45 y.o. referred for 4+ proteinuria. Patient is asymptomatic without edema but the FLP shows total cholesterol to be pushing 300. The patient reports for one month he has seen bubbles in his urine. A 24-hour urine showed 2,500 mg of protein on an adequate specimen.
PMHx is significant for gout which has been treated with allopurinol without much improvement. Over the last couple of years he has gone from 100 mg to 300 mg, during this time his uric acid has stayed a midling 7-9 mg/dL. Two months ago he was started on probenecid, a uricosuric agent. This is appropriate as his renal function is great (S Cr of 0.9 in a male who works out).
His physical exam is benign.
No additional relevent data can be gleaned from his labs.
What’s the diagnosis?
Proteinuria due to probenecid. The patient stopped the offending agent and within ten days the U/A showed 1+ proteinuria and the PCR was 0.37.
In the exam room I told him it was a membranous nephropathy but according to this letter to NDT from 2007 the pathology is not typically membranous at all. This jives with the rapid recovery from proteinuria after the medicine is withdrawn.
Here is the mechanism of action of probenecid from UpToDate:
MECHANISM OF ACTION — Competitively inhibits the reabsorption of uric acid at the proximal convoluted tubule, thereby promoting its excretion and reducing serum uric acid levels; increases plasma levels of weak organic acids (penicillins, cephalosporins, or other beta-lactam antibiotics) by competitively inhibiting their renal tubular secretion