Multiple Epidermal Cysts Following Resolution of Hidradenitis Suppurative on the Legs in a Patient with Crohn’s Disease

Dear Editor, A 43-year-old male with a 15-year history of Crohn’s disease (CD) underwent partial resection of the ileo-caecum, ileum, and ascending colon for ileus and intestinal perforation. Several years after CD onset, he developed refractory painful, inflammatory, infectious, nodular lesions on the lower extremities. Physical examination revealed inflammatory follicular occlusion, draining sinus, fistulae, and nodules on the bilateral lower extremities [Figure 1a], as well as mild lesions on the buttocks. He was a smoker, but neither symptoms of acne, arthritis, and uveitis nor family histories of similar conditions were observed. Histopathological examination showed dense inflammatory infiltrates composed of mononuclear cells and neutrophils around the follicles and sweat glands in the dermis [Figure 1b and c]. Laboratory examination showed increased white blood cell counts (23,800/mm3 with 79% neutrophils), C-reactive protein (2.15 mg/dl), and erythrocyte sedimentation rate (59 mm/h). Bacterial cultures yielded methicillin-sensitive Staphylococcus aureus. The patient was treated with drainage, oral antibiotics (minocycline 200 mg/day), and intravenous antibiotics (cephalosporin), but no improvement was observed; however, infliximab (10 mg/kg) resulted in sufficient effects on the exacerbation of his CD and cutaneous lesions after three infusions. During the course, keratotic plaques appeared on the old surgical scars on the chest and abdomen [Figure 1d], and on the lower extremities. Biopsy specimen revealed regular elongation of the epidermis with neutrophilic microabscess below the corneal layer [Figure 1e], compatible with psoriasis. The lesions triggered by a paradoxical reaction were improved by topical corticosteroid ointment. Infliximab was switched to ustekinumab for his active CD, but thereafter, multiple cystic nodules appeared on the lower extremities [Figure 1f]. Two of these nodules were surgically removed, both of which were epidermal cysts [Figure 1g].Figure 1: (a) Inflammatory nodules, fistulae, ulcers, and subcutaneous abscesses on the posterior aspect of the thighs. (b and c) Histopathological features showing prominent infiltration of mononuclear cells and neutrophils (H-E stain, b; original magnification × 40, c; ×400). (d) Scaly erythematous plaques on the operation scars on the chest and abdomen. (e) Histopathology showing regularly thickened epidermis and neutrophil infiltration in the epidermis. (f) A cystic nodule (arrow) and scars on the lower extremity. (g) Epidermal cysts (×100)Our patient had severe hidradenitis suppurativa (HS) (Hurley stage III) involving the bilateral lower extremities and buttocks, in association with active CD. The buttocks and flexural areas are most frequently involved in HS, whereas the lower extremities are rarely involved sites.[1] For the proper terminology of HS, “dissecting terminal hair folliculitis” has been proposed, because the terminal hair follicles are exclusively attacked.[2] An increased ratio of Th17/Treg, which is affected by smoking and obesity, may disturb hair follicle stem cell homeostasis, leading to infundibular dissection of terminal hair follicles and perifollicular inflammation.[3] Biologics targeting tumor necrosis factor (TNF) and IL-17 normalize the Th17/Treg ratio.[3] In the present case, infliximab was effective, but paradoxical reaction occurred, and he developed psoriasis corresponding to the old surgical scar, which was considered to be the Koebner phenomenon. After discontinuance of infliximab, his CD was treated with ustekinumab, and as his CD gradually improved, so too did his HS lesions. After the resolution of inflammation, multiple epidermal cysts without inflammation developed on the lower legs. Recent insights into the pathogenesis of HS have indicated impaired Notch signaling. Notch-deficient mice exhibit defective terminal differentiation of hair follicles, resulting in the development of epidermal cysts.[4] To date, only a few cases of multiple epidermal cysts have been reported.[5] Further studies are required to investigate the association of the occurrence of epidermal cysts and genetic mutations. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.