CHARACTERISTICS OF ALDOSTERONE-PRODUCING ADENOMA RESPONSIVE TO UPRIGHT POSTURE

A small subgroup of primary aldosteronism due to aldosteronoma, named aldosterone-producing renin-responsive adenoma (AP-RA), has been repor ted to masquerade as idiopathic hyperaldosteronism (IHA) because of th e responsiveness of the plasma aldosterone concentration (PAC) to upri ght posture (UP). We found two patients with AP-RA in 19 patients with aldosteronoma who were examined by UP stimulation and were treated su rgically. In 17 patients with typical aldosterone-producing adenoma (A PA), PAC decreased or increased only slightly (less than 200% of the b asal level); in contrast, it increased to over 300% of the basal level in two patients with AP-RA. The two groups were comparatively studied as to their hormonal levels, adrenal computed tomography (CT) scan an d histological findings in order to clarify the characteristics of AP- RA. Basal PAC was within the normal range (11.1 and 13.0 ng/dl) in AP- RA but in APA it ranged from 14.8 to 58.1 ng/dl with a mean of 32.3 +/ - 2.7 ng/dl. The diameters of the adenoma in AP-RA were apparently sma ller (6 and 9 mm) than those in APA ranged from 10 to 25 mm with a mea n of 15.5 +/- 1.1 mm. After a contrast medium was injected at CT scan, the density of the normal adrenal gland adjacent to the adenoma incre ased but that of the adenoma did not in APA, making a clear distinctio n between the adenoma and the gland. On the other hand, the density of the adenoma and gland increased to almost the same degree in AP-RA. T hus, in AP-RA it was difficult to detect adrenal tumor by CT scan beca use of its size and because of the response to the contrast medium. Ad enomas in both groups were mainly composed of clear cells, and no hist ological difference was found between the two groups. In summary, AP-R A was rarely present in primary aldosteronism and should be carefully diagnosed as primary aldosteronism because of normal PAC. Its PAC incr eased over to 300% of the basal level. It was showed that AP-RA are di fficult to distinguish from IHA not only because of the similar respon siveness of PAC to UP but also because of difficulties in detecting ad renal tumor by adrenal CT scanning.