Case presentation A 68-year-old Hispanic woman presented with a third episode of cystitis. She complained of multiple episodes of dysuria, frequency and suprapubic discomfort for the past six months. She denied fevers, chills, hematuria and flank pain. There was no history of nephrolithiasis and she had no other complaints. Her symptoms responded to oral levofloxacin, administered for 14 days after each episode of infection; however, they recurred a few weeks thereafter. Her medical history was significant for diabetes mellitus that was well controlled on oral hypoglycemic agents. She did not smoke, had immigrated to the United States 45 years previously and had a negative purified protein derivative test on intake. She was married with three healthy children, was a homemaker and had no contact with animals. On examination, the patient was afebrile, with a temperature of 37.6°C. Her blood pressure was 126/78 mmHg, heart rate was 82 beats/min and her oxygen saturation was 97% on room air. She was awake, alert and not in acute distress. Her skin was intact with no rashes or lymphadenopathy. She had clear lung fields, regular heart sounds without murmurs and soft nontender abdomen with no organomegaly. She had no renal angle tenderness and no lymphadenopathy. Her neurological examination was nonfocal. Blood tests revealed a hemoglobin level of 97 g/L and white blood cell count of 8.4×109 cells/L. She had chronic kidney disease with a creatinine level of 133 μmol/L. Her liver function tests were normal. Urinalysis revealed a white blood cell count of >100 cells per highpower field, with hematuria and proteinuria. Routine urine culture was negative. A computed tomography scan of the abdomen and pelvis showed normal kidney size with no stones, and a thickened urinary bladder wall with no ascites or lymphadenopathy. The patient underwent cystoscopy and biopsy (Figures 1 and 2). What is your diagnosis?