Incidence of congenital triangular alopecia*

To the Editor, We read with interest the excellent article titled “Use of dermoscopy in the diagnosis of temporal triangular alopecia” by Campos et al.1 However, we take issue with their statement that the incidence of congenital triangular alopecia has been estimated at 0.11%.2 Taken at face value, readers may assume that 0.11% of the general population have congenital triangular alopecia. The 0.11% number was derived from the study by Garcia-Hernandez et al. They reviewed 6,200 randomly selected patients seen for the first time at a dermatology clinic at the Virgen Macarena University Hospital in Spain, and found that 7 (0.11%) patients had congenital triangular alopecia.2 We would like to point out that the population studied was highly selective and did not represent the true incidence among the general population. Congenital triangular alopecia was first described in 1905 by Raymond Sabouraud in his book “Manuel elementaire de dermatologie topographique regionale” as “alopecia triangulaire congenitale de la temp.”3 Li et al. identified only 126 cases of congenital triangular alopecia in the published literature, cited on Pubmed between 1905 and 2015.4 Patients may not seek medical attention for this benign and asymptomatic lesion, while many may be undiagnosed or misdiagnosed. Both factors could explain the scarcity of reported cases. We are under the impression that congenital triangular alopecia is more common than currently appreciated. With increased awareness of this condition, many more cases will conceivably be reported. Recently, a 3-year-old Chinese girl presented to us with an 18-month history of a localized triangular area of hair loss in the right frontotemporal area. We searched in the literature but could not find the incidence of congenital triangular alopecia in the general population. It is hoped that properly designed studies will better elucidate the incidence of congenital triangular alopecia in the general population.q