Extensive pili multigemini over the back.

Pili multigemini is a rare disorder where more than one hair exists in a single hair follicle. Papillar tips that divide into several tips will produce several hair shafts, so that characteristically do not fuse again. This disorder is relatively frequent on the beard of adult men and on the scalp of children. However, extensive areas of pili multigemini in other locations have rarely been described.

INTRODUCTION

Pili multigemini is an unusual hair follicle dysplasia. This disorder is relatively frequent on the beard of adult men and on the scalp of children.[1] However, extensive pili multigemini involving large areas has rarely been described.[2]

CASE REPORT

A 33-year-old man was referred for evaluation of an itchy sensation on his back that had been present for more than 10 years. Physical examination revealed a large patch with short and irregular hairs that involved his entire back [Figure 1a]. The patient remarked that those hairs had never grown longer. Hair appearance in other areas of the body was completely normal. Dermoscopic evaluation showed that hair follicles contained several short hair shafts with different lengths [Figure 1b]. Histological examination revealed that the follicular structures consisted of different hair shafts, which were enclosed in a common outer root sheath [Figure 2]. These findings suggest the diagnosis of pili multigemini. Each hair had its own inner root sheath.

Figure 1

(a) Physical examination revealed an extensive and well demarcated patch with short and irregular hairs that involved the entire back (b) Dermocopic image shows that hair follicles contained several short hair shafts with different lengths

Figure 2

Histologic image. Follicular structures include different hair shafts (yellow arrows), which were enclosed in a common outer root sheath

DISCUSSION

Pili multigemini is a hair disorder characterized by clusters of shafts that emerge from a single follicle.[345] A common bulb encloses a dermal papilla that splits into different-sized hair shafts with separate cuticles.[6] The strands of hair emerge together through a single hair canal. Normal hair grows from a single hair follicle and exits from one hair canal to the surface of the skin. The cause of pili multigemini is unknown, although there may be a genetic link. It has been suggested that a subdivided papilla produced divided hairs or that multiple hairs may be due to the partial merging of several papillae. Other possibility is the reactivation of silent embryonic epithelial germs result in multigeminate hairs.[13]

An extensive presentation of pili multigemini over a large area has been previously reported in three patients.[2] They showed a wide patch consisting of irregular and coarse thicker hairs over the entire back. The authors propose that this extensive condition could be underdiagnosed because the nevoid multiple hairs have no specific symptoms.

Diagnosis of pili multigemini is visual. Trichoscopy enhances the evaluation of hair disorders and facilitates the diagnosis of this rare hair shaft dysplasia.[7] Differential diagnosis includes mainly pili bifurcate, which is characterized by bifurcation of the hair shaft. Two features define this dysplasia. Each bifurcation produces two separate parallel branches, which fuse again to form a single shaft, and each branch of the successive bifurcations is covered with its own cuticle.[8] However, in pili gemini, a kinetic papilla splits at the upper end from single to double-tipped during the anagen phase and consequently the same follicular matrix produces two different-sized hair shafts having separate cuticles that emerge through a single pilary canal. Pili gemini maintains the double tipped papilla and consequently the hair shaft does not fuse again.

In conclusion, we present an extensive case of pili multigemini over the back. This condition has been described previously as the nevoid pili multigemini. Despite the rarity of this entity, probably it could be a commonly recognizable condition with an exhaustive exploration. The large areas implicated in the patients described and the normal hair appearance in other locations suggests a genetic link.