Verrucous Cutaneous Candidiasis on the Dorsum of the Finger

We report a case of verrucous plaque initially diagnosed as verruca vulgaris, but later identified as verrucous cutaneous candidiasis based on histopathological findings, fungal culture, and polymerase chain reaction (PCR) results. The lesion resolved following topical treatment with an antifungal drug. A 68-year-old man, with no occupational or recreational exposure to soil or plants, noticed a plaque on the dorsal surface of his right index finger three years earlier. As the plaque had gradually enlarged over the month prior to presentation, he sought medical evaluation at our hospital. At the first visit, a verrucous, slightly pinkish plaque measuring 20 × 15 mm was observed, and was neither painful nor itchy (Figure 1a). Dermoscopy revealed black dots and bleeding on an erythematous background, along with a whitish papillomatous structure (Figure 1b), suggestive of verruca vulgaris [1], but the absence of multiple small pustules or small, round structures surrounded by a reddish halo as shown in a case of cutaneous candidiasis [2]. Although the clinical and dermoscopic findings initially suggested verruca vulgaris, a skin biopsy was performed to exclude verrucous squamous cell carcinoma. Histopathological examination revealed hyperkeratosis, parakeratosis, epidermal hypertrophy, elongation of the rete ridges, and infiltration of mononuclear cells in the upper dermis by hematoxylin–eosin staining (Figure 1c). Periodic acid-Schiff and Alcian blue staining demonstrated numerous pseudohyphae in the stratum corneum (Figure 1d,e), but human papilloma virus (HPV) immunostain (K1H8) was negative. Microscopic examination using a 15% potassium hydroxide (KOH) solution revealed fungal elements (Figure 1f). Fungal culture on Sabouraud agar medium produced white creamy colonies characteristic of Candida species (Figure 1g). Fungal and HPV PCR analyses were subsequently performed. Briefly, formalin-fixed paraffin-embedded sections were subjected to PCR using fungal primer pairs (ITS1/ITS2, ITS3/ITS4, and ITS1/ITS4), with positive amplification observed [3]. Sequencing of the PCR products identified the organism as Candida albicans (Figure 1h). PCR for HPV using four primer pairs (CP IIs/CP-I, GP5+/GP6+, L1C1/L1C2, SKF1/SKF2, and SKR/SKR2) was negative. Based on these findings, a diagnosis of verrucous cutaneous candidiasis was made. Topical clotrimazole was applied, resulting in clinical improvement and the disappearance of fungal elements on microscopic examination using a KOH solution after two months. Cutaneous candidiasis is generally classified into superficial and deep infections, with most cases being superficial. The infection typically manifests as erythema, vesicles, pustules, and scaling in intertriginous areas, interdigital spaces, perionychia, or vulva. Atypical cutaneous candidiasis, including papillary hyperkeratosis and hyperkeratotic candidiasis, has been rarely reported [4]. However, most cases may be misdiagnosed as verruca vulgaris. The present case was considered a wart-like lesion caused by a C. albicans infection. Both HPV immunostaining and PCR were negative in the present case. It has been proposed that Th1 cells and macrophages induced by Candida antigens may eliminate HPV [5]; therefore, the possibility that preexisting verruca vulgaris was eradicated by C. albicans infection cannot be excluded. In conclusion, cutaneous candidiasis should be considered in the differential diagnosis of verrucous plaques. The authors have nothing to report. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.