A case of tinea nigra in children

Abstract

A 6-year-old girl presented with brown patches on her right palm that had persisted for 5 years. Based on clinical manifestations, dermoscopy, and fungal microscopy, the child was diagnosed with tinea nigra. Molecular sequencing confirmed the pathogen as Hortaea werneckii. The patient was successfully treated with the topical application of an antifungal ointment.

A 6-year-old girl presented with a mung bean-sized brown patch on her right palm that had first appeared 5 years prior without any known trigger, associated symptoms, or prior treatment. The lesion gradually deepened and increased in size. The child resided in Tianjin, China, and had no history of trauma, palmar hyperhidrosis, or exposure to subtropical regions. Skin examination revealed irregular brown patches on the right palm with slightly raised margins, well-defined borders, and fine scaling (Fig. 1a). Dermoscopy revealed fine brown strands inconsistent with the dermatoglyphs and no vascular structures (Fig. 1b). Microscopic examination using a 10 % potassium hydroxide (KOH) solution and calcium white fluorescent staining revealed irregularly separated hyphae and oval-shaped microconidia. Fungal culture from dander scrapings incubated on SDA at 26 °C for one week yielded black, shiny yeast-like colonies. Lactophenol cotton blue staining microscopy revealed brown conidia with central segregation (Fig. 2a–d). ITS sequence sequencing (primer ITS4) identified the pathogen as Hortaea werneckii (H. werneckii). The sequence was submitted to GenBank (GenBank accession number PP549966) and showed 99.62 % homology with H. werneckii (GenBank accession number MH063124.1).

Fig. 1.

a: Before treatment; b: Dermoscopy (50X); c: After 2 weeks of treatment.

Fig. 2.

a: 10 % KOH solution (20 μm); b: Calcium white fluorescence staining (20 μm); c: H.werneckii SDA culture; d: Lactophenol cotton blue staining microscopy (20 μm).

The diagnosis of tinea nigra was confirmed. The lesions resolved following two weeks of once-daily topical bifendazole cream application (Fig. 1c). Repeat fungal microscopy was negative.

1. Discussion

Tinea nigra is a superficial fungal disease of the skin that is considered a tropical disease and is usually found in Central and South America, Africa, and Asia [1]. The first case in the Western Hemisphere was described by Cerqueira in Bahia, Brazil, in 1891, while the first report was by Cerqueira Pinto in 1916 [2]. In 1921, Horta first isolated the pathogenic bacterium Cladosporium werneckii, which was later renamed H. werneckii [3]. The clinical manifestations are asymptomatic brown or black scaleless macules, usually on one side, and occasionally involving both [4]. The most common sites are the palms and fingers, but the wrists, plantar, neck, and chest can also be involved [[4], [5], [6], [7]]. Typical dermoscopy shows wispy brown strands or pigmented spicules that do not correspond to dermatoglyphic lines. Additionally, a parallel-ridge appearance, although less frequent, has been described in the literature [8,9]. Typical pathology can be used to identify fungal structures in the stratum corneum. Reflection confocal microscopy allows the visualization of high refractive indices, ramus, and round structures in the stratum corneum, which bear remarkable similarities to filamentous hyphae, isolated fungal components, and conidia [10].

The most common causative pathogen of tinea nigra is H. werneckii; however, Stenella araguata and Curvularia lunata have also been implicated [1,11]. H. werneckii is a lipophilic, keratophilic, biphasic fungus that can attach to the stratum corneum by breaking down its lipids and tolerating high salt and low pH, enabling its survival on human skin. H. werneckii is extremely salt-tolerant (0–30 % [w/v]NaCl), which is why NaCl is often included in culture media. The growth temperature of H. werneckii is up to 37 °C, which explains its colonization in human skin with increased salinity [12]. Known risk factors include trauma, sweaty hands and feet, and exposure to humid or coastal environments [11].

Tinea nigra can be diagnosed based on clinical manifestations and mycological examination, and dermoscopy, reflection confocal microscopy, pathology, and molecular biology can be performed if necessary. Occasionally, it must be differentiated from pigmented nevus, malignant melanoma, palmoplantar lichen planus [13], and post-inflammatory hyperpigmentation. Antifungal drugs and keratolytic agents are typically used for treatment, and have satisfactory efficacy.

CRediT authorship contribution statement

Tengteng Xin: Writing – original draft. Jiahao Li: Data curation. Li Lin: Formal analysis. Yijin Luo: Resources. Wenying Cai: Writing – review & editing. Junmin Zhang: Supervision.

Funding declaration

The authors declare that no funds were received during the preparation of this manuscript.

Declaration of competing interest

All authors declare that they have no conflict of interest.