Dermoscopy’s Hidden Gem: Cross-Polarized Dermoscopy Unveiling Trichothiodystrophy at the Bedside

Dear Editor, Cross-polarized dermoscopy is an innovative imaging technique used as a modification of routine dermoscopy. It allows for enhanced visualization of skin and hair structures by eliminating specular reflection from the skin surface, thereby enabling visualization of deeper structures such as melanin pigment and blood vessels.[1] Cross-polarized dermoscopy can be employed in the diagnosis of certain dermatological conditions including trichothiodystrophy (TTD), which typically requires polarized microscopy, an expensive and less accessible method. Additionally, it can be employed as a simple bedside tool for diagnosing TTD by revealing characteristic alternating light and dark bands along hair shafts, known as 'tiger tail banding'.[2] We describe the case of a pediatric patient presenting with short, sparse, brittle hair since birth. We utilized the principle of cross-polarized dermoscopy using a video-dermoscope and mirror to diagnose TTD. A 4-year-old female patient, born out of a consanguineous marriage, had a history of delayed milestones and presented with short, sparse, and brittle hair since birth [Figure 1]. According to the parents, the child's hair never grew long enough to require a haircut. On examination, the patient had short stature, intellectual impairment, and strabismus in the right eye. Cutaneous examination revealed short, unruly, and brittle scalp hair, eyelashes, and eyebrows. There was no associated photosensitivity or any similar history in the family. The nails and teeth were normal. Hair pull test and hair tug test were positive. Trichoscopy revealed broken hair and trichoschisis [Figure 2a and 2b]. Light microscopy revealed trichoschisis and dystrophic hair root [Figure 2c]. Laboratory parameters and metabolic screening were normal. Using a polarized AM4515ZT Dino-Lite Edge video-dermoscope and a mirror, transillumination of the hair shafts revealed alternating light and dark bands [Figure 2d]. The patient was diagnosed with TTD, a genetic hair shaft disorder.Figure 1: Short sparse unruly hair in a four-year-old female patientFigure 2: (a) Trichoscopy showing trichoschisis (blue arrow); Dinolite AF115ZT, polarized 70x. (b) Light microscopy showing multiple transverse fractures of hair shaft (trichoschisis), 40x. (c) Light microscopy showing dystrophic hair root, 40x. (d) Cross-polarized dermoscopy showing the characteristic 'tiger tail banding' of the hair shaft; Dinolite AF115ZT, polarized 70xCross-polarized dermoscopy involves the use of a mirror and dermoscope to capture polarized light. The process begins by placing a trichogram slide on a mirror, followed by positioning the dermoscope on top. As the polarized light reflects off the mirror, it penetrates through the hair shaft and is subsequently captured by the dermoscope.[3] One of the key advantages of cross-polarized dermoscopy is its ability to reduce surface reflections, thus providing a clearer view of subsurface structures. In the context of TTD, cross-polarized dermoscopy plays a crucial role in the diagnostic process. It offers real-time visualization, allowing immediate assessment of hair shaft disorders at the bedside. This approach is valuable in clinical settings, enabling dermatologists to quickly evaluate TTD-associated features and guide further diagnostic investigations or interventions. Moreover, cross-polarized dermoscopy decreases the necessity for unnecessary biopsies or invasive procedures by providing valuable diagnostic information without additional patient discomfort or risks. Thus, cross-polarized dermoscopy emerges as a valuable, cost-effective, and novel bedside tool for diagnosing hair shaft disorders, specifically TTD, insituations where advanced polarized microscopes are not easily accessible. The technique can be incorporated into the diagnostic algorithm of various hair shaft disorders in addition to the routine trichoscopy and light microscopy. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient's parent/guardian has/have given his/her/their consent for their child's images and other clinical information to be reported in the journal. They understand that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.