Mechanism of low serum sodium levels in Mediterranean spotted fever.

Prominent degrees of hyponatremia are detected in the severe forms of Mediterranean spotted fever and the intensity of this abnormality parallels the severity of the infectious process. In order to determine the incidence, degree and evolution of hyponatremia in 110 patients with Mediterranean spotted fever and to explore the feasible renal mechanism that could lead to this phenomenon, serum and urinary osmolality and levels of urea, creatinine and electrolytes were measured in samples obtained at selected points (up to the fifth week) in the course of the disease, and parameters of renal function were calculated. Mean serum sodium levels of 135.6 +/- 5.5 mEq/l were detected during the acute phase of the infection. At this point, 42 patients (38.2%) had sodium concentrations less than or equal to 135 mEq/l. After recovery, mean serum sodium values were 142.5 +/- 2.5. The analysis of the parameters of renal function indirectly rules out an inappropriate antidiuretic hormone secretion or renal failure as the cause of hyponatremia. As tubular incompetence to reabsorb sodium is also rejected in these patients, a shifting of sodium to the interstitial or intracellular space may account for the phenomenon.