Selective
hypoaldosteronism is defined as diminished production of
aldosterone, and sometimes also of
18-hydroxycorticosterone, with otherwise intact adrenal function. A decrease in the secretion of
potassium and H+-
ions and in the reabsorption of
sodium in the distal nephron may result and lead to
hyperkalemia, hyperchloremic
acidosis, and impaired renal
sodium conservation. The form of
hypoaldosteronism which occurs in the adult is characterized by the following additional features: the
aldosterone deficiency is due in the majority of cases to a decrease in enzymatically active plasma
renin ("
hyporeninemic hypoaldosteronism"), while various endogenous mechanisms as well as certain drugs (
prostaglandin inhibitors, beta-blockers) may contribute. Other disturbances of the renin-angiotensin system (e.g. during treatment with converting-
enzyme inhibitors) may rarely be responsible. Abnormalities in adrenal cortical synthesis may sometimes coexist, but proof that adrenal enzymatic defects play a primary pathogenic role in selective
hyperaldosteronism in the adult is lacking. Such patients are frequently older (greater than 50 years), and often have
diabetes mellitus and/or
nephropathy (diabetic, interstitial, or
hydronephrosis).
Hyperkalemia and
acidosis tend particularly to develop in association with mild to moderate impairment of renal function. The differential diagnosis should include other causes of impaired renal
potassium secretion (
Addison's disease, renal resistance to
mineralocorticoids,
potassium-sparing diuretics). Moreover, possible extrarenal factors contributing to
hyperkalemia (oral
potassium intake and redistribution of intracellular/extracellular space, particularly with associated
insulin deficiency) should also be considered. For treatment,
dietary potassium restriction is recommended as a general step. Replacement with the
mineralocorticoid fludrocortisone acetate usually reverses the
hyperkalemia and
acidosis, but may sometimes induce
sodium retention and
hypertension.
Loop diuretics,
potassium-exchanging preparations and/or
bicarbonate may also be useful as alternatives or additives.