The different faces of pili bifurcati. A review

ARTICLE

Although Hurwitz said that pili gemini and pili bifurcati are different disorders that should not be confused [1], others [2-4], as well as one of us [5], believe that pili bifurcati represents a restricted form of pili gemini, but with a common pathogenesis. This is the reason why we describe both hair shaft dysplasias together and discuss a new classification (Fig. 1).

Pili gemini and pili multigemini

"Pili multigemini" is characterized by groups of different-sized hairs with their own cuticle, that grow from the same follicular matrix and emerge through a single pilary canal. The hair shafts have their own cuticle. The name was proposed by Pinkus in 1951 [6], who indicated that two to eight shafts may grow from a single follicular matrix and papilla, the upper end of which is split into tips that correspond one-to-one with each hair shaft. When there is only one bifurcation of the papilla or matrix, two hair shafts emerge through the pilary canal; this must be named "pili gemini". When there are several splits, many hair shafts are noted through the same pilary canal, and the dysplasia should be called "pili multigemini" since the papilla divided several times.

The pathogenesis of this dysplasia is as follows: during the anagen phase, a kinetic dermal papilla changes its form from single-tipped to double-tipped producing two hair shafts that emerge separately through the same pilary canal (Fig. 2). This process is very common, and may be observed both in other dysplasias and in normal hair. It has been reported as occurring in cleidocranial dysostosis [7] and in the trichorinophalangeal syndrome [8]. Less frequently, the papilla splits into four or eight tips producing four to eight subpapillae which will produce 4 to 8 hair shafts that emerge separately from the pilary canal. "Pili multigemini" is rare in daily practice, and when we clinically find several hair shafts emerging from the same pilary canal we must consider a differential diagnosis of "trichostasis spinulosa" [9].

Pili bifurcati and multibifurcati

"Pili bifurcati" was described by Weary et al. in 1973 [10] in a 3-year-old boy. This uncommon developmental defect of the hair growth is characterized by intermittent bifurcation of the whole hair shaft at irregular intervals [11]. Each bifurcation produces two separate parallel branches which fuse again to form a single shaft. Each branch of the successive bifurcations has its own cuticle, which surrounds it completely [12]. The anomaly appears to be transitory, with only a small percentage of hair exhibiting the bifurcation [1]. Clinically, the patient may show a diffuse alopecia, more evident in some areas, similar to trichotillomania or pili torti [2, 12].

The pathogenesis of this dysplasia is as follows: during the anagen phase, the matrix-papilla changes its form from single-tipped to double-tipped, then back to single-tipped again; consequently, a single hair shaft is produced, then a bifurcated hair shaft, and then a single hair shaft again. Each branch has its own cuticle and they are of different diameter. This dysplasia should be named "pili bifurcati" (Fig. 3).

This process is uncommon, and occurs in normal hair and in pili canaliculi and monilethrix. It was also described in association with the mosaic trisomy 8 syndrome [13].

If the matrix-papilla changes its shape several times during the anagen phase, it produces hairs with bifurcations at irregular intervals. As in the previous situation, each branch of sucessive bifurcations has its own cuticle, which surrounds it completely. This dysplasia should be named "pili multibifurcati" (Fig. 4).

This dysplasia is very uncommon and has been seen only twice by one of us (FC) in cases secondary to protein deficiency. The first patient had ulcerative colitis [14], the second had undergone an extensive bowel resection. In these cases of "high-quality protein deficiency" [15], after telogen effluvium, the follicular matrix-papilla has to produce a new hair shaft. During this new anagen phase, the kinetic matrix-papilla could divide into two, to produce a bifurcated hair. This would later, when again deprived of good quality protein, transform into a single matrix-papilla. Afterwards, on recovery, this would again subdivide, and so on, thus showing intermittent bifurcations.

Pili bi, bifurcati

It is even possible that the same matrix-papilla which was already divided, might again subdivide, leading to a bifurcation of the already bifurcated branch. Each new branch has its own cuticle, which surrounds it completely, and as in the single bifurcation the branches will be of different size or diameter. Finally the branches of the second bifurcation fuse again, and afterwards the first bifurcated branches fuse again. This disorder can be named "pili bi, bifurcati" (Fig. 5). It is extremely uncommon, and was described in a four-year old boy with alopecia in a large area of his occipital region [16].

Although an autosomal recessive inheritance was proposed, this mode of transmission cannot be taken as certain [17].

Pili bifurcati vs central trichoptilosis

This form is not true pili bifurcati since split sections are not surrounded by cuticle. It should be called "central trichoptilosis". Nevertheless, it has been shown in several trichological studies, generally associated with other hair shaft dysplasias [18, 19], and it was named "pseudopili bifurcati". All of us have seen this disorder in several dysplasias, and also in trichonodosis in normal hair with knots produced by mechanical or physical forces (Fig. 6) [20].

Since it is absolutely different from "pili bifurcati" because it is produced as a consequence of a trauma to the hair shaft, resulting in splitting with two parts that are, when taken separately, never surrounded by a complete cuticula, and the cortex and medulla may be broken, and, in addition there are no changes in the matrix-papilla, the names "pseudo pili bifurcati", "acquired pili bifurcati" or "iatrogenic pili bifurcati" must be avoided and changed to "central trichoptilosis". In conclusion, as it is not true pili bifurcati, our proposal is that this form should not be considered in this group of disorders.

