Study of sweat in pitressin-resistant diabetes insipidus

Increased sweat electrolyte concentrations, sodium 60 to 70 mEq. per liter, chloride 50 to 60 mEq. per liter, potassium 15 to 20 mEq. per liter were observed in a 41/2-month-old child with pitressin-resistant diabetes insipidus who initially did not exhibit excessive thirst. Administration of large doses of 9 alpha-fluoro-hydrocortisone did not affect these values. Hydrochlorthiazide therapy was associated with immediate clinical improvement and marked decrease in sweat sodium and chloride concentrations. Hydrochlorthiazide caused clinical improvement despite increased urine volume during therapy. All observations of elevated sweat electrolytes in pitressin-resistant diabetes insipidus have been in infants less than 10 months of age and not solely in infants without excessive thirst. Therefore sweat analysis may be an aid to diagnosis in infants when clinical recognition is difficult.