**8. Diagnosis and classification**

The absence of a pathognomonic test to identify HS may delay the diagnosis [21]. Three clinical diagnostic criteria are used: the presence of typical lesions, typically affected regions, and chronicity [24, 25].

The typical lesions are painful nodules, abscesses, suppurative sinus tracts, coalescing scars, and complex comedones. Pruritus, fetid smell, pain, and burning sensation are the most common symptoms. Affected regions must include at least one of the following: axillary, infra- and intermammary, inguinal, perineal, perianal, and gluteal regions. Chronicity is characterized by persisting lesions over 3 months or two recurrences within the period of 6 months. Secondary bacterial infection may also cause chronicity [21, 23–25].

Familiar HS history must be considered and a full skin examination performed to assess the severity and exclude other diagnoses [21, 26].

The skin biopsy may be useful and should be performed if there is suspicion of squamous cell carcinoma. A firm, nonfluctuant, nondraining, superficially eroded, or ulcerated mass are strong evidence of malignancy [22].

If there is a primary infectious disease or clinical evidence of secondary cellulitis, a culture may help [21, 25, 26].

High-frequency ultrasound and magnetic resonance are used to detect dermal and subcutaneous involvement, discriminating differential diagnosis, such as fistula [21, 27].

HS severity is classified by the Hurley classification, which defines three stages according to the number, chronicity, and coalescence of the lesions as shown in **Table 3** [21].

Sartorius scoring system and international hidradenitis suppurativa severity score system (IHS4), most appropriate to assess disease severity and grade of inflammation, was later proposed (**Tables 4** and **5**) [21, 24].

Three clinical subtypes of HS have been described: axillary-mammary, follicular, and gluteal. According to another classification by van der [26], there are six phenotypes of HS: (I) regular type; (II) frictional furuncle type; (III) scarring folliculitis type; (IV) conglobata type; (V) syndromic type; and (VI) ectopic type. Recently, it has been suggested to distinguish between a follicular subtype and an inflammatory phenotype, which is usually associated with a worse course of the disease [21, 26, 27].


#### **Sartorious score**

I—Anatomical region involved (axilla, groin, gluteal or other region or inframammary region left and/or right: 3 points per region).

II—Number and scores of lesions (abscesses, nodules, fistulas, scars: points per lesion of all regions involved: nodules 2, fistulas 4, scars 1, others 1).

III—The longest distance between two relevant lesions, i.e. nodules and fistulas, in each region, or size if only one lesion (<5 cm, 2 points; < 10 ,4 *cm* points; > 10 ,8 *cm* points).

IV—Are all lesions clearly separated by normal skin? In each region (yes 0 / no 6).

*Adapted from Sartorius et al. [24].*

#### **Table 4.**

*Sartorious score.*


#### **Table 5.**

*International Hidradenitis Suppurativa Severity Score System (IHS4).*
