Eosinophilic cystitis refractory to multiple treatments with good response to benralizumab: case report.

BACKGROUND: Eosinophilic cystitis is a rare inflammatory bladder disorder characterized by eosinophilic infiltration of the bladder wall. It frequently mimics infectious, inflammatory, or malignant conditions, and its management remains challenging due to the lack of standardized treatment. Although corticosteroids are commonly used, many cases are refractory and may require invasive procedures such as cystectomy. We report a novel case of severe, treatment-refractory eosinophilic cystitis without peripheral eosinophilia that achieved sustained remission with benralizumab, an anti-interleukin-5 receptor alpha monoclonal antibody, highlighting a promising therapeutic alternative. CASE PRESENTATION: A 44-year-old male with a history of allergic rhinoconjunctivitis presented with severe daily macroscopic haematuria requiring multiple hospitalizations, suprapubic pain, urinary urgency, and dysuria causing significant sleep disturbance. Cystoscopy showed diffuse erythematous areas, and bladder biopsy confirmed acute eosinophilic infiltration. Other causes (neoplasia, infection, parasites) were excluded. The patient was refractory to multiple courses of antibiotics, antihistamines, and corticosteroids, with only transient improvement.Off-label treatment with subcutaneous benralizumab 30 mg every four weeks (later every eight weeks) was initiated. Oral corticosteroids were discontinued after one month. After more than one year of follow-up, the patient achieved complete resolution of haematuria and bladder tenesmus, with nocturnal urgency reduced to once nightly, resulting in marked improvement in quality of life. No adverse events were observed. CONCLUSIONS: This case demonstrates the efficacy and safety of benralizumab in refractory eosinophilic cystitis, even in the absence of peripheral eosinophilia. Anti-IL-5/IL-5R monoclonal antibodies may represent a valuable steroid-sparing and surgery-sparing therapeutic option for selected patients with refractory disease. Further studies are warranted to confirm these findings and define the role of biologic therapy in this rare condition.