Etiology

Most investigators agree that HS is caused by follicular occlusion and secondary infection of apocrine sweat glands. However, genetic, immunologic, and hormonal factors may influence the development of the disease. Pathologic analysis of resected specimens suggests that compromised support of the follicular unit results from the specific abnormalities seen immunohistochemically. Elevated levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-10, and matrix metalloproteinase-2 have been found in tissues of patients with HS. Upon recognition that TNF inhibitors affect the disease, studies have been performed in an attempt to identify the relevant pathways. Although involvement is limited to areas of the body with apocrine glands, these glands are present with the same density and size in patients with HS as in control subjects. Deodorants and shaving do not seem to affect disease development. Obesity seems to be associated with HS, but it is unclear whether this association is due to related hormonal changes or associated dermal trauma.

Patients with HS often have a family history of the disease (in one study, 18 of 70 patients were reported to have a family history), supporting a genetic predisposition. However, no consistent genetic cause has been identified. Smoking is significantly more common in patients with HS than in matched control subjects. HS occurs in patients with other chronic inflammatory conditions, most notably Crohn disease, although causal relationships have not been established. Negative bacterial cultures from HS lesions are common, and the exact role of infection in persons with HS is controversial. Infection probably plays a secondary role and likely worsens the progressive scarring seen in later stages of the disease. Cultures of deeper tissues may not have the same results as those of more superficial lesions.

Clinical Presentation and Evaluation

HS initially appears as painful, round, subcutaneous nodules that may resolve or progress over days or weeks to abscesses. These abscesses do not typically point to the surface as with staphylococcal infections but rather become progressively inflamed and swollen, causing deeper dermal involvement. These abscesses often spontaneously rupture and may drain seropurulent malodorous debris. Symptoms may spontaneously improve in one area with no significant treatment but often recur in another area and frequently become progressive. Disease may affect only one site or multiple areas simultaneously. Areas of suppuration may coalesce and fistulize to adjacent tissues, resulting in subcutaneous tracts or sinuses with significant associated induration. In later stages of the disease, chronic inflammation results in multiple draining sinuses from underlying suppuration and leads to significant scarring. Skin contractures in the axilla or groin may eventually develop. Over the long term, patients with HS have a 2% to 4% risk of developing squamous cell carcinoma in the scars.

Although it is rarely life threatening, HS is a debilitating, painful, recurrent condition that causes significant alteration in quality of life. Many patients experience embarrassment and social isolation and struggle with job retention because of recurrent exacerbations of the disease.

Because perianal sepsis frequently has a cryptoglandular source and other perianal dermatological diseases exist, the diagnosis of perianal hidradenitis may not be obvious. The differential diagnosis includes pilonidal disease, anal fistula, or perianal Crohn disease. Careful examination with appropriate lighting and anoscopy is required to establish the diagnosis and rule out other causes. At times, examination after induction of anesthesia is necessary to trace fistulous connections and confirm that the anal canal is not involved. A diagnosis of HS is suggested by the multiple superficial cutaneous scars. None of the sinuses or fistulas extends to the dentate line, in contrast to cryptoglandular sepsis, which originates in the anal crypts.