The Diagnosis: Temporal Triangular Alopecia
Temporal triangular alopecia (TTA), also known as congenital triangular alopecia, was first described in the early 1900s.1 It presents clinically as a triangular-shaped area of nonscarring alopecia either unilaterally or bilaterally. Limited clinical data suggest that most unilateral cases are on the left frontotemporal region of the scalp. In bilateral cases, there may be asymmetry in size of the area involved.2 Dermatoscopically, TTA is characterized by decreased terminal hair follicle density as well as the presence of vellus hairs with an absence of inflammation.3 The majority of TTA is noted between birth and 6 years of life with the areas staying stable thereafter. Large areas of TTA may suggest cerebello-trigeminal-dermal dysplasia (Gomez-Lopez-Hernandez syndrome), a rare neurocutaneous syndrome characterized by rhombencephalosynapsis, trigeminal anesthesia, and parietooccipital alopecia (Online Mendelian Inheritance in Man 601853).4 Although TTA is largely idiopathic, it has been suggested that the trait may be paradominant, whereby a postzygotic loss of the wild-type allele in a heterozygotic state causes triangular alopecia and reflects hamartomatous mosaicism.5 It also is an important mimicker of alopecia areata. Correct identification prevents unnecessary treatment to the areas of the scalp. Hair restoration surgery has been reported as a tool to treat this disorder.6