Polarized transilluminating dermoscopy: Bedside trichoscopic diagnosis of trichothiodystrophy

Abstract

Trichothiodystrophy is a rare autosomal recessive disorder resulting in a broad range of systemic abnormalities. Polarizing microscopy of the hair reveals the pathognomic "tiger tail" of alternating light and dark bands, but the need for a microscope prevents rapid bedside diagnosis. We describe a new technique for the bedside diagnosis of trichothiodystrophy using a handheld polarizing dermatoscope, precluding the need for microscopic examination. that encode a helicase subunit of transcription/repair factor TFIIH.Mutations in C7ORF11, RNF113A, and GTF2E2 result in similar conditions without photosensitivity. 2 In all mutations, low sulfur levels in the hair shaft cause structural abnormalities. With polarizing light microscopy, distinct "tiger tail" banding, consisting of alternating light and dark bands, are seen that are pathognomonic for the disorder. Trichoscopy, dermoscopic analysis of hair, has been used in the diagnosis of multiple hair shaft disorders, including monilethrix, trichorrhexis invaginata, pili torti, woolly hair, and pili annulati, 4 but TTD cannot be diagnosed using simple trichoscopy. Nonspecific surface abnormalities have been reported that may aid in selecting hairs for closer analysis. 5 We describe new methods for the bedside trichoscopic diagnosis of TTD. | CASE REPORTA 2-year-old girl presented with ichthyosis and neurologic decline.Her gestation had been complicated by preeclampsia, resulting in induced delivery at 31 weeks. She was erythrodermic at birth, which self-resolved. She subsequently demonstrated significant delays in growth and cognitive development, ataxia, coarse ichthyosis of the back, and brittle, short hair with periods of significant hair loss.Funduscopic examination was normal. | METHODSTo assess her hair rapidly for TTD, we developed two techniques to mimic polarizing microscopy that we call polarized transilluminating dermoscopy. Hairs with surface irregularities seen using normal in vivo dermoscopy were clipped and placed on a glass slide. 5 In the first method, a light-emitting diode from a cellular telephone was projected through a polarizing dermatoscope to create polarized light (intensity adjusted using tissue paper). After placing the specimen for transillumination, a second polarizing dermatoscope was then used to view the hair sample ( Figure 1A).In the second method, the specimen was placed on a mirror.When simply viewing the specimen using a polarizing dermatoscope, polarizing light reflects off the mirror to transilluminate the target ( Figure 1B).In contrast to simple trichoscopy using a polarizing dermatoscope (Figure 2A), polarizing transilluminating trichoscopy revealed distinct light and dark bands characteristic of trichothiodystrophy ( Figure 2B, C).

Genetic Hair Disorders: A Review

“…Light microscopy will show trichoschisis (transverse fracture through the hair shaft) with or without trichorrhexisis nodosa [80]. Both trichoschisis and alternating light and dark bands (tiger tail) are visible under polarized light [81].…”

Recent developments in dermoscopy for dermatology

“…Polarized transilluminating dermoscopy (PTD) described by Yang and colleagues is a new technology that combines the features of handheld dermoscopy and polarizing microscopy used for the diagnosis of trichothiodystrophy (TTD). 26 For TTD, polarizing microscopes used by pathologists are the primary diagnostic method and reveal characteristic alternate dark and white bands of the hair shaft with a tiger-tail appearance. 27 The polarizing microscope is a simple device but not always available to dermatologists.…”

Neonatal ichthyosis and hypotrichosis

“…Tiger tail banding with polarized light is characteristic of TTD and is not seen in xeroderma pigmentosum patients . This banding cannot be seen with single polarized dermoscopy, but Yang et al have described a method with two dermatoscopes or one dermatoscope and a mirror. In TTD, trichoscopy shows a nonspecific pattern of sand grains within the hair shaft …”