Follicular mucinosis (FM) is a disease histopathologically characterized by mucin deposition in the hair follicles; the main symptoms are papular erythema, papular pilaris, and hair loss in hairy areas (1). FM is classified as either idiopathic or secondary based on underlying diseases or complications. In recurrent or refractory cases, the disease can transform into mycosis fungoides. Treatment includes local or systemic corticosteroids, dapsone, indomethacin, interferon, hydroxychloroquine, and minocycline; however, some patients do not respond to these treatments (2). We report a case of a patient with idiopathic FM on the right cheek that was resistant to various treatments but responded well to cyclosporine. A 51-year-old Japanese woman presented with an erythematous plaque on her right cheek 2 months before the first visit to our clinic. Initial physical examination revealed cutaneous involvement only, and an infiltrative erythematous plaque with diffuse induration on the right cheek (Figure 1, a). Laboratory investigations revealed that complete blood count, antinuclear and anti-DNA antibody concentrations, and serum complement level were all within the normal range. A skin biopsy was performed, and hematoxylin and eosin staining revealed inflammatory cell infiltration in the shallow and middle layers of the dermis, mainly in the follicular and periadventitial areas, and mucus accumulation in those areas. There was no vacuolar degeneration of the epidermis. The infiltrating lymphocytes were not atypical (Figure 1, b). Alcian blue staining of the mucus revealed mucin deposition, and follicular mucin was also present (Figure 1, c). Immunohistochemical analysis revealed that the infiltrate expressed CD3, CD4, and CD8. The expression of CD8 was higher than that of CD4. We found no genetic reconstitution in the T-cell receptor β and γ chains, based on polymerase chain reaction. Idiopathic FM was diagnosed on the basis of these clinical and histopathological findings. Oral roxithromycin, topical hydrocortisone butyrate ointment, and oral indomethacin did not ameliorate the plaque. The addition of oral minocycline and dapsone also had no therapeutic effect. Treatment with 0.4 mg/kg of prednisolone per day led to improvement of the plaque; the dosage was tapered to 0.2 mg/kg per day over the course of a year; however, skin induration subsequently appeared on both cheeks, which was considered a relapse (Figure 1, d). Cyclosporine at a dose of 2.5 mg/kg per day was added to the regimen, and the symptoms did not recur even when the prednisolone dosage was reduced. Idiopathic FM may regress spontaneously, but this clinical course showed that cyclosporine was effective. Prednisolone treatment was discontinued after 3 years. Following the discontinuation of prednisolone therapy, no relapse was observed under treatment with cyclosporine alone; therefore, the plaque was considered to be controlled by cyclosporine. At present, the dosage of cyclosporine has been tapered to 1.5 mg/kg per day, and no relapse has occurred. The pathogenesis of FM is largely unknown. Lancer . reported the presence of numerous T-cells, macrophages, and Langerhans cells in the follicular epithelium of patients with idiopathic FM and speculated that cellular immunity is involved in the pathogenesis of FM (3). Our patient's case represents the first report of oral cyclosporine-related response to FM. It has been also reported that topical pimecrolimus was effective (4) and that most lymphocytes infiltrating the perifollicular area in patients with FM were CD4-positive T-cells (3), which suggests that cyclosporine was efficacious because it suppressed T-cell production. In a previous report of cyclosporine administered to a patient with atopic dermatitis and secondary FM, the course of FM was not described, but spiny follicular keratoses developed during cyclosporine administration, and all skin lesions cleared after cyclosporine was discontinued (5).5 Cyclosporine may be an effective option for the treatment of refractory FM, but it might cause adverse dermatological effects.