What are the symptoms of Diabetes Insipidus (DI), including typical water intake and urine output?

Symptoms of Diabetes Insipidus

Diabetes insipidus presents with massive polyuria (excretion of abnormally large volumes of dilute urine) and severe polydipsia (excessive thirst), with the hallmark being inappropriately diluted urine (osmolality <200 mOsm/kg H₂O) combined with high-normal or elevated serum sodium—this triad is pathognomonic for the condition. 1, 2

Core Clinical Manifestations

Primary Symptoms

• Polyuria: Patients excrete copious volumes of dilute urine with osmolality typically <200 mOsm/kg H₂O, though it can be higher in milder cases 1
• Polydipsia: In older children and adults, excessive thirst and fluid-seeking behavior is the predominant symptom at diagnosis 1, 2
• Hypernatremia risk: Serum osmolality is usually >300 mOsm/kg H₂O due to hypernatremia when fluid access is restricted 1

Age-Specific Presentations

Infants and Young Children (mean diagnosis age ~4 months):

• Failure to thrive and growth failure 1, 2
• Feeding difficulties and "greedy" drinking followed by vomiting 1
• Signs of dehydration and hypernatremic dehydration 1, 2
• Gastro-oesophageal reflux exacerbated by large fluid volumes 1
• Preference for water over nutritional fluids with delayed transition to solid foods 1

Adults:

• Polydipsia is the predominant presenting symptom 1, 2
• Polyuria with volumes >2.5 L per 24 hours despite attempts to reduce intake 3

Actual Fluid Volumes: Water Intake and Urine Output

Quantitative Measurements

Infants and Children with Nephrogenic DI:

• Water intake requirement: 100-200 mL/kg/24h or more, which translates to several liters daily 4
• For a 10 kg infant, this means 1-2 liters minimum per day, often substantially more

General Urine Output:

• Patients produce copious volumes of dilute urine continuously 5, 6, 7
• Urine output closely matches fluid intake when access to water is unrestricted 1
• Drug treatment can reduce diuresis by up to 50% in the short term when thiazide diuretics plus prostaglandin inhibitors are combined with a low-salt diet 1, 4

Practical Implications

• Night-time volumes: Children experience "bed flooding" due to massive urine volumes, with some parents using "double nappies" (a larger adult diaper around the child's usual diaper) and changing diapers multiple times during the night 1
• Nocturnal enuresis: Full continence is usually reached only in the second decade of life, with night continence achieved at a median age of 8-11 years 1
• Bladder dysfunction: The constant high-volume urine flow can cause urinary tract dilatation and incomplete voiding, observed in 46% of patients in one study 1

Critical Management Considerations

Fluid Access Requirements

• Patients must have 24/7 access to water, including overnight, to prevent life-threatening dehydration and hypernatremia 4, 3
• Patients capable of self-regulation should determine their own fluid intake based on thirst sensation rather than prescribed amounts—their osmosensors are more sensitive and accurate than medical calculations 1, 3
• Infants are particularly at risk as they have no free access to fluid and cannot express thirst clearly 1

Nutritional Challenges

• 20-30% of children with nephrogenic DI require tube feeding at some point to ensure adequate nutrition and hydration, though this is rarely continued beyond 4 years of age 1, 4
• Normal-for-age milk intake (instead of pure water) is essential in infants to guarantee adequate caloric intake 1, 4

Emergency Situations

• When fasting is required for >4 hours (e.g., before anesthesia), intravenous 5% dextrose in water should be provided at usual maintenance rates, NOT normal saline 1, 4
• Close monitoring of weight, fluid balance, and biochemistry is crucial, as urine volume typically decreases considerably with IV glucose administration 1
• Every patient should have an emergency plan and medical alert identification explaining their diagnosis with specific IV fluid management instructions 4

Common Pitfalls to Avoid

• Do not restrict fluid access in attempts to "control" polyuria—this leads to dangerous hypernatremia and dehydration 1, 3
• Monitor closely when starting drug treatment: marked hyponatremia can occur if patients maintain unchanged high fluid intake after commencing medications that reduce urine output 1
• Avoid normal saline for IV hydration—use dextrose 5% in water instead to prevent osmotic load 1, 4
• Regular glucose monitoring is needed during IV dextrose administration as hyperglycemia can cause osmotic diuresis 1