The mother of a healthy 21-month-old girl says that her daughter's unruly hair never lies flat on the scalp and cannot be tamed by combing or brushing.
Diagnosis:Uncombable hair syndrome (pili trianguli et canaliculi)
Uncombable hair syndrome (UHS), or "spun-glass hair," is characterized as frizzy, dry, silvery-blond to straw-colored hair that stands away from the scalp and is unable to be combed flat.1,2 Only scalp hair is affected, and eyelash, eyebrow, facial, and body hair is normal in appearance.3 The entire scalp typically is involved, but localized forms have occurred in some persons.1,3 A person's degree of disarray may be related to the number of hairs affected, and approximately 50% of hairs must be affected for clinical changes to become apparent. The quantity, fragility, and rate of hair growth are normal.3,4 The syndrome is not associated with any physical, mental, or neurologic abnormalities.1-5 UHS usually becomes evident between 3 months to 3 years of age but can present at any time from infancy to 12 years.1 It is rare, with fewer than 100 reported cases.
Most cases of UHS are inherited in an autosomal-dominant manner, with either complete or incomplete penetrance, but autosomal recessive and sporadic forms of inheritance have been reported.1
The pathogenesis of UHS is unclear.2 In general, the shape of the inner root sheath establishes the shape and surface of the hair shaft by acting as a rigid structure.1 It is thought that a misshapen dermal papilla alters the shape of the inner root sheath. Subsequently, the inner root sheath prematurely keratinizes before the central-forming hair, causing focal asymmetry of the hair bulb and lateral loss of hair matrix.1,3 These abnormalities manifest as a lateral longitudinal groove along the hair shaft. As a result, the hair shaft irregularly twists along its axis at regular intervals, preventing adjacent hair shafts from grouping together in locks, making it extremely difficult to comb.1
Diagnosis can be confirmed using scanning electron microscopy (SEM) in which the longitudinal grooves along the hair shaft are readily identified.3,4 Moreover, SEM examination of a cross section of a characteristic hair shaft often reveals that it is triangular, reniform, or heart-shaped in contrast to the normal round to oval outline. To make the diagnosis of uncombable hair syndrome, at least 50% of hairs must be affected, because longitudinal grooves are present in 5% of hairs in the general population.3
Treatment is limited.2 Most persons with UHS note improved manageability by adolescence.1-5 Some cases even spontaneously regress with time.2,4 Hair manageability often improves with increased hair length.2 Gentle hair care is recommended, although its efficacy is subjective.1 Patients should use conditioners and soft brushes and avoid harsh hair treatments such as perms, chemical relaxants, or excessive brushing and blow drying. Biotin 0.3 mg 3 times a day for 4 months produced significant improvement in hair combability in 1 patient.