Why pili bifurcati?

Although we admitted that the bifurcations of pili bifurcati are a consequence of splits of the follicular germen, and consequently that "pili bifurcati" would be the result of the "pili gemini", this "terminology" must not be applied to all the forms of pili bifurcati. In addition, normally the diagnosis is by trichogram, in other words, on the hair shaft or "pili" and not by biopsy or on the matrix-papilla (germen).

But we must use both terms to define different disorders. Pili gemini should be used to define situations in which the matrix-papilla is split producing two different branches (pili gemini) or four to eight different branches (pili multigemini) that do not fuse again since they remain separate and independent permanently. Pili bifurcati would be used when the different sized branches fuse again, once (pili bifurcati), several times (pili multibifurcati), and once again on a previously bifurcated branch (pili bi, bifurcati), independently so that the kinetic matrix-papilla must be transformed again from two into one papilla. In "central trichoptilosis", there is no splitting of the matrix and papilla and there are no true bifurcations. Hence, this acquired condition should be clearly separated from pili gemini and pili bifurcati.

In accordance with these concepts, we consider that our previous classification [14, 16] must be modified (Table I).

CONCLUSION

This paper was presented to the VIth Congress of the European Academy of Dermatology and Venereology, Dublin, 11-15 September, 1997.

This article was prepared in the Trichology Unit of the Virgen Macarena Universitary Hospital (Seville, Spain) with the collaboration of the Department of Dermatology of Marburg (Prof. R.Happle), Department of Dermatology of Bologna (Prof. A.Tosti) and Departments of Dermatology and Pediatrics of Dallas (Prof. D.Whiting).

Article accepted on 3/3/00

REFERENCES

1. Hurwitz S. Disorders of hair and nails. In: Hurwitz S (ed). Clinical Pediatric Dermatology. 2nd ed., Philadelphia, W.B. Saunders Co., 1993: 481-514.

2. Whiting DA. Structural abnormalities of the hair shaft. J Am Acad Dermatol 1987; 16: 1-25.

3. Rook AJ, Dawber RPR. Defects of the hair shaft. In: Rook A, Dawber RPR (eds). Diseases of the hair and scalp. 2nd ed. London, Blackwell Sci. Pub. 1991; 200-55.

4. Price V. Structural anomalies of the hair shaft. In: Orfanos CE, Happle R (eds). Hair and hair diseases. Berlin, Springer-Verlag Ed, 1990; 363-422.

5. Camacho F. Hair shaft dysplasias. General concept and classification of the dysplasias. In: Camacho F and Montagna W (eds), Trichology. Diseases of the pilosebaceus follicle. Madrid. Biblioteca Aula Médica Ed, 1997; 181-202.

6. Pinkus H. Multiple hairs (Flemming-Giovannini): report of two cases of pili multigemini and discussion of some other anomalies of the pilary complex. J Invest Dermatol 1951; 17: 291-301.

7. Mehregan AH, Thompson WS. Pili multigemini. Report of a case in association with cleidocranial dysostosis. Br J Dermatol 1979; 100: 315-22.

8. Camacho F, Armijo M, Naranjo R, Dulanto F. Le syndrome tricho-rhino-phalangien (Giedion). Ann Dermatol Vénéréol 1978; 105: 17-21.

9. Braun-Falco O, Vakilzadeh F. Trichostasis spinulosa. Hautarzt 1967; 18: 501-4.

10. Weary PE, Hendricks AA, Warner F, Ajgaonkar G. Pili bifurcati: new anomaly of hair growth. Arch Dermatol 1973; 108: 403-7.

11. Camacho F, Montagna W. Displasias pilosas (Anomalías del tallo piloso). En Camacho F, Montagna W (eds), Tricología. Madrid, Garsi Ed. 1982; 91-103.

12. Camacho F, Ferrando J. Hair shaft dysplasias. Int J Dermatol 1988; 27: 71-80.

13. Breslau-Siderius LJ, Beemer FA, Boom BW. Pili bifurcati occurring in association with the mosaic trisomy 8 syndrome. Clin Dysmorphol 1996; 5: 275-7.

14. Camacho FM. Pili bifurcati in a woman with ulcerative colitis. Eur J Dermatol 1996; 6: 355-6.

15. Melnikoff GM. Temporary reddening of the hair in ulcerative colitis. Am J Digest Dis 1957; 2: 738-40.

16. Camacho F, Jorquera E. Pili bi, bifurcati. Eur J Dermatol 1995; 5: 88-9.

17. Happle R. Genetic defects involving the hair. In: Orfanos C, Happle R (eds). Hair and Hair diseases. Berlin, Springer-Verlag Ed, 1999; 325-62.

18. Sala F, Crosti C, Bencini PL, Menni S. An unusual defect resembling "pili bifurcati". Arch Dermatol 1985; 121: 718.

19. Sala F, Crosti C, Bencini PL, Mansi M, Greppi F, Perotta E, Andreani B. Pseudo "pili bifurcati": aspett microscopici ed ultrastrutturali. Giorn It Derm Vener 1987; 122: 371-3.

20. Camacho F, Muñoz MA. The multiple faces of trichonodosis. In Van Neste D, Randall VA (eds), Hair research for the next millennium. Amsterdam, Elsevier Ed, 1996; 51-3.