Paediatric-Onset Folliculitis Decalvans and Lichen Planopilaris Phenotypic Spectrum: Is It a Different Disease?

Folliculitis decalvans (FD) and lichen planopilaris (LPP) are classified as neutrophilic and lymphocytic cicatricial alopecias respectively. FD and LPP have distinctive clinical, trichoscopic and histopathological features. Cases with concomitant or sequential features of both forms of primary cicatricial alopecia (PCA) have been described since 2020, and the term folliculitis decalvans and lichen planopilaris phenotypic spectrum (FDLPPPS) has been proposed. This study aimed to describe the clinicopathological features and response to treatment of patients who developed FDLPPPS in childhood. A retrospective review of patients with FDLPPPS with an age of onset of ≤ 18 years seen in three dermatology clinics in Australia and one in Lebanon from August 2020 to February 2024 was conducted. Fourteen patients (10 females and four males) with a mean (SD) age of onset of 12.4 (4.4) years were identified. Five patients had genetic or congenital abnormalities, and two patients were sisters. Scalp symptoms included itch (n = 8), pain or tenderness (n = 5) and flaking (n = 1), with clinical signs of crusting (n = 12), erythema (n = 10) and pustules (n = 3). Seven patients presented with a solitary plaque and seven with multiple plaques, most commonly affecting the vertex scalp (n = 13). Histopathological examination showed a perifollicular lymphocytic infiltrate and concentric lamellar fibrosis in 13 and 14 cases respectively. Keratosis pilaris (KP) or one of its variants was observed in eight cases. Treatment led to disease stabilisation in seven cases, but hair loss progressed in six cases. FDLPPPS is an aggressive form of primary cicatricial alopecia that can rarely begin in childhood. Given the clinical features and association with KP or its variants in a significant proportion of our patients, we hypothesise that FDLPPPS may be a sequela of a disorder of keratinisation.