[The long-term administration of dexamethasone for the differentiation of the 4 types of hyperaldosteronism].

To elucidate the significance of long-term administration of dexamethasone in order to differentiate the 4 types of hyperaldosteronism, blood pressure, serum electrolytes, plasma renin activity (PRA) and diurnal rhythm of plasma aldosterone (PAC) were studied before and after long-term dexamethasone (Dex) administration in patients with aldosterone-producing adenoma (APA), idiopathic hyper aldosteronism (IHA), unilateral adrenal hyperplasia (UAH) and Dex suppressible hyperaldosteronism (DSH). The results were as follows: 1) In APA with ACTH-dependent aldosterone secretion, long-term Dex administration induced a significant depression of PAC associated with an elevation in serum potassium (s-K). In almost all patients with APA, the diurnal rhythm of PAC, parallel to that of ACTH, completely disappeared following Dex administration. 2) In most patients with IHA, PAC was mainly influenced by the renin-angiotensin system. Dex did not affected on s-K, but it induced a slight decrease in PAC in some patients with IHA. 3) In UAH having similar pathophysiological findings of the adrenal cortex as IHA, Dex decreased PAC. 4) In DSH, Dex at a dose of 6 mg/day decreased PAC to normal value in association with normalization of blood pressure and s-K. From these results, hyperaldosteronism inducing a decrease in PAC and an increase in s-K by Dex is possibly diagnosed as APA, while the patients with no change of s-K by Dex may be diagnosed as IHA. Even if PAC is suppressed with Dex and ACTH-independent, the hyperaldosteronism may be UAH. It may be possible that factors other than aldosterone are important to induce hypokalemia in patients with IHA. Furthermore, it is suggested that UAH is a precedent pathophysiological condition of aldosterone-producing adenoma in the adrenal cortex. It is concluded that the measurement of s-K and diurnal rhythm of PAC before and after Dex administration are useful for discriminating APA and IHA.