Central diabetes insipidus

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Arginine vasopressin is synthesised in hypothalamic nuclei and released from the posterior pituitary when osmolality rises or effective circulating volume falls. It concentrates urine through renal V2 receptors. Central diabetes insipidus reflects deficient synthesis or release after pituitary or hypothalamic surgery, tumour, trauma, inflammation, infiltrative disease, infection, genetic disease or an idiopathic process. The characteristic phenotype is large-volume pale urine, intense thirst and nocturia. Frequency without high volume suggests a bladder disorder, while glucose, urea, sodium or diuretics can drive an osmotic diuresis. Measure 24-hour volume or a reliable inpatient output, then establish whether urine is inappropriately dilute relative to plasma sodium and osmolality. Review the anterior pituitary because structural causes frequently affect several axes, and protect cortisol physiology before thyroid replacement if multi-axis failure is suspected.

Management balances two opposing hazards. Without adequate AVP action, free water is lost; with desmopressin active, the kidney cannot excrete a large water load normally. A person who can drink to thirst usually self-corrects water loss, but fasting, vomiting, reduced consciousness, disability, nil-by-mouth orders or adipsia removes that defence. Society for Endocrinology guidance prioritises fluid resuscitation in decompensated disease and frequent sodium monitoring, with desmopressin response assessed carefully to prevent rapid overcorrection. Stable therapy uses the least desmopressin that controls disruptive polyuria while permitting planned aquaresis when advised. Oral, sublingual, nasal and parenteral formulations have very different bioavailability and are not directly interchangeable. Give a written sick-day plan, emergency identification, travelling advice and a route for urgent endocrine support. Use the person's verified prescribed regimen and the local inpatient protocol at the point of care.

Key points

Confirm true polyuria by measured urine volume before assuming thirst or urinary frequency represents central diabetes insipidus.
Exclude osmotic diuresis, excess drinking, kidney disease, hypercalcaemia, hypokalaemia and medicines before testing the vasopressin axis.
In decompensated AVP deficiency, restore fluid first; if excessive dilute urine persists, Society for Endocrinology guidance advises desmopressin 1–2 micrograms IV or IM, with close clinical, urine-output and serum-sodium monitoring.
A person with intact thirst and unrestricted water may maintain normal sodium despite severe AVP deficiency, so normal sodium does not exclude the diagnosis.
Water-deprivation, copeptin-based and desmopressin-response testing belong in a specialist supervised protocol because dehydration and sodium shifts can harm.
Desmopressin is life-sustaining for complete central disease, but missed doses cause water loss and excess doses or drinking without thirst cause water retention.
After pituitary surgery, distinguish transient AVP deficiency from the possible triphasic response and monitor sodium rather than prescribing an automatic fixed course.
Every hospital admission should identify desmopressin on medicines reconciliation and assess whether the person can drink, self-administer and communicate thirst.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Pituitary or hypothalamic intervention

Sellar surgery, cranial trauma or radiotherapy can damage vasopressin synthesis, transport or release, sometimes within a wider pattern of pituitary failure.

Structural or inflammatory disease

Tumours, inflammation, infiltration or infection affecting the hypothalamic-pituitary region can interrupt vasopressin pathways and may also alter thirst or anterior pituitary axes.

Idiopathic or genetic disease

Some patients have no acquired structural explanation or have an inherited defect, so specialist assessment is needed when common postoperative and tumour contexts are absent.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Vasopressin release falls
Insufficient arginine vasopressin reaches renal V2 receptors, despite rising plasma tonicity or falling effective circulating volume that should normally stimulate release.
2
Urine remains dilute
Collecting ducts cannot conserve free water appropriately, producing sustained high-volume pale urine, nocturia and a compensatory rise in thirst.
3
Water balance becomes access-dependent
A person with intact thirst can often maintain sodium, but fasting, vomiting, reduced consciousness, immobility or adipsia allows rapid dehydration and hypernatraemia.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Hypotonic polyuria

Sustained high-volume dilute urine with polydipsia and nocturia is the core syndrome; document volume because urinary frequency alone is non-specific.

Hypernatraemic decompensation

Thirst, dry mucosa, weight loss, tachycardia, hypotension, confusion or reduced consciousness with rising sodium suggests water loss exceeding access or ability to drink.

