Congenital triangular alopecia

Figure 1a. CTA of left frontotemporal in a 5-year-old girl which was noticed from aged 2.

Figure 1b. Dermoscopic image of CTA (DermLite DL4, polarized): red-circle (vellus hairs), yellow-circle (terminal hair) without exclamation mark & brittle hairs, and black and yellow dots.

A congenital triangular alopecia (CTA), also termed as temporal triangular alopecia (TTA) is a localized non-inflammatory and non-scarring alopecia which is clinically characterized by a smooth bald patch on the left or right side of frontotemporal scalp with triangular, spear or oval shape (Figure 1a). Bilateral frontotemporal or other site involvement is rare. It was first described by Sabouraud in 1905 as “alopecia triangulaire congenitale de la temp”.^[1] Dermoscopic/trichoscopic features of CTA (Figure 1b) include: ^[2,3,4]

• Normal follicular openings with vellus hairs centrally and terminal hairs at the periphery the bald patch.
• Absence of ‘exclamation mark’, broken or dystrophic hairs.
• Absence of black and yellow dots.

Precise etiopathogenesis of CTA remains unclear. It is suggested as, acquired as well as congenital origin.^[5] Most cases usually start to present between aged 2 - 9 years, and remains stable throughout the life.^[3,4] CTA has no predilection for sex and race. Earlier publications reported mainly affecting white people,^[2,3] however several reports exist affecting non-European origin as well.^[4,5,6,7] The differential diagnoses for CTA include alopecia areata, traction alopecia, trichotillomania, and congenital aplasia cutis.^[3,4,5] Diagnostic criteria for CTA/TTA should include by incorporating Inui et al’ proposal^[2] :

1. Clinical factors: age, pattern and location of alopecia as described above
2. Dermoscopic/trichoscopic features: as described above
3. Period: No significant hair regrowth (with or without treatment) 6 months after confirmation of the existence of vellus hairs clinically and dermoscopically.

No effective treatment has been reported for CTA, and surgical excision (if the area is small), or hair transplant may be considered.^[5,7]

Conflict of interests: nil

References:

1. Sabouraud R. A Manual of Regional Topographical Dermatology. Paris: Masson; 1905. p 197.
2. Inui S, Nakajima T, Itami S. Temporal triangular alopecia: trichoscopic diagnosis. J Dermatol. 2012 Jun;39(6):572-4.
3. Campos JG, Oliveira CM, Romero SA, Klein AP, Akel PB, Pinto GM. Use of dermoscopy in the diagnosis of temporal triangular alopecia. An Bras Dermatol. 2015 Jan-Feb;90(1):123-5.
4. Viswanath V, Kalambe V, Sanap D. Congenital triangular alopecia: Clinical and dermoscopic differentials. Indian J Paediatr Dermatol 2019;20:75-7.
5. Patel DR, Tandel JJ, Nair PA. Congenital Triangular Alopecia - A Case Report. Int J Trichology. 2020 Mar-Apr;12(2):89-92.
6. Zhao YL, Zhang RZ. Congenital Triangular Alopecia: A Brief Report. Int J Trichology. 2018 Nov-Dec;10(6):290-291.
7. Aung T. A solitary triangular alopecia. Med J Aust. 2023 Apr 28. doi: 10.5694/mja2.51940.