Localized Urinary Bladder Amyloidosis as Urothelial Cancer Mimicker.

Abstract

Localized amyloidosis of the bladder is rare and often mimics bladder malignancy. It is typically associated with the extracellular deposition of monoclonal light chains, either κ or λ. The cause is unknown, but it is thought to be due to chronic inflammation/cystitis. To highlight the importance of localized urinary bladder amyloidosis as a rare mimicker of urothelial malignancy and elucidate its clinical, histopathologic, and cytopathologic manifestations. Cases of urinary bladder amyloidosis diagnosed during 2000-2023 were retrieved retrospectively from pathology archives. Electronic medical records, including cystoscopy findings and pathology slides including Congo red stain, were reviewed. Here we present 6 patients with localized urinary bladder amyloidosis. Four of the 6 patients were women, with ages ranging from 46 to 69 years, and a mean age of 58 years. Five of 6 patients presented with hematuria, while in 1 patient, bladder amyloidosis was discovered incidentally. Cystoscopy findings invariably were concerning for malignancy, with raised erythema in 5 patients and fungating mass protruding into the bladder lumen in 1 patient. Bladder biopsies and urine cytology were negative for malignancy in all cases. Congo red-positive amyloid deposits involved lamina propria with sparing of the detrusor muscle. In 5 cases, the deposits were typed as derived from the λ light chain, whereas no information was available for 1 patient. Subsequent clinical workup ruled out systemic amyloidosis. These cases of urinary bladder amyloidosis highlight the importance of considering rare amyloidosis in the differential diagnosis of hematuria and cystoscopy with a lesion mimicking malignancy.