Tinea nigra - Skin in Adult
After contamination from an infected source (eg, soil, sand, waste, or wood), the mycosis infects the stratum corneum, resulting in a dark-colored macule caused by the accumulation of a melanin-like substance in the fungus. The fungus adheres to the skin because of its ability to survive high-salinity environments. The incubation period is typically 2 to 7 weeks; however, a study has shown the incubation period to range from a few weeks to 20 years.
Tinea nigra is an uncommon finding in the US, with most cases found near coastal areas or in the southern US. It is more commonly found in tropical regions of Central and South America, Africa, Southeast Asia, and Australia. The most affected populations are children and adolescents (children are more prone to exposure to the fungus); however, persons of any age may be affected. There is a female-to-male incidence of 3:1. Tinea nigra seems to appear less often in patients with more deeply pigmented skin; however, this may be due to reduced recognition of the disease. Risk factors include living in or travel to tropical areas where the organism is common. Risk is increased in patients with excessive sweating.
Signs – Usually asymptomatic, well-demarcated lesion of variable size and irregular shape (between 1 and 5 cm). There is often a single brown or black macule on the palmar or plantar skin, although there may be multiple spots; it occurs rarely on the neck or trunk. The lesion may rarely appear scaly. Many times the lesion is misdiagnosed as malignant melanoma.
Symptoms – Tinea nigra usually lacks erythema or induration and is rarely pruritic. It is usually a benign condition that clears within 2 weeks of treatment with an antifungal agent and rarely reoccurs.
Immunocompromised Patient Considerations
The fungi involved in causing infections of tinea nigra can lead to serious infections in immunocompromised patients. There is a risk of disseminated disease from superficial cutaneous fungal infections noted in transplant patients.
B36.1 – Tinea nigra
186289000 – Tinea nigra
- Trauma resulting in superficial hemorrhage
- Melanoma – Presents with irregular borders, color of different shades, expanding diameter; easily differentiated from tinea nigra using dermatoscopy. No hyphae found on KOH scrapings.
- Junctional nevus – Mole found on the border of epidermis and dermis; no hyphae found on KOH scrapings.
- Addisonian pigmentation – Increased pigmentation resulting from increased levels of the pituitary hormones MSH and ACTH in Addison's disease. Pigmentation usually occurs on the mucosa, elbows, knees, and dorsa rather than the plantar surface of hands.
- Post-inflammatory pigmentation – Sequelae of inflammatory skin condition; evidence of inflammatory condition prior to hyperpigmentation.
- Palmar rash of syphilis – Secondary syphilis causes erythematous papulosquamous eruption and weeping or crusted lesions on palms; also presents with regional lymphadenopathy (70%). Diagnosis by dark-field microscopy or serologic testing (VDRL, RPR).