**3.1 Clinical features**

AA presents as circumscribed and smooth patches of non-scarring alopecia. AA can affect any hair-bearing region, including not only the scalp but also eyebrows (**Figure 2a**), eyelashes, beard (**Figure 2b**), and any hair-bearing location. Even when patients are usually asymptomatic, some report a tingling or itchy sensation within the alopecia patches. Course of the disease is unpredictable, but spontaneous hair regrowth is observed in approximately 50% of patients with patchy AA within a year. In these cases, regrowth phase hair lacks pigmentation or is hypopigmented. Nevertheless, recurrence rate is high [3, 35–37]. In case pruritus, redness, scales, or scarring is present, it is primal to exclude tinea capitis.

The main AA subtypes are as follows:

• Patchy AA. Presence of single of multiple patches of alopecia affecting the scalp. Disease duration and treatment response need to be closely monitored, since

**Figure 2.** *Clinical manifestation of alopecia areata.*

patients with persisting disease (beyond 1 year) can transition to AA totalis and universalis in a 30 and 15%, respectively [38] (**Figure 2c**).


**AA incognito and diffuse AA**. Both subtypes that have been recently described are not yet academically standardized [39]. They present as widespread hair loss without clear alopecic patches that can develop in a few weeks in AA incognito or over a more prolonged period of time, such as in diffuse AA. Even when trichoscopy can hint at the correct diagnosis, scalp biopsy is usually required to distinguish these conditions from telogen effluvium [28, 40].

Nails can also be affected, especially in the most severe forms of AA, such as AA universalis and AA totalis. Nail changes can present as pitting, trachyonychia, onychorrhexis, or non-specific nail dystrophy that may cause pain and cosmetic disfiguration. Findings can precede or be concurrent to the onset of AA.

Pull test, which consists on gently traction of hair at periphery of the alopecia patch, will be positive when disease is active, revealing dystrophic anagen and telogen hairs [41, 42].

The diagnosis of AA is clinical and can be made taking into consideration the aforementioned clinical features. Nevertheless, the role of trichoscopy has proven to be valuable when assessing AA, its activity state and to identify rare forms of AA [43]. Active patches of AA display yellow dots, exclamation mark hairs, and broken hairs as well as Pohl-Pinkus constrictions (**Figure 3**). Conversely, inactive patches can be identified by the presence of yellow dots and vellus hairs. Pigtail hairs and upright regrowing hairs can be spotted during remission [44–48].
