The Diuretic Response to Administered Water in Patients With Primary Myxedema

The diuretic response to administered water was studied in 8 patients with typical, untreated primary myxedema. The maximal rate of urine flow was definitely reduced below the normal range (minimum, approximately 8 ml. per minute) in 2 of the 8 patients. In each of 5 patients re-studied following treatment with desiccated thyroid, including 3 whose pre-treatment peak flow of urine was greater than 8 ml. per minute, there was an increase in maximal diuretic response. The urine during periods of maximal flow after treatment was more dilute than before treatment in 4 of these patients. The rate of total solute or sodium excretion did not bear a consistent relationship to increased urine flow. Endogenous creatinine clearance increased significantly after treatment in all 5 patients. The modest limitation in water diuresis observed in primary myxedema may be attributed to a reduction in glomerular filtration rate. That the diuretic response to water is a useful test to differentiate primary myxedema from panhypopituitarism with secondary myxedema has been confirmed.