Brownish macule on the palm

A 22-year-old female patient presented with a brown colored macule on the left palm of seven weeks duration. The lesion began as a tiny brown macule on the left palm and gradually grew in size over a period of seven weeks. The lesion was asymptomatic. There was no history of vesiculation or scaling of the lesion. She did not give a history of coming in contact with any exogenous chemicals or dyes. The patient was not in the habit of excessively using soap and water to wash her hands. However, the patient gave a history of hyperhidrosis of the palms and soles for the past 2 years. There was no other significant past history. On examination, the patient had a uniformly brown colored macule of about 2× 3 cm on the left palm with irregular margins, distributed on the thenar eminence just above the wrist joint [Figure 1]. The dermatoglyphics were preserved over the macule and there was hyperhidrosis of the palms. The brown macule could not be removed even after rubbing with a cotton ball soaked with alcohol. Scrapings of the macule were mounted on 10% potassium hydroxide (KOH) and observed under the microscope. Brown colored, short, closely septate hyphae along with spores were observed under the microscope [Figure 2]. The classical clinical presentation of brownish macule resembling a stain on the palms along with the observation of brown closely septate hyphae on KOH mount enabled us to make a diagnosis of tinea nigra (TN). However, culture could not be done due to lack of facilities. The patient showed prompt response to topical terbinafine.

Figure 1.

Brown colored macule over the left palm. Note the hyperhidrosis

Figure 2.

Brown colored short, closely septate hyphae (arrow), potassium hydroxide mount ×100

Tinea nigra is a very rare superficial fungal infection caused by a pigmented fungus, Hortaea werneckii, while in some South American countries; it is caused by another species, Stenella araguata. This superficial mycosis is mainly reported from tropical countries, suggesting that hot humid climate favors its growth.[1,2] The predisposing factors for TN have not been clearly elucidated; it is more commonly seen in females, especially housewives who frequently come in contact with soap and water. Hyperhidrosis has been noted as another risk factor as observed in our patient.[2] TN usually presents as a brownish macule on the palms and less frequently on the soles resembling stains caused by silver nitrate. Other sites reported are the face, axilla, and chest. The brown color is due to a melanin like material produced by the fungus. The pigmentation may be more in the periphery than the center. The lesions may be clinically confused with post inflammatory hyperpigmentation, junctional nevi, exogenous stains, melanoma, Addisonian pigmentation and the hyperpigmentation seen in syphilis and pinta. However, KOH mount and fungal culture clinch the diagnosis. KOH mount shows brown short, closely septate hyphae about 5 μm in diameter with branching and budding cells. Culture on Sabouraud's dextrose agar shows brown to black velvety colonies with many aerial hyphae. Skin biopsy may show fungal filaments close to the acrosyringium, indicating that sweat may be a nutrient for this fungus.[3] This benign rare superficial mycosis shows good response to topical terbinafine, ketoconazole, econazole, ciclopirox olamine, benzoic acid ointment, and thiabendazole.[4,5] TN should be considered in the differential diagnosis of pigmented lesions on the palms, since it can mimic several dermatoses.