Case 3: Polyuria and Polydipsia in an 11-year-old Boy

Presentation

An 11-year-old boy presents to the emergency department (ED) with a 1-month history of intermittent vomiting and fatigue. Further history revealed a 10-lb (4.5-kg) weight loss during the past few months, progressively decreasing energy and appetite, and polyuria and polydipsia for more than 2 months. Within the past month he was observed drinking approximately 2 gal (7.6 L) of water a day and urinating 10 or more times a day, including 2 to 3 times during the night. Although he did not endorse a history of headache, weakness, or paresthesia, he reported intermittent blurry vision and dizziness. During the past few months, he had been evaluated by his pediatrician multiple times for these concerns.

Six months before ED presentation his weight was 93.7 lb (42.5 kg) (74th percentile) and his height was 60 in (152.4 cm) (85th percentile). Two weeks before the ED visit his weight had declined to 86.6 lb (39.3 kg) (45th percentile) and his height was 61 in (155 cm) (82nd percentile), indicating a change in BMI from 18.3 (65th percentile) to 16.4 (34th percentile) during this period. He had undergone evaluations for diabetes mellitus and diabetes insipidus (DI), which were negative; results of an upper gastrointestinal series were negative as well. A serum osmolality ordered by his pediatrician 10 days before his ED visit was 292 mOsm/kg (292 mmol/kg) (normal range, 278–305 mOsm/kg [278–305 mmol/kg]); urine osmolality was 99 mOsm/kg (99 mmol/kg) (normal range, 50–1,200 mOsm/kg [50–1,200 mmol/kg]), and his serum sodium level was 137 mEq/L (137 mmol/L) (normal range, 135–146 mEq/L [135–146 mmol/L]).

On ED arrival his vital signs were stable. Physical evaluation showed …