The majority of patients improved with ustekinumab. Although no biomarker was discovered, low LTA4H concentrations with mild disease severity may be predictive of the effectiveness of ustekinumab.

Hidradenitis suppurativa (HS) is a difficult disease to treat. Although the pathogenesis of this inflammatory skin disease is largely unknown, the important role of the immune system has been demonstrated in both experimental and clinical studies. Clinicians are therefore increasingly prescribing systemic treatments with immunosuppressive agents, but the more traditionally used systemic retinoids, especially isotretinoin, also remain relatively common therapies. In order to provide an overview of all currently available systemic immunosuppressive agents and retinoids for the treatment of HS, a systematic search was performed using the Medline and Embase databases. All published papers concerning systemic retinoids or immunosuppressive treatments for HS in adults were included. The primary endpoints were the percentages of significant responders, moderate responders and nonresponders. Other endpoints were the relapse rate and adverse events. In total 87 papers were included, comprising 518 patients with HS who were treated with systemic retinoids, biological agents or another immunosuppressive agents, including colchicine, ciclosporin, dapsone or methotrexate. The highest response rates were observed with infliximab, adalimumab and acitretin. Overall, the quality of evidence was low and differed between the agents, making direct comparisons difficult. However, based on the amount of evidence, infliximab and adalimumab were the most effective agents. Acitretin was also effective in HS, although the quality of the evidence was low. The therapeutic effect of isotretinoin is questionable. Randomized controlled trials are needed to confirm the effectiveness of acitretin, and to identify the most effective immunosuppressive agents in HS.

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The diagnostic delay in HS is long due to a lack of knowledge in both patients and health care professionals, indicating that there is a need for education. Deroofing and the STEEP are effective surgical procedures in severe cases of HS and lead to a relatively high patient satisfaction. The postoperative relapse risk is higher in women. Prospective studies are required for the development of clear guidelines on the appropriate choice of surgery.

Sir, Hidradenitis suppurativa (HS) is a chronic, recurring, debilitating inflammatory skin disease, which mainly affects the inverse areas of the body leading to scarring and disfigurement (1, 2). The European S1 guideline for the treatment of HS summarized all published treatments for HS (1). The quality of evidence for these treatments is generally low, as was recently demonstrated in a Cochrane Review on interventions for HS, which identified only 12 randomized controlled trials (RCTs) (3). Moreover, HS is a heterogeneous disease with distinct clinical phenotypes that may require different treatment strategies, further complicating the therapeutic decision-making process (4). The European S1 guideline proposed a "Hurley severity grade-relevant treatment algorithm" (1). More recently Gulliver et al. (5) proposed another treatment algorithm based on disease severity measured by Hurley grade or PGA. Hurley stage is a 3-stage classification of severity. Hurley stage I is characterized by abscess formation with out sinus tracts and scarring. In Hurley II, patients have single or multiple separated areas of recurrent abscesses with sinus tracts and scarring, whereas in stage III the multiple interconnected sinus tracts and abscesses cover the whole affected anatomical area. This classification in its original form was created mainly for surgical purposes and does not take into account the inflammatory component. In addition, the extension of the disease, i.e. the number of anatomical areas involved, is not assessed. Accurate stratification of the wide variety of HS clinical phenotypes is therefore not possible with the original Hurley score. Furthermore, the recently invented dynamic scoring system Hidradenitis Suppurativa Clinical Response (6) focuses mainly on the inflammatory component and is more or less comparable with a PASI 50 improvement in psoriasis and therefore is mainly suitable for the follow-up of systemic Departments of Dermatology,

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In contrast to wide excisions that generally reach into the deep subcutaneous fat, the fat is maximally spared with the STEEP procedure by performing successive tangential excisions of lesional tissue until the epithelialized bottom of the sinus tracts has been reached. From here, secondary intention healing can occur. In addition, fibrotic tissue is completely removed in the same manner as this also serves as a source of recurrence. This tissue-sparing technique results in low recurrence rates, high patient satisfaction with relatively short healing times and favourable cosmetic outcomes without contractures.

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