Aqcuired nonscarring alopecia
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Androgenetic alopecia is characterized by predominance of trichoscopic abnormalities in the frontal area compared to the occipital area . The progressive miniaturization of hair follicles is observed in trichoscopyThis glossary term has not yet been described. as hair shaft thickness heterogenity (more than 20% of observed hair shafts are thinner that terminal hair shafts  and increased proportion of thin and vellus hairs (higher than 10%). Moreover, there is a tendency to observe follicular units with one or two hairs instead of predominance of follicular units with three or more hairs.  Other trichoscopic features are: presence of variable number of yellow dots and perifollicular discoloration (hyperpigmentation, peripilar sign) 
Diagnostic trichoscopic criteriameasure of how well one variable or set of variables predicts an outcome for female androgenetic alopecia :
Fulfillment of two major criteria or one major and two minor criteria is required to diagnose female androgenetic alopecia.
Trichoscopic findings of alopecia areata include black dotsDots are small, round structures of less than 0.1 mm in diameter that have a red color when corresponding to blood vessels; however, when due to melanin, their color ranges from black, brown, to blue-gray depending on the depth and concentration of the melanin in the skin (Tyndall effect)., broken hairs, exclamation mark hairs, tapered hairs, Pohl-Pinkus constrictions, yellow dots, short vellus hairs, upright regrowing hairs and pigtail hairs .
|Trichoscopic feature||Reported prevalence in %* (mean value**)|
|Yellow dots||6 - 100 (62)|
|Black dots||0 - 84 (53)|
|Exclamation mark hairs||12 - 71 (39)|
|Tapered hairs||5 - 81 (51)|
|Broken hairs||0 - 71 (49)|
|Short vellus hairs||34 - 100 (61)|
|Upright regrowing hairs||11 - 96 (23)|
|Pigtail (circle) hairs||4 - 61 (21)|
|Pohl-Pinkus constrictions||2 - 10 (4)|
Good response to the therapy of alopecia areata is characterized the reduction followed by the loss of exclamation mark hairs, broken hairs and black dots . Yellow dots are the least responsive . In initial hair regrowth, increased number of short vellus hairs is observed. With the continuation of the therapy they are substituted by fully pigmented terminal hairs so a decreased number of short vellus hairs may be detected . Hair regrowth is characterized by presence of upright regrowing hairs and pigtail hairs .
Active hair loss in alopecia areata is characterized by presence of black dots, broken hairs, exclamation mark hairs, tapered hairs and Pohl-Pinkus constrictions [6, 7]   . In long-lasting, non-active disease mainly yellow dots and short vellus hairs are observed .
TrichoscopyThis glossary term has not yet been described. of trichotillomania is characterized by presence of hairs broken at different length, black dots, trichoptilosis, coiled hairs, flame hairs, V-sign and tulip hairs .
There are no specific trichoscopy findings of telogen effluvium . However, presence of upright regrowing hairs and predominance of single-hair follicular units with perifollicular discoloration may be indicative of telogen effluvium in absence of features characteristic for other causes of hair loss .
1. Rakowska, A., et al., DermoscopyThe examination of [skin lesions] with a 'dermatoscope'. This traditionally consists of a magnifier (typically x10), a non-polarised light source, a transparent plate and a liquid medium between the instrument and the skin, and allows inspection of skin lesions unobstructed by skin surface reflections. Modern dermatoscopes dispense with the use of liquid medium and instead use polarised light to cancel out skin surface reflections. in female androgenic alopecia: method standardization and diagnostic criteria. Int J Trichology, 2009. 1(2): p. 123-30.
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3. Blume-Peytavi, U., et al., S1 guideline for diagnostic evaluation in androgenetic alopecia in men, women and adolescents. Br J Dermatol, 2011. 164(1): p. 5-15.
4. Rudnicka, L., et al., Trichoscopy update 2011. J Dermatol Case Rep, 2011. 5(4): p. 82-8.
5. Waskiel, A., et al., Trichoscopy of alopecia areata: An update. J Dermatol, 2018.
6. Guttikonda, A.S., et al., Evaluation of Clinical Significance of Dermoscopy in Alopecia Areata. Indian J Dermatol, 2016. 61(6): p. 628-633.
7. Inui, S., et al., Clinical significance of dermoscopyThe examination of [skin lesions] with a 'dermatoscope'. This traditionally consists of a magnifier (typically x10), a non-polarised light source, a transparent plate and a liquid medium between the instrument and the skin, and allows inspection of skin lesions unobstructed by skin surface reflections. Modern dermatoscopes dispense with the use of liquid medium and instead use polarised light to cancel out skin surface reflections. in alopecia areata: analysis of 300 cases. Int J Dermatol, 2008. 47(7): p. 688-93.
8. Kibar, M., et al., Trichoscopic findings in alopecia areata and their relation to disease activity, severity and clinical subtype in Turkish patients. Australas J Dermatol, 2015. 56(1): p. e1-6.
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10. Rudnicka, L., M. Olszewska, and A. Rakowska, Atlas of trichoscopy: dermoscopy in hair and scalp disease. 2012, London: Springer.
11. Ganjoo, S. and D.M. Thappa, Dermoscopic evaluation of therapeutic response to an intralesional corticosteroid in the treatment of alopecia areata. Indian J Dermatol Venereol Leprol, 2013. 79(3): p. 408-17.
12. El Taieb, M.A., et al., Platelets rich plasma versus minoxidil 5% in treatment of alopecia areata: A trichoscopic evaluation. Dermatol Ther, 2017. 30(1).
13. Rakowska, A., et al., New trichoscopy findings in trichotillomania: flame hairs, V-sign, hook hairs, hair powder, tulip hairs. Acta Derm Venereol, 2014. 94(3): p. 303-6.
14. Kowalska-Oledzka, E., et al., 'Black dots' seen under trichoscopy are not specific for alopecia areata. Clin Exp Dermatol, 2012. 37(6): p. 615-9.