Pigmented Macular Lesion on Hand


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An 8-year-old boy presents with a 2-month history of an asymptomatic rash on the dorsum of his right hand. He and his family have recently moved from a coastal region in Mexico. Medical and family history are otherwise unremarkable. On examination, he has a 2-cm pigmented macular lesion with an irregular outline centrally located on the dorsal aspect of his right hand. The remainder of the physical examination is normal. Dermoscopy rules out a nevoid lesion, and septated filaments are observed on potassium hydroxide (KOH) test.

Tinea nigra is an uncommon superficial fungal infection. It is strictly limited to the stratum corneum and is caused by dematiaceous fungi. The characteristic causative organism of tinea nigra is Hortaea werneckii, a fungus that grows as a black yeast...

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Tinea nigra is an uncommon superficial fungal infection. It is strictly limited to the stratum corneum and is caused by dematiaceous fungi. The characteristic causative organism of tinea nigra is Hortaea werneckii, a fungus that grows as a black yeast and can transform into a mold.1,2 The fungus is halophilic and favors hypersaline environments up to 30% NaCl, such as coastal regions.3Other fungi that have been considered to cause tinea nigra are Cladosporium castellanii, Cladophialophora saturnica, and Phoma hibernica.4-7

The condition was first described in 1973 in Venezuela.4 Although tinea nigra is generally not associated with other manifestations in the body, H werneckii was reportedly isolated from a splenic abscess in 2 patients in 2005.8

Most cases of tinea nigra have been reported in Latin America, Asia, Africa, and the Pacific Islands.2,9-13 Tinea nigra has less commonly been reported in Europe and the United States.2 The condition is seen in young women and men with no gender predilection, and it is more commonly seen in children and adolescents.

The most important predisposing factor for tinea nigra is hyperhidrosis, and it is most commonly found in the palmoplantar regions of the body.2 Initially, the organism most likely attaches to its host through minor trauma. The incubation time of H werneckii is unknown but may vary from weeks to years.12 It is seen less commonly on the arms, legs, neck, trunk, and dorsal aspects of the hands.1,2,9,10,14

Typically, tinea nigra is unilateral and appears as a brown to gray macule or plaque that is hyperpigmented and circumscribed. The lesion can become darker at the borders with an irregular outline. Some patients have observed that the macules change color throughout the day.2 Lesions can also be covered with fine scales. 1,2,9,10,13 When untreated, tinea nigra is a chronic skin condition. Patients are typically asymptomatic, but occasionally patients report pruritus.1,2

Diagnosis of tinea nigra is based on clinical physical findings and confirmed with a laboratory diagnosis of fungal infection. This can be performed by direct mycological examination with 10% to 20% KOH preparation. KOH prep testing of the affected skin scraping reveals dematiaceous, septate hyphae with colors that vary from brown to black on microscopic examination.1,2,9,10,15 Dermoscopy is also useful for distinguishing tinea nigra from a melanocytic lesion. Tinea nigra will show a nonmelanocytic-pattern macule with superficial brown pigmentation in specks. Seeing the characteristic fungal growth pattern can help differentiate the infection from nevi, particularly melanoma.1

Culturing of the affected skin on Sabouraud glucose agar with or without antibiotics, incubated at 28°C, usually reveals fungal growth within 5 to 6 days.1 The fungus grows in 2 phases: the initial yeast-like phase shows smooth colonies that can be creamy in appearance and dark green to black in color, and the mold phase shows fungus as filaments with wooly or smooth appearance and filamentous hyphae.1

The differential diagnosis for tinea nigra should include other causes of pigmented skin lesions such as melanocytic nevi, lentigines, palmar lichen planus, fixed drug eruptions, and melanoma.16,17 These can be distinguished from tinea nigra by fungal culture, KOH prep, or skin biopsy. Light brown, wavy, and thick hyphae with occasional dark hyphae differentiate tinea nigra from other fungal infections, particularly those caused by conidia, which appear more uniformly heavily pigmented.2 On hematoxylin and eosin stain, hyphae and spores are seen at the stratum corneum.1 Due to the irregular borders, pigmentation, and growth of the lesion, tinea nigra may be mistaken for melanoma.13 Therefore, an accurate diagnosis is important in order to prevent unnecessary diagnostic and excisional surgery as well as scarring.

Treatment of tinea nigra includes topical therapies, which have been found to be rapidly effective. Common topical antifungals include bifonazole, clotrimazole, ketoconazole, terbinafine, and ciclopirox olamine gel.2,18-21 Oral itraconazole was first reported to be effective in a case correspondence.22 A topical keratolytic agent such as 3% salicylic acid or Whitfield ointment (6% benzoic acid and 3% salicylic acid) may also be beneficial.2 Oral griseofulvin has not been found to be effective.1 Effectiveness of therapy is based on clinical experience and case reports; no randomized controlled clinical trials have evaluated treatments for tinea nigra. Overall, tinea nigra is found to clear quickly and effectively with these treatments.

The patient in this case was prescribed topical ketoconazole cream for 4 weeks, and the lesion regressed.

Yasmin Khalfe, BA, and Emily Burns, BA, are medical students at Baylor College of Medicine, and Christopher Rizk, MD, is a dermatologist at Elite Dermatology in Houston, Texas.


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