Sir,

Benign skin tumors are the most common types of skin tumors and are characterized by a wide clinical and histological variety. They result from an abnormal proliferation of a skin component without local or distant invasion as is the case of cutaneous adnexal tumors originating from the hair follicle, sebaceous, eccrine, or apocrine glands [1].

Herein, we report here a case of inverted follicular keratosis in a sixty-year-old patient, which was a rare cutaneous adnexal tumor.

A north-African, previously healthy sixty-year-old patient presented to our department with a papule developing over the previous three years. Clinical examination revealed a pearly pink papule of 4 mm located above the upper lip. The rest of the physical examination was unremarkable (Fig. 1).

Figure 1: Pearly pink papule of 4 mm located above the upper lip.

Dermoscopy showed a pinkish-white background, a scaly surface, whitish structureless areas, and polymorphous radial vessels: linear, arborizing, and hairpin vessels surrounded by a white halo (Fig. 2).

Figure 2: Dermoscopic image showing pinkish-white background, a scaly surface (black asterisks), whitish structureless areas, and polymorphous radial vessels: linear (red arrow), arborizing (black arrow) and hairpin vessels (black circle) surrounded by a white halo.

Histopathology examination demonstrated an endophytic tumor with large lobules extending into the dermis composed of basaloid cells at the periphery and squamous keratinizing cells toward the center, with the presence of squamous eddies. Overlying the tumor there was hyperkeratosis and parakeratosis with occasional keratinous plugs. These histological features are characteristic of an inverted follicular keratosis (Figs. 3a and 3b).

Figure 3: (a) Histologic images of an endophytic tumor with large lobules extending into the dermis. Overlying the tumor there was hyperkeratosis and parakeratosis with occasional keratinous plugs (H&E; 10×). (b) Histologic images of inverted follicular keratosis (H&E; 20×).

Inverted follicular keratosis is a benign follicular tumor that was first described in 1954 by Helwig as a lesion characterized histologically by the presence of invaginating, cup-shaped, and finger-like tumor masses [2].

It originates from the infundibular portion of the hair follicle and most often occurs in male Caucasian elderly patients, usually localized on the cephalic extremity: head and neck.

As for the clinical presentation, it is a lesion that may cause concern due to its unique character, whitish-pink color, and firm consistency. However, it usually remains an asymptomatic lesion, generally measuring less than 1 cm in diameter [3].

Dermoscopy may reveal a pinkish-white background with central crust, ulceration, or whitish-orange structureless areas and polymorphous radial vessels: hairpin, comma, glomerular, and linear and arborizing surrounded by a white halo mimicking mainly a Bowen disease, and actinic keratosis or a basal cell carcinoma [4].

The diagnosis is confirmed by histopathology that reveals an endophytic tumor constituted by basaloid cells at the periphery and larger keratinizing cells toward the center, with hyperkeratosis and parakeratosis [4].

The treatment primarily relies on surgery, which enables complete healing with no recurrence [5]. However, other treatments have been reported in the literature, such as 5% imiquimod, which was used in a 73-year-old Caucasian patient at a frequency of three times per week, resulting in an almost complete regression of the lesion two months later [6].

The diagnosis of inverted follicular keratosis should always be kept in mind in front of a single papule on the face, particularly in elderly male patients. Dermoscopy may guide us, yet the confirmation of the diagnosis remains histological to eliminate other malignant tumors.

Surgical excision represents the gold standard treatment for this adnexal benign tumor.

REFERENCES

1. Lai M, Muscianese M, Piana S, Chester J, Borsari S, Paolino G, et al. Dermoscopy of cutaneous adnexal tumours:A systematic review of the literature. J Eur Acad Dermatol Venereol. 2022;36:1524-40.

2. Mehregan AH. Inverted follicular keratosis. Arch Dermatol. 1964;89:229-35.

3. Shah R, Maddukuri S, Patel S, Behbahani S, Skula S, Lambert WC. Inverted follicular keratosis:Stand-alone entity or variant. Skinmed. 2019;17:93-4.

4. Savoia F, Patrizi A, Tabanelli M, Vaccari S, Sacchelli L, DI Altobrando A. Inverted follicular keratosis:Dermoscopic features of 23 cases. Ital J Dermatol Venerol. 2021;156(Suppl. 1):102-3.

5. Thom GA, Quirk CJ, Heenan PJ. Inverted follicular keratosis simulating malignant melanoma. Australas J Dermatol. 2004;45:55-7.

6. Karadag AS, Ozlu E, Uzuncakmak TK, Akdeniz N, Cobanoglu B, Oman B. Inverted follicular keratosis successfully treated with imiquimod. Indian Dermatol Online J. 2016;7:177-9.