this disorder is relatively frequent on the beard of adult men and on the scalp of children .
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 ] .
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 .
( 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 histologic image .
follicular structures include different hair shafts ( yellow arrows ) , which were enclosed in a common outer root sheath
pili multigemini is a hair disorder characterized by clusters of shafts that emerge from a single follicle .
a common bulb encloses a dermal papilla that splits into different - sized hair shafts with separate cuticles .
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 .
an extensive presentation of pili multigemini over a large area has been previously reported in three patients .
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 .
trichoscopy enhances the evaluation of hair disorders and facilitates the diagnosis of this rare hair shaft dysplasia .
differential diagnosis includes mainly pili bifurcate , which is characterized by bifurcation of the hair shaft .
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 .
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 .
 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
CASE REPORT
DISCUSSION