Congenital Triangular Alopecia.

Congenital triangular alopecia (CTA) also known as temporal triangular alopecia is a benign noncicatricial pattern of hair loss. It typically affects the frontotemporal region and rarely involves the temporoparietal or occipital scalp. It is a nonprogressive disorder that presents as a triangular, oval or lancet-shaped patch of alopecia. CTA can manifest at birth or develop later in life. The exact etiology of this condition remains unknown. Rarely, it may be associated with other disorders such as Down's syndrome and phakomatosis pigmentovascularis. The diagnosis is based on its distinct clinical appearance. Histologically, hair follicles are miniaturized and replaced by sparse vellus hair follicles. Tricoscopy using a polarized light handheld dermatoscope can be a useful diagnostic tool. CTA is often asymptomatic and remains unchanged throughout the life. No treatment is required. Surgical intervention with follicular unit hair transplantation can provide a satisfactory cosmetic result. In this paper, we have identified 126 cases of CTA in the published literature cited on PubMed between 1905 and 2015. From the available evidence, 79% of patients with CTA presented with unilateral hair loss, 18.5% with bilateral involvement and rarely, with occipital alopecia (2.5%). There was no gender predilection. These figures are entirely consistent with previously published data. Physicians should remember to consider CTA as a potential diagnosis in any patient presenting with a nonscarring alopecia in order to avoid unnecessary investigations and treatments.

INTRODUCTION

Congenital triangular alopecia (CTA) also known as temporal triangular alopecia, or Brauer nevus, is a benign noncicatricial localized pattern of hair loss. This condition was first described in 1905 by Raymond Sabouraud in his book “Manuel élémentaire de dermatologie topographique réégionale” as “alopecia triangulare congenitale de la temp.”[1] As of January 2015, 126 cases have been reported worldwide, as shown in Table 1.[234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950] It typically affects the frontotemporal region [Figures 1 and 2], although there have been reported cases of CTA affecting the temporoparietal[154246] and occipital scalp.[3637] It is a nonprogressive disorder, which presents as a triangular, oval or lancet-shaped patch of alopecia.[14] CTA may manifest at birth or develop in adulthood.[18] The incidence in the general population is estimated to be 0.11%.[15]

Table 1

Summary of 126 cases of congenital triangular alopecia

Figure 1

Congenital triangular alopecia affecting the frontotemporal regions bilaterally in an 8-year-old girl (left frontotemporal hair loss shown in this photograph) (This photograph is original courtesy of Dr. Paul Yesudian)

Figure 2

Congenital triangular alopecia affecting the frontotemporal regions bilaterally in an 8-year-old girl (right frontotemporal hair loss shown in this photograph) (This photograph is original courtesy of Dr. Paul Yesudian)

BACKGROUND

Congenital triangular alopecia is usually unilateral but may be bilateral in up to 20% of cases.[14] The condition remains unchanged throughout the life.[8] There is no gender predilection.[28] Most of the reported cases were in Caucasian patients, although CTA has also been documented among Asians[91119253537384142444547] and African-Americans.[24] In a published series of 53 patients by Yamazaki et al.[35] in 2010, more than ½ (58.8%) of the cases appeared in patients between the ages of two and nine, while over a third (36.5%) manifest at birth and 3.8% presented in adulthood. From our literature review, 79% of patients with CTA presented with unilateral hair loss while 18.5% of patients had bilateral involvement. About 2.5% consulted with occipital alopecia and 51.6% of the patients were male, versus 48.4% of females. These figures are consistent with previously published data.

Clinical features

Most reported lesions of CTA have been described as lacking any hair, although a few normal terminal or vellus hairs may be evident within the affected patch [Figure 3]. In addition, CTA may not present as a completely bald patch but instead show a centrally localized hair tuft[33] or as small islands of dark hairs.[12]

Figure 3

Triangular patch of hair loss over the left frontotemporal region; normal terminal or vellus hairs may be noted within the affected patch (This photograph is original courtesy of Dr. Paul Yesudian)

Kubba and Rook[8] noted that in the vast majority of cases the area of alopecia was not noted by a child's parents until after 3 years of age. This latency period is attributed to the relatively sparse pelage during the 1st year of life.[14] Parents may only become aware of the affected patch when it contrasts significantly with the surrounding hair,[8] as the vellus hairs are replaced by terminal hair.

