Trichoscopy by using a videodermoscope or handheld dermoscope can enhance the clinical diagnosis of various hair and scalp diseases123. In recent years, the handheld-type dermoscope has been considered a reliable, easy-to-use device as shown by its comparable results to those of videodermoscopes456789. Trichoscopic findings of hair loss have been well described for the differential diagnosis of alopecia; however, most previous studies were primarily performed in Caucasian patients. Therefore, we performed this study to find any distinct pattern in the trichoscopic findings of normal persons and patients with alopecia due to various causes in Korean, and analyzed the trichoscopic patterns to verify any relation with known predisposing findings reported earlier in Caucasian alopecia patients.

The diagnosis and demographic profiles of the patients in this study are shown in Table 2.

As shown in this observation, some distinct trichoscopic patterns are predominant in certain types of alopecia, and this aids in predicting the correct diagnosis. However, the interpretation of trichoscopic findings should be done carefully because a pigmented pattern of the scalp can be influenced by several factors, including the light type of dermoscope, hair-washing habit, use of hair dye or camouflage products (dark makeup powder or foundation, cosmetic hair fibers), as well as the skin type and hair color. Koreans, or the northern Mongoloids, have distinct skin and hair characteristics such as yellow or light brown skin, and straight and black hair that is coarse with a thicker diameter and lower density compared with Caucasoid hair. Thus, there are some differences in trichoscopic findings of the scalp and hair between Koreans and Caucasians. We examined the frequency of various trichoscopic findings of normal persons and alopecia patients from the Korean population, because most of the previous studies were primarily performed in Caucasian patients, with a few others in Japanese patients7910. Although a previous trichoscopic study in Koreans has been reported, the observation was rather confined to localized hairless patches in a cross-sectional study with a restrictive statistical analysis of only 14 trichoscopic features as discriminative variables, and without a normal control group11. In this study, we extended the distinctive trichoscopic features to 35, consisting of the 31 previously known trichoscopic features and 4 new trichoscopic features that could be characteristic or helpful in the diagnosis of both localized and diffuse alopecia, and we compared them with normal control subjects through an appropriate statistical analysis.

In the present study, there were no specific trichoscopic findings confined to the normal scalp, although simple red loops were more common. In addition, the frequency of pinpoint white dots, perifollicular scales, dirty dots, and uniform thinning did not show a significant difference between the normal and alopecia groups. Therefore, these five features could be considered nonspecific or of no diagnostic significance when they are shown independently. Some trichoscopic findings showed a unique distribution and prevalence rate depending on age. Unlike in an earlier study by Fu et al.12, dirty dots, nonmicrobial environmental particles appearing as brown and black particulate dots or loose fibers, revealed a bimodal peak distribution and were predominantly seen in children (<10 years old) and older patients (>60 years old). We considered that the decreased sebaceous activity resulting from the immature and regressed sebaceous glands in these age groups may affect inability to eliminate the environmental particles. Uniform thinning, empty follicles, and short vellus hairs were predominantly seen in the older group, a pattern that seems to reflect a normal physiologic aging process.

Several reports supporting the value of trichoscopy in the differential diagnosis of localized hair loss have been published. Yellow dots, black dots, broken hairs, exclamation mark hairs, and short vellus hairs in AA; broken hairs with different lengths in TM; comma hairs and corkscrew hairs in TC; and diffuse white areas in PCA were shown to be hallmark features in a previous study101314151617. However, in our observation, black dots, broken hairs, and short vellus hairs were variably encountered in all types of localized noncicatricial alopecia; thus, seem to have less diagnostic value especially in the differential diagnosis of localized noncicatricial alopecia. On the other hand, the following trichoscopic features were significantly more common in particular types of localized noncicatricial alopecia, which are thought to be valuable characteristic features: yellow dots, exclamation mark hairs, proximal tapering hairs in AA, trichoptilosis and pointed hairs in TM, and corkscrew hairs, septate hyphae, and comma hairs in TC. Although exclamation mark hairs and yellow dots were known as hallmark features of AA in an earlier study, those features also appeared with a similar frequency in the TM and TA groups, respectively. Interestingly, proximal tapering hairs were observed only in AA; therefore, this could be considered as a pathognomonic feature of AA. Proximal tapering hairs, long elongated hair shafts that are narrowed down to the follicles without breakage, are different from short broken exclamation mark hairs in that their distal ends are not visible within the field of the dermoscopic view. A tapering hair alone may often be confused with a normal short regrowing hair with a distal tip; therefore, the term "proximal tapering hair" indicates its overall shape rather than tapering. Trichoptilosis and the pointed hairs of TM were also valuable characteristic features, but were not absolutely diagnostic. Pointed hairs, named by us in this study, are a kind of short broken hairs (<5 mm) that particularly look like a "bayonet" with artificially tapered, ragged distal tip predominantly in lower magnification. We consider that it may be analogous to the distal longitudinal splitting of the hair shaft resulting from mechanical manipulations. In TC, comma hairs, corkscrew hairs, and septate hyphae hairs (hair shafts divided into compartments separated by fungi) seem to be specific markers in this study. Comma hairs are short, bent, comma- shaped hairs with homogeneous thickness and share a diagonal end. Corkscrew hairs, broken hairs showing a spiral shape, differ from comma hairs with the presence of multiple twists and intensively coiled appearance. Septate hyphae hairs, also known as Morse code-like hairs, show multiple transverse white bands across the hair shaft. Although the trichoscopic findings of TC in relation to clinical and mycological features remain unclear, completely broken comma hairs or partially broken corkscrew/ septate hyphae hairs are probably associated with the severity of, or different types of fungal infection (i.e., endothrix or ectothrix). Although arborizing vessels and short vellus hairs were more common in TA than in other alopecia groups, they do not seem to be specific features; therefore, a detailed history can be very important in diagnosing TA. Diffuse white areas and fibrotic white dots, related to scar formation, were prominent features of PCA, which is similar to previous results; however, these features can also be seen in some cases of longstanding TA and AA18. In addition to scarring features, a predominance of single hairs, perifollicular erythema, pustules, follicular hyperkeratosis, pili torti, and tufted hairs, which are observed predominantly on the periphery of active lesions, were more common in the PCA group; therefore, they can be helpful in distinguishing PCA from other forms of localized alopecia. Among them, tufted hairs are thought be a diagnostic feature of PCA.

