Dermatoscopic profiling of inverted follicular keratosis in different skin phenotypes

Inverted follicular keratosis (IFK) is a rare benign tumour of the follicular infundibulum. Owing to its similarity to other benign and malignant cutaneous lesions, it poses a diagnostic challenge. There is limited information on the dermatoscopic characteristics of IFK and the majority of cases have been reported in patients with lighter skin types.

To describe the prevalent dermatoscopic features of IFK, especially in patients with skin of colour.

We retrospectively analysed 35 histopathologically verified cases of IFK from a single university hospital in Turkey.

With respect to the Fitzpatrick skin phototype, 2 (6%), 12 (34%), 16 (46%) and 5 (14%) patients had Fitzpatrick skin phototypes II, III, IV and V, respectively. Clinically, the majority of IFKs were hypopigmented or nonpigmented (83%). Pink-white structureless areas (54%), ulceration (54%), a central keratin mass (43%) and blood spots on keratin mass (43%) were the most frequent dermatoscopic findings. Pigmented structures were observed as blue-grey structureless areas in 12 lesions and as blue-grey clods in 5, primarily in Fitzpatrick phototype IV and V skin. The incidence of a pink, structureless area and blood spots on ulceration was found to be statistically significantly higher in individuals with fairer skin types, while a greater prevalence of blue-grey coloration was observed in those with skin of colour (P < 0.05).

Although our study found some distinguishing dermatoscopic findings in IFK, diagnosis is generally confirmed by histopathology, as the clinical appearance and dermatoscopic findings may not be sufficient to differentiate it from other tumours, especially squamous cell carcinoma or keratoacanthoma. The dermatoscopic characteristics of dark skin are comparable to those of pale skin; however, hyperpigmentation can be more noticeable in skin of colour.