Superficial fungal infections are some of the most common dermatologic diseases seen worldwide. It is estimated that 13.8~20% of the population has had a dermatophyte infection, and approximately 12~13% has onychomycosis¹. Trichophyton (T.) rubrum, T. tonsurans, T. mentagrophytes, Microsporum (M.) canis are the most common causative agents of superficial fungal infection in the US¹.

Other species, such as Cryptococcus species, can also cause superficial fungal infection¹.

Cryptococcus species are basidiomycetous yeasts that are thought to be the cause of a variety of diseases^2-4. Crypto- coccus (C.) neoformans and C. gattii are the most common pathogenic species^2-4. However, the incidence of infection due to non-neoformans cryptococcal species such as Naganishia (N.) albida and Papiliotrema laurentii (formerly C. laurentii) has increased recently^5,6. Other very rare infections including N. diffluens (formerly C. diffluens) have also been reported (Table 1)⁷ . We present a case of N. diffluen-sinduced superficial fungal infection.

Figure 1. (A, B) Broad annular erythematous scaly patches and plaques on both axilla, back and abdomen (C) A large well-demarcated plaque with inner reticulated patch and nodules

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Figure 2. (A) White and creamy colonies with smooth surfaces developed in Sabouraud dextrose agar at 28℃ for 2 weeks (B) Regular in size and round yeast cells are seen. (Lactophenol cotton blue preparation ×400)

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Figure 3. Alignment of ITS sequences of rRNA gene: Query is the sample from the patient, CBS 160 (GenBank accession number NR111051) is type stain of Naganishia diffluens. The sequences of ITS region of clinical sample were 100% match to that of Naganishia diffluens strain: CBS 160(NR111051.1, type strain), CBS 8985 (KY104323.1), CBS:8990 (KY104324.1).

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A 53-year-old man presented to our clinic with a pruritic skin rash on his trunk and axilla.

For three months, he had mildly pruritic annular, erythematous, scaly patches with inner small, crusted papules and nodules on both axilla and trunk (Fig. 1). The lesions enlarged after the application of topical corticosteroids, administered by a local medical center approximately 2 months ago. Additionally, he suffered from hypertension and alcoholic liver cirrhosis. The patient had recurrent ascites and a history of being hospitalized in a bed-ridden state regularly. Furthermore, because of his low socio-economic status, his surroundings were unclean and humid.

A potassium hydroxide test performed on the scales on the lesions of multiple sites was all positive, and multiple round yeast cells were observed. Specimens were collected at least twice from multiple lesions and cultured at 28℃ for two weeks on Sabouraud dextrose agar. All of the agars produced white and creamy colonies with smooth surfaces (Fig. 2A). Lactophenol cotton blue staining of the smears showed yeast cells similar to Cryptococcus under the micro- scope (Fig. 2B). The presence of N. diffluens was finally confirmed through sequencing of the rRNA gene' internal transcribed spacer (ITS) (Fig. 3). Furthermore, no evidence of systemic infection was discovered in X-ray, CT, or laboratory findings. Thus, we diagnosed the patient with a superficial fungal infection caused by N. diffluens. For two weeks, the patient was treated with an oral antifungal agent (itracona- zole, 100 mg) and a topical antifungal agent (isoconazole), and the lesions significantly improved. There was no evidence of recurrence for 6 months.

Most rare Cryptococcus species belong to the C. albidus clade (N. adeliensis, N. diffluens, N. liquefaciens, Filobasidium magnus, and N. uzbekitanensis). They were misidentified as N. albida before molecular identification (formerly C. albidus). The ITS region and the 28S D1/D2 region of rRNA DNA sequence analysis reclassified them as N. diffluens⁸.

The genus Naganishia has asexually reproducing yeast species. Naganishia species are basidiomycetous yeasts and are characterized by the lack of basidiocarps. Typically, hyphae and pseudohyphae are absent, while budding cells and ballistoconidia are present⁹. N. diffluens are globose or elliptical, encapsulated yeast cells of varying sizes⁸. The histopathological features of N. diffluens are similar to those of cryptococcal infection, and a phenol oxidase test that is negative can aid in the differentiation from C. neoformans, the most common cause of cryptococcosis. Biopsy, culture, and molecular analysis are required for a definitive diagnosis. For accurate identifi- cation of N. diffluens isolates, DNA sequence analysis of the ITS region and the 28S D1/D2 region of rRNA are necessary7.

Typically, primary cutaneous infections caused by Crypto- coccus species occur infrequently as a result of organisms being directly inoculated into the skin by a parasitized object. The disease's clinical manifestation is determined by the host's response, the size of the inoculum, and the organism's innate virulence. Cryptococcosis can present with a variety of skin and soft tissue manifestations including purpura, vesicles, nodules, abscesses, ulcers, acneiform eruptions, granulomas, pustules, draining sinuses, and cellulitis^10,11. The majority of skin and soft tissue manifestations occur in the context of a disseminated disease, which is seen in 10~15% of patients with systemic cryptococcosis¹¹. The symptoms of systemic cryptococcosis can range from a mild fever and cough to meningitis, osteomyelitis, pyelonephritis, prostatitis, hepatitis, and peritonitis¹⁰. Thus far, most of the reported cases have been by C. neoformans. Subcutaneous cryptococcosis due to N. diffluens (formerly C. diffluens) was first reported in Turkey (Table 1)7. In that case, the patient has a two-month history of nontender nodules that began on the right wrist and progressed to the right arm. The patient was treated through oral itraconazole for 3 months after diagnosis through culture, biopsy, and DNA sequence analysis. In addition to N. diffluens, the first case of N. albida superficial infection was reported in Iran¹². In that case, the patient has been suffering from a hyperpigmented patch on his axilla for more than a month. The patient was treated through oral itraconazole for 10 days after diagnosis through culture and DNA sequence analysis. The case described here is the first report of a superficial infection caused by N. diffluens in South Korea. The patient's alcoholic liver cirrhosis and long-term bed-ridden condition as a result of cirrhosis compli- cations are thought to be risk factors for the superficial fungal infection.

The first choice of treatment for cryptococcosis is the combination of amphotericin B and flucytosine^13,14. However, the treatment of N. diffluens superficial infection is not well defined. Oral itraconazole was used successfully in reported cases, including this one7, and in vitro susceptibilities of N. diffluens to several antifungal agents (amphotericin B, flu- cytosine, fluconazole, itraconazole, voriconazole, and posa- conazole) revealed that voriconazole and posaconazole have good activity against N. diffluens¹⁵.

Unfortunately, the biopsy was not performed in this case. However, it is of diagnostic significance in that the test (including KOH, culture, molecular analysis) conducted on the multiple sites of lesion produced the same results. The ability of N. diffluens to cause superficial infection has been discovered through this report and literature reviews. As a result, we present a rare case of N. diffluens caused superficial fungal infection.