapy

Oral griseofulvin has been reported to be ineffective, and generally oral therapy is neither necessary nor has it been reported to be effective.

Optimal Therapeutic Approach for this Disease

For small lesions, removal with a No. 15 blade or tape stripping may be the most direct approach. This may be a better approach than topical therapy in children who are likely to put their hands in their mouths.

Keratolytics and topical antifungals in gel or spray form may be better tolerated on the palms than creams.

If a patient gives a history of hyperhidrosis, drying agents such as aluminum chloride should be used in conjunction with antifungals or keratolytics.

Patient Management

Topical treatment has been effective in all reported cases. Treatment should be effective within 4 weeks, and if it is not, the diagnosis should be re-evaluated. Recurrence is rare.

Unusual Clinical Scenarios to Consider in Patient Management

Generally, topical therapy is successful and lesions do not recur. Pediatric patients can be managed in a way similar to adult patients.