**3.2 Disease severity**

Clinical classification of AA in subtypes provides the clinician with some insight of the severity of AA. Nevertheless, this classification system is insufficient for

#### **Figure 3.**

*Trichoscopic image of active AA. Red arrows: Pohl-Pinku constriction; yellow arrows: S black dots; white arrow: Exclamation mark hair. Image courtesy of Dr. Díaz-Calvillo.*

describing the extent of the alopecia and does not allow for assessing response to treatment. The Severity Alopecia Tool (SALT) is a visual scoring system in which the scalp surface area is divided in four views and each view (back, sides, and top view) in quadrants. The clinician assesses and adds the areas affected by alopecia, and a final score is rendered. A scoring higher than 50% is considered severe (**Figure 4**) (Olsen). Other validated scoring systems with similar methodology have been conceived for accounting for eyelashes and eyebrows such as the Brigham Eyebrow Tool for Alopecia (BETA) and the Brigham Eyelash Tool for Alopecia (BELA), respectively [49, 50].

#### **3.3 Prognosis**

Early onset, family history of AA, severe forms such as AA totalis or universalis, ophiasis, nail disease, and atopic dermatitis are factors associated with a poor prognosis [4, 40, 51–53].

#### **3.4 Histopathology**

Scalp biopsies are occasionally required in cases in which diagnosis is uncertain as it remains the gold standard. Usually, a punch biopsy at the activity border of the lesion is taken. Histopathological findings depend on the duration of the AA episode. Overall, the main feature is the presence of peribulbar lymphocytic infiltrate [28, 40]. During episodes of active hair shedding, peribulbar lymphocytic infiltrates mainly composed of lymphocytes, Langerhans cells and to a lesser extent, plasma and mast cells as well as eosinophils. This arrangement receives the name of swarm of bees. In chronic phases, inflammatory infiltrates are still present, although less evident and there is an abundance of follicles in telogen and catagen stages [28, 40]. Syphilitic alopecia does not only resemble AA clinically but also histologically. A lack

#### **Figure 4.**

*The severity alopecia tool (SALT) visual aid allows the evaluator to estimate the percentage of alopecia surface via adding the values of the affected quadrants.*

of miniaturized follicles and eosinophils and the presence of spirochetes may aid the diagnosis of syphilitic alopecia [54–56].

#### **3.5 High-frequency ultrasonography (HFUS)**

Recently, HFUS has gained some attention on the diagnosis and follow-up of hair disorders. HFUS allows to visualize deep structures in the scalp skin such as subcutaneous tissue below hair follicles. Hair follicles present with lower echogenicity than the surrounding tissue in HFUS. A group of Polish researchers characterized the findings found in different stages of AA. Active stage of AA showed presence of distinct, drop-shaped follicular structures, while during inactive stages follicular structures are reduced and undefined [57, 58].
