What are the symptoms of diabetes insipidus?

Symptoms of Diabetes Insipidus

Diabetes insipidus presents with the pathognomonic triad of polyuria (>3 liters per 24 hours in adults), polydipsia (excessive thirst), and inappropriately dilute urine (osmolality <200 mOsm/kg H₂O), often accompanied by high-normal or elevated serum sodium when water access is restricted. 1, 2

Primary Clinical Manifestations

Core Symptoms in Adults

• Polyuria: Urine output exceeding 3 liters per 24 hours in adults, or more than 50 mL per kg body weight per 24 hours, representing the hallmark feature 2, 3
• Polydipsia: Excessive thirst driving fluid intake often exceeding 3 liters daily, as patients attempt to compensate for urinary water losses 2, 4
• Nocturia: Frequent nighttime urination that severely disrupts sleep, with some patients experiencing "bed flooding" particularly in children 5
• Dehydration symptoms: When fluid intake cannot match urinary losses, patients develop signs of dehydration including dry mucous membranes and decreased skin turgor 3

Pediatric Presentation

• Failure to thrive: Infants and young children show poor weight gain and growth retardation due to inadequate caloric intake relative to fluid requirements 5, 1
• Hypernatremic dehydration: Children present with elevated serum sodium (>145 mEq/L), particularly dangerous in infants who cannot communicate thirst 5
• Irritability and feeding difficulties: Infants may exhibit "greedy" drinking followed by vomiting, thought to reflect gastroesophageal reflux exacerbated by large fluid volumes 5
• Nocturnal enuresis: Older children experience bedwetting and incomplete bladder voiding from chronic polyuria 5

Biochemical Findings

Laboratory Abnormalities

• Dilute urine: Urine osmolality consistently <200 mOsm/kg H₂O despite dehydration, with urine specific gravity typically <1.005 5, 4
• Elevated or high-normal serum sodium: Serum sodium >145 mEq/L when water access is restricted, though may remain normal with adequate fluid intake 1, 3
• Elevated serum osmolality: Serum osmolality rises above normal range (>295 mOsm/kg) in the setting of inadequate fluid replacement 5

Severe or Uncompensated Symptoms

Life-Threatening Manifestations

• Severe hypernatremic dehydration: When patients cannot access water freely, serum sodium can rise dangerously high, leading to neurologic complications 5, 3
• Neurologic symptoms: Confusion, lethargy, and altered mental status develop with severe hypernatremia 4
• Encephalopathy: Severe cases progress to encephalopathy and potentially death if untreated 4
• Seizures: Can occur with rapid changes in serum sodium or severe hypernatremia 3

Important Clinical Context

Distinguishing Features from Diabetes Mellitus

• Absence of hyperglycemia: Unlike diabetes mellitus, blood glucose levels remain normal in diabetes insipidus 5
• No glucosuria: Urine does not contain glucose, distinguishing it from the osmotic diuresis of diabetes mellitus 5
• Different mechanism: Polyuria results from inability to concentrate urine due to ADH deficiency or resistance, not from glucose-induced osmotic diuresis 5

Compensatory Mechanisms

• Intact thirst mechanism: Most patients maintain normal serum sodium at steady state when they have free access to water, as their osmosensors trigger appropriate thirst response 5
• Excessive fluid-seeking behavior: Patients demonstrate compulsive water-seeking behavior and may carry water bottles constantly 3
• Preference for cold water: Many patients specifically prefer ice-cold water 3

Critical Pitfalls to Recognize

High-Risk Populations

• Infants and toddlers: Cannot clearly express thirst, making them vulnerable to severe dehydration and requiring caregivers to offer water frequently 5
• Cognitively impaired patients: Cannot self-regulate fluid intake and require close monitoring of weight, fluid balance, and serum sodium 5
• Hospitalized patients: May have restricted water access or be NPO, placing them at extreme risk for hypernatremic crisis 5

Urological Complications

• Chronic bladder dysfunction: Approximately 46% of patients develop urological complications from chronic polyuria, including incomplete bladder voiding and urinary tract dilatation 5
• Hydronephrosis risk: Long-term polyuria can lead to urinary tract dilatation requiring ultrasound monitoring every 2 years 5, 1