Correlation of trichoscopy (hair and scalp dermoscopy)
Trichoscopy is the dermoscopic study of inflammatory, infectious and artefactual hair and scalp disorders. It can help in the diagnosis and follow-up of these diseases (Richarz et al., 2018; Tosti, 2007) and to guide the biopsy procedure, allowing identification of even individually affected hair follicles (Miteva and Tosti, 2013). Trichoscopic structures or patterns can be specific to a certain scalp disorder, although some of them can be found in diverse hair and scalp diseases (Mubki et al., 2014; Rossi et al., 2015) (table 10).
Pigment pattern
The pigment pattern is a pseudonetwork composed of brown lines and holes. Histolopathologically, lines correspond to pigmented rete ridges (Tosti, 2015).
Yellow dots
Yellow dots are round yellowish to pinkish structures. Histologically, they correspond to a distended follicular infundibulum plugged with keratin and sebum (Tosti, 2007). Yellow dots are characteristic of alopecia areata (AA), although can be seen in androgenetic alopecia and other scalp disorders (Rossi et al., 2015; Waśkiel et al., 2018).
Black dots
Black dots (“cadaverized hairs”) are round dark structures inside the follicular ostia. Histopathologically, they reveal stubs of hairs that are fractured before their emergence from the scalp. Black dots are seen in AA and are a sign of disease activity (Jain et al., 2013; Miteva and Tosti, 2012).
Pinpoint white dots
Pinpoint white dots are small round whitish structures. Histologically, they correspond to follicular and sweat gland openings, and are seen in normal scalp and in all types of alopecia (Lacarrubba et al., 2015).
White patches
White patches are large and irregular pale structures. Histologically, they represent destroyed follicles replaced by fibrous tracts and focal absence of melanin (Kossard and Zagarella, 1993). White dots are seen in cicatricial alopecia.
Blue-gray dots
Blue-gray dots are round grayish structures. They can present as a target pattern or as a speckled pattern. Blue-gray correspond to the presence melanophages in dermis. The target pattern is due to the presence of melanin around the hair follicle, and is observed in lichen planus pilaris (LPP). The speckled pattern is secondary to the presence of melanin in interfollicular areas and is seen in discoid lupus erythematosus (Ankad et al., 2013; Rossi et al., 2015).
Empty Follicles.
Empty follicles are seen dermocopically as skin-colored small depressions without hairs. They correspond to an empty infundibula (Jain et al., 2013).
Absence of Follicular Opening
No hair follicles are seen with dermocopy. It reveals dermal fibrosis and is characteristic of scarring alopecia (Tosti, 2015).
Peripilar Casts
Peripilar hair casts are concentrically arranged scales surrounding the hair shaft. Histologically, they correspond to perifollicular inflammation. They are frequently seen in LPP, although they can be present in other scarring alopecias and in keratinization disorders (Mubki et al., 2014; Tosti, 2015).
Peripilar Sign
The Peripilar sign is a brown halo surrounding the follicular ostium. Histopathologically, it reveals perifollicular inflammation. The Peripilar sign is often seen in androgenetic alopecia (Mubki et al., 2014).
Follicular Keratotic Plugging
Follicular keratotic plugs are yellow-brownish round structures, larger than dots (Mubki et al., 2014). Histologically, they reveal hyperkeratosis and keratin material occluding dilated infundibular openings (Rossi et al., 2015).
Histologic correlation in trichoscopy
| Trichoscopy and description | Histologic correlation | Associated disorders |
| Pigment pattern or honeycomb pattern
Meshwork composed of brown lines and holes |
Lines correspond to pigmented rete ridges | Ultraviolet exposure |
| Yellow dots
round yellowish to pinkish structures |
Distended follicular infundibulum plugged with keratin and sebum | Alopecia areata
Androgenetic alopecia |
| Black Dots
Round dark structures (“cadaverized hairs”) |
Stubs of hairs that are fractured before their emergence from the scalp | Alopecia areata |
| Red dots
Round red structures, regularly distributed around follicular openings |
Widened follicular ostia surrounded by dilated vessels | Discoid lupus erythematosus |
| Pinpoint white dots
Small round whitish structures |
Follicular and sweat gland openings | Normal scalp and all types of alopecia |
| White patches
large and irregular pale structures |
Destroyed follicles replaced, dermal fibrosis and focal absence of melanin | Cicatricial alopecia |
| Blue-gray dots
Round grayish structures Target pattern Speckled pattern |
Presence of melanophages in dermis
Melanin around the hair follicle. Pigmentary incontinence restricted to the follicular units Melanin in interfollicular areas |
Lichen planus pilaris Discoid lupus erythematosus |
| Empty Follicles
Skin-colored small depressions without hairs |
Empty infundibula | Alopecia areata
Androgenetic alopecia Telogen effluvium |
| Absence of Follicular Opening | Dermal fibrosis | Cicatricial alopecia |
| Peripilar Casts
Concentrically arranged scales surrounding the hair shaft |
Inflammation in perifollicular area | Lichen planus pilaris
Frontal fibrosing alopecia Keratinizing disorders |
| Follicular Keratotic Plugging
Keratotic masses plugging follicular openings |
Hyperkeratosis and keratin material occluding dilated infundibular openings | Discoid lupus erythematosus |
