Clinical and histopathological features in inverted follicular keratosis

Background: Inverted follicular keratosis has distinctive histopathological features and is infrequently encountered by dermatologists. To date, the pathogenesis of inverted follicular keratosis has not been elucidated. Many authors have suggested several theories for the nature of inverted follicular keratosis including verruca vulgaris with squamous eddies, irritated seborrheic keratosis and distinctive follicular tumors. There are no comprehensive studies about the clinical and histopathological features of inverted follicular keratosis in Korea. Objective: The purpose of this study was to analyze the clinical features and histopathological findings of inverted follicular keratosis with literature review. Methods: We studied 14 patients with inverted follicular keratosis for clinical features including the duration of the disease, the location and size of the lesions, the clinical impressions at the first visit and we made a record of the patients' age and sex, histopathological findings. Results: 1. Eight of the 14 patients were male and the ages ranged from 40 to 83 years (mean 59.3 years). The lesions were situated on the face (5/14), scalp (3/14), abdomen (2/14), hand (2/14), buttocks (1/14), shin (1/14). The average size of the lesions was 1.38cm. 2. Seborrheic keratosis was the most common clinical diagnosis (6/14), followed by verruca vulgaris (4/14), cutaneous horn (1/14), melanoma (1/14), soft fibroma (1/14) and pigmented nevus (1/14). 3. Solid and nodular types were the most common histopathological type (7/14), followed by keratoacanthoma-like type (5/14), filiform or wart like type (2/14). Conclusion: Inverted follicular keratosis have unusual clinical and histopathological features. We recommend that verrucous plaque lesions should be diagnosed correctly by histopathologic examination and it may be helpful to avoid inappropriate therapeutic approach.