Reversible acute renal failure complicating rheumatoid arthritis

Although morphological and functional kidney lesions are well known to occur in rheumatoid arthritis (RA), there appear to be no previous reports on reversible acute renal failure. That interstitial nephritis plays a part in acute renal failure is clinically documented but the pathophysiology is obscure. The role of raised interstitial pressure has often been discussed but convincing evidence is still lacking. Two patients with classical RA complicated by reversible oliguria and impaired kidney function are presented. Renal biopsies revealed no glomerular, tubular or amyloid lesions. The only light microscopic finding was greatly increased interstitial edema, which stained metachromatically with toluidine blue and was hyaluronidase-sensitive. It is supposed that the abnormal concentration of interstitial hyaluronic acid and its high water-binding capacity leads to an increase of interstitial pressure, which is followed by renal insufficiency. The mucinous edema of the kidneys is assumed to be an acute reaction of the pathological connective tissue in general.