Disorders of urinary acidification in patients with monoclonal gammapathies

BACKGROUND: In patients with monoclonal gammapathy (MG), renal impairment becomes the frequent complication. At the same time, its exact pathogenetic mechanism remains to be identified. We tried to detect urinary acidification defect that may become the first sign of the kidney parenchymal injury. The goal of our work was to estimate the incidence of the acidification impairment, the contribution of proximal and distal types of renal tubular acidosis and the dependency of the defect on the type of light chain paraprotein. METHODS AND RESULTS: In the group of 21 patients aged 38 to 82 years (14 females and 7 males) with monoclonal gammapathy accompanied with creatinemia lower than 180 micromol/l, the short acidification test was performed (calcium chloride was administrated and the urinary acidity was monitored). Renal tubular acidosis was diagnosed in those patients whose urinary acidity after the CaCl2 administration did not reach pH 5.25 or less. The control group consisted of 19 volunteers (6 males and 13 females) with normal renal functions. Results of the tests in MG patients and in control persons were compared using the unpaired Student's t-test. In 11 patients (52.4%) the urinary acidification defect of the incomplete type was detected. Eight of these patients (38.1%) had the distal and three (14.3%) had the proximal type of impairment. Eight patients with the acidification defect had the paraproteinuria kappa and four of them had that of lambda type. In persons without the acidification impairment kappa chains were found in 5 persons, lambda chains in 4 of them. CONCLUSIONS: In our group of MG patients acidification defect occurred in more than half of them. Contrary to the assumed higher nephrotoxicity of the lambda chains, the disturbance was more frequently found in patients with paraproteinemia of the kappa type.