The
salt intake of the Japanese is among the highest in the world, leading to a high prevalence of
salt-sensitive
hypertension. To prevent this,
salt restriction, suppression of the
rennin-
angiotensin-
aldosterone system, and natriuresis are important. Therefore, the use of a combination of an
angiotensin II receptor blocker and
thiazide diuretics is used for
antihypertensive treatment. Some randomized controlled studies suggested that
thiazide diuretics are useful not only to lower blood pressure, but also to prevent cardiovascular events and improve prognosis in the elderly, who are prone to being
salt-sensitive. We encountered 2 elderly patients referred to our emergency room because of severe
hyponatremia and consciousness disturbance, who had been treated with
thiazide diuretics for 1 and 2 months, respectively. In both, hypernatriuria despite
hyponatremia, slight
dehydration, and refractory
antidiuretic hormone (ADH) excess were observed, but activation of the
rennin-
angiotensin-
aldosterone system was absent. Thyroid and adrenal functions were unremarkable. Theses phenomena have much in common with the condition called mineralcorticoid-responsive
hyponatremia of the elderly (MRHE). Several weeks after discontinuation of
diuretics, serum
sodium values returned to normal levels, but transtubular
potassium concentration gradient (TTKG) values were depleted despite slight
hyperkalemia, and relative ADH excess was sustained, which suggested
mineralocorticoid dysfunction and distal renal tubulointerstitial injury. Distal tubulointerstitial dysfunction is one of the most important causes of MRHE. On the basis of these 2 cases, we speculated whether distal tubulointerstitial injury may accelerate
hyponatremia in the elderly. We need to check not only serum
potassium, but also
sodium levels, especially in elderly persons with suspected tubulointerstitial injury.