ALTERED RENAL HANDLING OF ELECTROLYTES IN A CHILD WITH CENTRAL DIABETES-INSIPIDUS (CDI)

A 12-year-old female child, with a history of polyuria and polydipsia of about three years duration, was admitted to Ethio-Swedish Paediatri c Hospital, in Addis Abeba. Urine output in 24 hours averaged 5-6 litr es, with a frequency of 15 times during the day and 7-8 times during t he night. Random urine analysis showed an osmolality of 60 mOsm/kg, Na + 27.1mmol/L and K+ was 7.6 mmol/L. Basal plasma osmolality was 313mOs m/kg with Na+ being 156mmol/L and K+ 4.06 mmol/L. Water deprivation fo r nine hours failed to produce a concentrated urine, which was only 13 8mOsm/kg at the end of the test, with a corresponding plasma osmolalit y of 336 mOsm/kg. After nine hours of water deprivation, urine Na+ inc reased from 27.1 to 37.3 mmol/L while K+ increased from 7.1 to 18.7 mm ol/L. Lypressin, a vasopressin analogue, at a concentration of 0.3 IU/ kg injected intramuscularly, resulted in a marked increase in urine os molality to 586 mOsm/kg within two hours, associated with relief of sy mptoms. Urinary excretion of K+ was markedly increased during the vaso pressin test while Na+ excretion was little affected. A case of centra l diabetes insipidus of undefined etiology is presented and the possib ility of altered renal handling of electrolytes and an abnormal respon se to vasopressin in such cases is noted. The problem of management an d the currently available treatment options are summarized.