Sir,

Acanthosis nigricans (AN) is a keratinizing disorder characterized clinically by symmetric hyperpigmented plaques with a papillomatous or verrucous surface. It is most frequently associated with systemic conditions such as obesity, metabolic syndrome, diabetes mellitus, and internal malignancies [1]. In contrast, nevoid AN is a rare and benign variant that typically lacks any association with systemic disease [2]. Clinically, nevoid AN presents as asymmetrical hyperpigmented plaques with a segmental or localized distribution, often appearing during childhood or adolescence. Here, we report two cases of nevoid AN developing in close association with surgical scar sites.

The first case involved a 15-year-old boy who had undergone surgery for acute appendicitis via an umbilical incision six years prior to presentation. Three years before referral, a dark brown nodule appeared at the umbilicus and gradually increased in size. He was referred to our department for further evaluation and management. Physical examination revealed a dark brown, papillomatous nodule protruding from the umbilical fossa, surrounded by scattered small brown nodules in the periumbilical area (Fig. 1a). Histopathological examination demonstrated marked hyperkeratosis with papillomatous epidermal hyperplasia and upward elongation of the dermal papillae, including focal spire-like projections. Basket-weave hyperkeratosis was evident within epidermal invaginations (Fig. 1b). Periodic acid–Schiff and methylene blue staining revealed yeast-like fungal elements within the stratum corneum (Figs 1c and 1d). Based on these findings, the involvement of Malassezia infection was suspected, and topical luliconazole therapy was initiated. After two months of treatment, the brown periumbilical nodule had completely resolved (Fig. 1e).

Figure 1: (a) Clinical presentation of the first case at first visit. (b) Histological examination of the first case (hematoxylin and eosin, ×40). (c, d) PAS and methylene blue staining (×400). (e) Two months after topical luliconazole. (f) Clinical presentation of the second case at first visit. (g) Histological examination of the second case (hematoxylin and eosin, ×40). (h) After the treatment with topical corticosteroids and vitamin D3 analogs.

The second case involved a 51-year-old man who had undergone surgery for pneumothorax 20 years earlier via a right thoracic incision. He presented with pruritus, hyperpigmentation, and exudative discharge localized to the right chest. Clinical examination revealed multiple brown nodules on the right anterior chest, accompanied by several reddish-brown nodules on the dorsal aspect (Fig. 1f). Histopathological examination showed papillomatous epidermal hyperplasia with basket-weave hyperkeratosis in the epidermal invaginations (Fig. 1g). No yeast-like fungal elements were detected by special staining. The lesions showed marked improvement following treatment with topical corticosteroids and vitamin D₃ analogs (Fig. 1h).

The precise pathogenesis of nevoid AN has not yet been fully elucidated. Previous studies have suggested that mosaic mutations in FGFR3 and FGFR2 may play a role in its development [3]. In addition, fungal infection has been proposed as a possible contributing factor in certain cases [4]. In the present report, yeast-like fungal elements were detected in the first case but not in the second, suggesting heterogeneity in the underlying mechanisms. Treatment options for AN include oral etretinate, topical vitamin D₃ analogs, and urea-containing topical preparations [1]. The favorable response observed in the second case indicates that topical anti-inflammatory therapy may also be effective in selected patients. As demonstrated in these two cases, the development of nevoid AN at surgical scar sites may be associated with disturbances in local tissue homeostasis caused by postoperative inflammation and/or secondary fungal infection. However, further accumulation of similar case reports is required to clarify the exact mechanisms underlying this phenomenon.

REFERENCES

1.  Das A, Datta D, Kassir M, Wollina U, Galadari H, Lotti T, et al. Acanthosis nigricans:A review. J Cosmet Dermatol. 2020;19:1857-65.

2.  Choudhary R, Thakur V, Hanumanthu V, Chatterjee D, Kumaran MS, Vinay K. Nevoid acanthosis nigricans:a case series of nine patients. Int J Dermatol. 2022;61:e425-7.

3.  Larsabal M, Cogrel O, Caumont C, Jegou MH, Taieb A, Morice-Picard F. Mosaic mutations in FGFR3 and FGFR2 are associated with naevoid acanthosis nigricans or RAVEN (round and velvety epidermal naevus). Br J Dermatol. 2019;180:201-2.

4.  Matsumoto A, Nakai K, Tsuruta D, Sugawara K. A Case of Nevoid Acanthosis Nigricans Successfully Treated with Topical Ketoconazole Plus Urea. Acta Dermatovenerol Croat. 2021;29:167-8.