Fusarium species are molds that are widely distributed throughout the environment, including soil, air, water, and plants_1-3. They generally infect immunocompromised patients, especially those with hematologic malignancy, bone marrow transplantation, and neutropenia_2,3. They rarely cause local infections, like septic arthritis, endophthalmitis, osteomyelitis, cystitis, and brain abscess, in immunocompetent patients₂. However, they can cause cutaneous infections through skin breakdown by burns, trauma, foreign bodies, or vascular insufficiency_2,3.

The patient provided written informed consent. The patient was a 64-year-old male presented with a tender, erythematous, deep-seated nodule on the outer aspect above his left ankle. This nodule developed one month after an intralesional triamcinolone injection for lipoma was administered at a private clinic (Fig. 1A, 1B). His vital signs were normal. He had no symptoms except for tenderness above his left ankle. He had no history of skin infection by Fusarium. Laboratory investigations showed that his complete blood cell count, liver function test, and renal function test reports were within the normal range. A skin biopsy was taken from the tender nodule and was stained with Gomori methenamine silver (GMS) stain. Additionally, fungal culture of the skin tissue sample was done on Sabouraud dextrose agar (SDA) plate. Histopathological examination showed dense mixed inflam- matory cells and red blood cell extravasation in deep dermis. Fungal hyphae were observed in subcutaneous tissue stained with GMS stain (Fig. 2). The top view of the colonies obtained on the SDA plate appreared yellow in the center and had white floccose appearance (Fig. 3A). The bottom view of the SDA plate showed yellow-brownish colored colonies (Fig. 3B). Lactophenol cotton blue staining of the culture revealed sickle-shaped macroconidia with three thick septa (Fig. 3C). 28S rRNA sequencing was performed to confirm the fungal species, and the fungal culture was identified as Fusarium solani (Fig. 4). Based on these findings, cutaneous fungal infection by F. solani was diagnosed. The patient was treated with oral itraconazole (200 mg/day) for about 4 months and was completely cured. The patient was followed up for 12 months and showed no clinical signs of recurrence (Fig. 1C).

Figure 1. (A-B) Tender, erythematous, deep-seated nodule on the outer aspect above the left ankle (C) The fungal infection was cured and did not relapse during the 12-month follow-up period.

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Figure 2. (A) Mixed dense inflammatory cells and red blood cell extravasation in the deep dermis (H&E, ×200) (B) Fungal hyphae were observed in the subcutaneous tissue (Gomori methenamine silver stain, ×400).

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Figure 3. (A) Top view of the Sabouraud dextrose agar plate showed a white floccose colony. (B) Bottom view of the colony showing yellowish to brownish color (C) Sickle-shaped macroconidia with three thick septa were observed (lactophenol cotton blue stain, ×400).

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Figure 4. RNA sequence alignment of the sample from the patient was 100% identical to the 28S rRNA of Fusarium solani (GenBank accession number KT313637.1).

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Fusarium species are widely distributed throughout the environment. They are divided into several species complexes (SC) such as F. solani SC, F. oxysporum SC, F. fujikuroi SC, and F. dimerum SC4. Fusarium infection has rarely been reported in immunocompetent individuals. It shows slower progression in such patients than in immunocompromised patients₅. Usually, patients with Fusarium infection have a previous history of infection through skin breakdown₅. In this case, cutaneous infection occurred one month after intralesional triamcinolone injection. Therefore, cutaneous fungal infection should be considered even in healthy patients showing slowly progressing skin lesions with previous trauma history such as insect bites or needle injuries. Skin and soft tissue infections develop in approximately 75~90% cases of disseminated Fusarium infection1. According to previous re- ports, the upper and lower extremities are the most common sites. Common morphologic types of skin lesions include red or gray papular and macular type lesions with central eschar and necrosis and subcutaneous nodular type lesions1. Previous studies have reported various skin lesions such as necrotic tissue, cellulitis with necrosis, ulceration, and plaque type with vesicles and pustules in immunocompetent patients. Most of these patients had a history of skin breakdown such as burns, trauma, and preexisting onychomycosis₅.

Most Fusarium species are resistant to antifungal agents2,3. In particular, F. solani SC shows high resistance to various antifungal agents6 and has high minimal inhibitory concen- tration to many azoles including posaconazole, itraconazole, and difenoconazole₄. The ideal treatment regimen for Fusarium infections is controversial. Combination therapy of liposomal amphotericin B and voriconazole is most commonly used6. However, unlike immunocompromised patients, cases successfully treated by oral itraconazole or local heat therapy have been reported_7,8. In this case, the patient was effectively treated with oral itraconazole, and he had no recurrence during the 12-month follow-up period.