Answer: Amyloidosis

Histology: The urothelium is somewhat corrugated, but it lacks true papillary formations and there is no evidence of dysplasia. There is chronic inflammation and scattered multinucleated stromal giant cells in the lamina propria. The vessels in the lamina propria are cuffed by an eosinophilic amorphous material.

Discussion: Amyloidosis is a heterogeneous group of disorders associated with extracellular deposition of protein in a characteristically abnormal fibrillar form. Amyloidosis may be primary (AL), secondary (AA), or hereditary; and the deposits may be localized or systemic. The amyloid fibrils in primary systemic amyloidosis are derived from monoclonal immunoglobulin light chains (AL type). Systemic amyloidosis is progressive and usually fatal. Most localized amyloidosis occurs in the respiratory tract, lower genitourinary tract, and skin. Localized amyloidosis is usually of the AL type but rarely also can be of the AA type.

Localized amyloidosis of the urinary bladder is rare but is of interest because it can be mistaken for a bladder neoplasm. Primary localized amyloidosis of the bladder presents cystoscopically as a tumorlike lesion and less frequently with diffuse bladder involvement (most investigators describe the cystoscopic appearance as similar to that of an infiltrating neoplasm) and clinically with painless, gross hematuria. Histologically, it shows mainly stromal and muscle deposits of amyloid. These deposits are easily appreciated as amorphous eosinophilic aggregates that have an affinity for Congo red dye.

The cause of primary localized amyloidosis of the AL type is unknown. Chronic and recurrent mucosal and submucosal inflammation leading to chronic cystitis is postulated to cause an influx of lymphoplasma cellular elements, one of which becomes monoclonal. The monoclonal infiltrate proliferates and secretes an aberrant type of light polypeptide chain, which is amyloidogenic. Because of lysosomal proteolysis by phagocytic cells or other physiochemical means, these light chains form amyloid fibrils and are deposited in the bladder tissue.

In the absence of nephrotic syndrome, congestive heart failure, peripheral neuropathy, carpal tunnel syndrome, hepatomegaly, autonomic neuropathy, or other features suggestive of systemic amyloidosis (AL) and normal results on serum and urine immunoelectrophoresis or immunofixation, no further diagnostic procedure is necessary. Moreover, sequential evaluations for the possible development of systemic amyloidosis, particularly in otherwise asymptomatic patients, are redundant in that localized amyloidosis of the bladder generally does not progress to systemic disease.