Etiology

Once considered congenital, CTA appears to be acquired in the majority of individuals.[42] It usually appears sporadically although there have been a small number of familial cases.[52022] It has been postulated that CTA may reflect mosaicism[4246] and may be inherited as a paradominant trait where a postzygotic loss of the wild type allele in a heterozygote state leads to disease.[51] Others have suggested that CTA may be an ectodermal defect and should be included in the group of epidermal nevi.[22] There is currently no consensus, and the exact etiology of this condition is unclear. There appears to be no obvious phylogenetic or embryological explanation for CTA.[8] Nonetheless, the development of CTA in the 1st year of life in an area of the scalp that had previously appeared normal is strongly indicative of a localized process of miniaturization of the hair follicles, which produces regression to vellus hair.[2945] The stimulus responsible for this irreversible regression remains unknown.

Histology

In CTA, normal terminal hair follicles are typically replaced by sparse vellus hair follicles.[7] The total number of hair follicle units are usually in the normal range,[1445] except for an isolated case report of a decreased number of hair follicles.[31] The epidermis and dermis are unremarkable[131418] with no evidence of an inflammatory infiltrate.[1442] However, hair follicles are miniaturized[354546] with an increased proportion of vellus or indeterminate hairs.[14184550] This may be due to abnormalities in follicle morphogenesis and supports the idea that CTA is a form of a hamartomatous mosaic disease possibly involving an abnormal, local, epithelial-mesenchymal interaction.[35] Collagen bundles and vessels in the dermis shows no abnormalities; sweat glands and sebaceous glands are normal in size and number.[35] Bacterial and fungal stains are negative.[18]

Diagnosis

The diagnosis of CTA is mainly clinical and based on its distinct clinical appearance and location. It is not dependent on histology. Sometimes, CTA may be misdiagnosed as other types of localized alopecia that present with a small, round or oval hairless patch in atypical locations on the scalp. Common differential diagnoses, which should be considered, are listed in Table 2.

Table 2

Differential diagnoses of congenital triangular alopecia

A classification system for the diagnosis of CTA proposed by Inui et al.[38] emphasized the importance of four main clinical features. (1) A triangular or spear-shaped patch of hair loss located over the frontotemporal region of the scalp; (2) normal hair follicles with vellus-type hairs surrounded by a normal terminal hair area; (3) absence of fractured or exclamation mark hairs and no black or yellow dots with a preserved follicular orifice; and (4) lack of significant hair growth 6 months after confirming the presence of vellus hairs on dermoscopy.

Associations

Congenital triangular alopecia is associated with other disorders in up to 15% of cases[50] and may occur as a key feature in a multiple malformation syndrome.[28] Common associated features are listed in Table 3and syndromes in Table 4.

Table 3

Reported disorders presenting in association with congenital triangular alopecia

Table 4

Reported syndromic associations

Investigations

Trichoscopic examination using a handheld polarized light dermatoscope has emerged as a helpful diagnostic tool as it can help to elucidate clinical signs that cannot be recognized by the naked eye.[48] Follicular features of CTA include short vellus hairs with varying hair length diversity, as well as white hairs in the absence of diagnostic features for other types of localized alopecia.[48] The presence of epidermal scaling, as well as interfollicular features such as arborizing red lines and a honeycomb pigment pattern, may also be useful clues.[48] Vellus hairs are a highly sensitive but not specific marker for CTA.[48] A study by Shim et al.[52] demonstrated clustered short vellus hairs without other specific findings. Videodermoscopy has also been used.[53] The hair pull test was negative in all reported cases.[284648]

Treatments

Congenital triangular alopecia is often asymptomatic and remains unchanged throughout the life; it is likely that many patients do not consult a physician for this particular condition.[13] It is viewed as a permanent condition with no specific treatment necessary except for cosmetic reasons. The exact nature of CTA should be explained to parents so that they can avoid fruitless investigations or harmful treatments.[28] Medical treatment of CTA with topical or intralesional corticosteroids have not proved effective.[29] Bang et al.45reported a successful case of transient improvement with the use of 3% topical minoxidil in a 1-year-old child. Terminal hair growth was observed. Unfortunately, hair regrowth was not sustained following the cessation of treatment. Hair restoration surgery using follicular unit transplantation or surgical excision may provide patients with a satisfactory cosmetic result.[2932404145] Long-term sustained benefits have been reported after 6 years of follow-up.[40]

CONCLUSION

Congenital triangular alopecia is likely underreported and in reality, not an uncommon disorder. It may be underdiagnosed due to diagnostic confusion with other types of nonscarring alopecia[50] and under reported due to its asymptomatic and nonprogressive nature.[42] Future advances in molecular and genetic studies will help to reveal the exact etiology this condition.[35] Unnecessary treatments such as topical corticosteroids may be avoided; to achieve this, one must remember to consider CTA as a possible diagnosis in any patient presenting with a nonscarring alopecia.