Trichoscopic findings of diffuse hair loss have not been investigated extensively in comparison with those of localized hair loss. Most of the previous studies were performed with a videodermoscope with a high magnification, and there have been insufficient comparative studies123. Hair diameter diversity (≥20%) and the peripilar sign are important distinguishing features of AGA19202122; however, there are no established sensitivities or specific clues for the diagnosis of TE122. In nonbald AA incognita, which can be easily confused with AGA or TE, yellow dots and short regrowing hairs are known as the characteristic features2324. In this study, the overall trichoscopic pattern of diffuse AA was similar to that seen in localized AA, with a higher prevalence rate of black dots, short vellus hairs, broken hairs, yellow dots, and exclamation mark hairs. Proximal tapering hairs and exclamation mark hairs are considered the most specific features of AA for the differential diagnosis of diffuse alopecia. In addition to hair diameter diversity and peripilar sign, a predominance of single hairs and uniform thinning (defined as ≥80% thin hairs in one trichoscopic fieldview) were also distinguishing features of AGA in this study. In TE, a group of short nonvellus hairs, newly emerging just above surface of the scalp, were the most commonly observed finding. Short nonvellus hairs are also short and thin, but differ from short vellus hairs by their firm appearance with intense pigmentation, pointed distal end, and upright position. Perifollicular scales and simple red loops were also more common in the TE group compared with other types of diffuse alopecia, although those findings were observed on the normal scalp. Therefore, trichoscopic features can help distinguish TE from other forms of diffuse hair loss such as AGA.

The common or critical trichoscopic findings in this study for the differential diagnosis of alopecia, with regard to the follicular, perifollicular, hair shaft, and vascular patterns, revealed similarities to earlier studies primarily done in Caucasians (Table 6)1389141920. Arborizing vessels and dirty dots in normal scalp (19.7% and 8.8% vs. 25.7%~26.6% and 11.1%); broken hairs in AA, TM, and TC (59.9%, 100.0%, and 100.0% vs. 57.1%~67.0%, 100.0%, and 83.0%); and exclamation mark hairs in AA (41.3% vs. 42.9%~71.0%) were relatively shown to have similar frequencies compared with Caucasians. However, the pigmentation patterns (i.e., peripilar signs, honeycomb pigment network, yellow dots, pinpoint white dots, and fibrotic white dots) and hair shaft patterns such as black dots and short vellus hairs were significantly different between Caucasians and Koreans. The incidence of the peripilar sign and honeycomb pigment network in AGA, and yellow dots in both AA and AGA was 31.6% and 19.7%, 55.7% and 11.8%, respectively, which are lower than those in Caucasians (59.3%~100.0% and 18.7%~37.3%, 66.0%~95.0% and 8.0%~66.0%, respectively). This may be influenced by the concealing light effect of the Asian skin color, with its yellow or brown pigmentation, which makes these features more difficult to detect591923242526. In contrast, light-colored pinpoint white dots in normal scalp (13.1% vs. 0%); short vellus hairs in AA (62.3% vs. 27.1%~53.0%); black dots in AA, TM, and TC (77.8%, 100.0%, 77.8% vs. 53.3%~63.3%, 27.0%, 25.0%); and fibrotic white dots in PCA (70.6% vs. 52.4%) were more frequently observed in Koreans in comparison with Caucasians9. This is also thought to be the result of the light contrast effects between the hypopigmented pattern and darker background color of the skin. Contrary to our expectations, the frequencies of the remaining features, such as simple red loop, perifollicular scales, trichoptilosis, comma hairs, corkscrew hairs, and tufted hairs, also appeared differently from previous studies on Caucasians. This could be influenced by several factors, including the type of light and magnification of the dermoscope, hair-washing habit, and the subtype or severity of each alopecia group, but not by racial difference.

Yet, our study also bears several limitations. First, the progressive acute AA to totalis/universalis patients may be categorized into the diffuse type during the early stage of examination. Second, the stage and disease duration of TE patients were somewhat diverse because of causative factors that were not considered thoroughly in this study.

Third, more cases need to be analyzed to obtain higher statistical power. Therefore, additional well-designed prospective studies with more alopecia patients are necessary to draw a conclusion regarding this subject. In conclusion, we identified some distinct trichoscopic patterns of localized and diffuse alopecia patients and normal persons in Korean. Most of the critical trichoscopic features of Korean alopecia patients are similar to those of Caucasian patients; however, racial difference must be considered in some pigmentation patterns that may vary compared with Caucasians.