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Sonographic features and successful treatment of stump hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory disorder of the follicular pilosebaceous units with an estimated prevalence of 1–4 %. It is characterized by the appearance of relapsing and painful nodules that result in abscesses, draining sinus tracts and scarring, and has a profound impact on quality of life [1–5]. The exact pathogenesis of HS remains unknown. An anomalous innate immune response, genetic predisposition, obesity, skin flora, tobacco and mechanical stress are regarded as risk factors for HS [4]. It was initially believed that HS was caused by inflammation of apocrine glands, since it involves the axillary, inframammary, inguinal and anogenital regions, which are rich in these glands [2]. However, histological examination has shown that apocrinitis is not present in the majority of HS lesions and is thought to be a secondary event if present [3]. Typical sites of HS are characterized by increased mechanical friction and occlusion, not by the existence of inflamed apocrine glands. Hyperkeratinization and secondary occlusion of the follicular infundibulum due to Th17-driven inflammation are currently thought to be the main pathogenic factors in HS, and may occur in response to external factors [4]. Mechanical stress promotes keratinocyte proliferation and keratin accumulation; this can cause enlargement and debilitation of the follicular unit which finally ruptures [3], amplifying the inflammatory response. Friction and trauma also contribute to infundibular inflammation and rupture, playing an important role in HS pathogenesis [4, 6]. A warm and humid environment favors occlusion and consequently bacterial growth, which may be another factor in HS development. This might explain why HS lesions appear in the fat folds of obese patients, where maceration, pressure and shear forces add to the low-grade systemic inflammation associated with overweight [6, 7]. Recently, various case reports have been published that support the association of HS with mechanical factors: two cases of HS-like lesions developing in a nevus comedonicus subjected to mechanical stress [8, 9]; HS-like lesions due to prosthesis related friction [3]; ectopic HS on the dorsal foot induced by a tight-fitting shoe [5]; and HS-like lesions triggered by the pressure of a waistband on the upper abdomen [6, 10]. It is important to note that there is a risk of squamous cell carcinoma developing from long-standing inflammatory processes such as hidradenitis suppurativa [11, 12]. We report the case of a 32-year-old woman with a lower leg amputation due to a traffic accident four years ago, who developed long-lasting HS lesions in the axillary region and a six-month history of HS-like lesions on her leg stump after wearing a leg prosthesis. She could no longer stand with the prosthesis because of the resulting pain. Physical examination revealed inflamed nodules and draining abscesses on the stump and thigh areas (Figure 1a). The ultrasound examination showed a fistulous tract with an increased Doppler signal and edema of underlying subcutaneous tissue, consistent with Hurley stage III HS-like lesions of the stump (Figure 1b). She was treated successfully with 100 mg of doxycycline once a day for one month and topical clindamycin three times a day. There was a noticeable clinical improvement after treatment (Figure 2a). Furthermore, ultrasound showed resolution of Clinical Letter