Circle hairs: clinical, trichoscopic and histopathologic findings.

Circle hairs (CH) represent a body hair growth disorder characterized by asymptomatic presence of hairs with typical circular or spiraliform arrangement, not associated with follicular or inflammatory abnormalities. Although this condition is rarely reported, it is probably underestimated, as a medical consultation for CH only is rare in practice. Trichoscopic and histopathological findings of CH have never been reported and this article will present and discuss six cases along with literature review.

INTRODUCTION

Circle hairs (CH) represent a body hair growth disorder characterized by asymptomatic presence of hairs with typical circular or spiraliform arrangement, not associated with follicular or inflammatory abnormalities;[1234] they are almost exclusively seen on the trunk and upper legs of male overweight patients, where they are interspersed with normal hairs. Clinical, trichoscopic and histopathologic findings of six cases of CH are presented and discussed along with literature review.

CASES REPORT

Six Caucasian adult males came to our observation for the evaluation of different cutaneous disorders, as described in [Table 1]. During physical examination, in all patients was noticed the presence of several CH, among normal hairs, especially on the trunk and thighs [Figures 1a–2a; no signs of inflammation or follicular abnormalities were present. No specific association with other dermatoses and/or systemic diseases has been evidenced in any patient. Trichoscopy at ×150 magnification [Figures 1b and c, 2b and c, 3a–c] showed in all cases no shaft abnormality and evidenced that some of these CH were located under a thin skin layer corresponding to outer stratum corneum, whereas others were protruding out of skin; most of CH showed an almost perfect round configuration. After pulling, CH showed a characteristic “question mark” appearance [Figure 3d]. In two patients (Patients 1 and 4) a biopsy was performed and histopathologic evaluation showed that hair follicle density was normal, with intermediate, miniaturized, anagen and catagen hair follicles and no inflammatory perifollicular infiltrate. Moreover, “river-bed”, dilated, follicle infundibula, with entrapped hair shafts, were observed [Figures 1d–2d].

Table 1

Patients with circle hairs: Our experience

Figure 1

Patient 1: Several dark circle hairs (CH), among normal hairs, on the abdomen (a); trichoscopy at ×150 showing CH protruding from the skin (b) or located under a thin skin layer (c); histopathology showing a “river-bed”, dilated, follicle infundibulum, with an entrapped hair shaft (d)

Figure 2

Patient 4: Clinical (a), trichoscopic (b, c) and histopathologic (d) aspect of circle hairs

Figure 3

Patients 2 (a), 3 (b), 5 (c): Trichoscopic aspect of circle hairs (CH). Patient 6 (d) Characteristic “question mark” appearance of CH after pulling

DISCUSSION

After the initial description of 16 cases by Adatto, another seven cases of CH have been clinically, but not histologically, described in the English literature [Table 2]. Although this condition is rarely reported, it is certainly underestimated, as medical consultation for CH is rare in practice. As in our cases, all reported patients with CH were adult males and the most frequent localization was the back.

Table 2

Patients with circle hairs: Cases reported in the literature

The pathogenesis of CH remains obscure. According to some authors, CH have a small hair diameter that make it difficult to penetrate stratum corneum and, for this reason, the hair grows in a circular tract and in a subcorneal location.[3] Other authors do not agree with this hypothesis, claiming that the follicular ostia are continuously open and hence that the hair does not need to perforate the stratum corneum: Based on this, they maintain that CH are probably a genetically pre-determined disorder.[4] The possibility that CH correspond to vestigia (or remnants) of the mammal undercoat has also been suggested.[4]

Trichoscopy is a non-invasive technique that has been utilized for the evaluation of different hair disorders.[56789] In our cases, it showed that CH did not present any shaft abnormality. Moreover, it displayed that some CH were located under a thin skin layer, whereas others were protruding from the skin. A possible explanation for this is that the “rolling” initially takes place below the stratum corneum; then, with epidermis turnover, the hair protrudes from the skin.

The histopathology of CH has not previously been adequately described. In our cases, it showed the presence of a “river bed” dilated follicle infundibulum with entrapped hair shaft. Both hair follicle density and hair diameter resulted normal. We found no evidence of inflammatory infiltrate and no obstruction at the level of the follicular ostia that might have hampered hair growth, confirming that the follicular ostia are open. Whether the dilated infundibulum is the primary cause of CH, or secondary to the subcorneal hair growth, remains to be established and could represent an area of future research.

Differential diagnosis of CH mainly includes “rolled hairs”, which are not perfectly circular, but may appear as irregularly coiled within a hyperkeratotic papule and associated with signs of inflammation and, often, with abnormalities of keratinization, such as atopic dermatitis, ichthyosis and palmoplantar keratoderma.[4]