Desmopressin water intoxication

Headache, nausea, weight gain, confusion or seizure after desmopressin with high fluid intake may represent dilutional hyponatraemia and requires urgent sodium assessment.

Structural hypothalamic-pituitary disease

Headache, visual symptoms, anterior pituitary deficits, stalk thickening, cancer, trauma or recent sellar surgery increases the likelihood of central rather than renal disease.

Impaired thirst

Absent thirst despite hypernatraemia or a hypothalamic lesion identifies exceptional risk because physiological drinking no longer protects against uncontrolled water loss.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Measured 24-hour urine volumeFirst step
Why
Confirm genuine polyuria and quantify severity before endocrine provocation.
Interpretation and limitations
A high volume supports a water or solute diuresis; normal volume redirects assessment towards urinary frequency, nocturia or perceived thirst.
02
Paired plasma and urine osmolality with sodium
Why
Relate circulating tonicity to renal concentrating behaviour.
Interpretation and limitations
Dilute urine despite high or high-normal plasma osmolality supports impaired AVP action; low plasma osmolality suggests primary excess intake, while intermediate patterns need specialist testing.
03
Glucose, calcium, potassium and renal profile
Why
Identify common solute diuresis, electrolyte and kidney explanations for polyuria.
Interpretation and limitations
Hyperglycaemia, hypercalcaemia, hypokalaemia or impaired renal concentration should be corrected or incorporated before attributing symptoms to central AVP deficiency.
04
Supervised dynamic water-balance test
Why
Distinguish AVP deficiency, AVP resistance and primary polydipsia when basal assessment remains uncertain.
Interpretation and limitations
Interpret weight, sodium, plasma and urine osmolality and desmopressin or copeptin response under the centre's validated protocol; inadequate stimulus or unsafe termination makes the result non-diagnostic.
05
Pituitary MRI
Why
Identify a structural hypothalamic, stalk or pituitary cause after biochemical confirmation or when mass-effect features exist.
Interpretation and limitations
Loss of the posterior bright spot is not specific. Stalk lesion, mass or infiltrative change requires full pituitary, oncological and sometimes inflammatory investigation.
06
Anterior pituitary hormone assessment
Why
Detect associated ACTH, thyroid, gonadal, growth-hormone or prolactin disturbance.
Interpretation and limitations
Multiple deficits support hypothalamic-pituitary disease; suspected cortisol deficiency needs urgent protection and affects the water-balance phenotype after glucocorticoid replacement.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Primary polydipsia

Excess fluid intake lowers plasma tonicity and appropriately suppresses vasopressin; supervised specialist testing separates this from deficient hormone release.

Nephrogenic diabetes insipidus

Lithium, electrolyte disturbance or kidney disease can make the collecting duct resistant to vasopressin, with limited response to desmopressin despite similar polyuria.

Osmotic diuresis

Glucose, urea, mannitol or diuretics cause high urine volume with substantial solute excretion rather than the inappropriately dilute urine of pure vasopressin deficiency.

Urinary frequency

Bladder pathology produces frequent small voids rather than measured large-volume urine, so documenting total output prevents an incorrect endocrine label.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Stable diagnosisConfirm hypotonic polyuriaFirst stepPersistent thirst and high urine output occur without acute dehydration.

1Measure urine volume and review glucose, electrolytes, renal function, diuretics, lithium and deliberate high fluid intake.
2Obtain paired plasma sodium or osmolality and urine osmolality under documented conditions, avoiding self-imposed dehydration.
3Refer for validated specialist dynamic testing and pituitary assessment when hypotonic polyuria remains unexplained, then image according to the biochemical and clinical question.

02DecompensationRestore water safelyKnown or suspected AVP deficiency presents with hypernatraemia, hypovolaemia, impaired consciousness or inability to drink.

1Assess volume, sodium, potassium, renal function and hourly urine output, involve endocrinology and use an appropriately monitored care setting.
2Restore circulation first with the locally selected isotonic fluid, then calculate and replace water deficit at a controlled rate with frequent sodium review.
3If excessive, inappropriately dilute urine persists after initial fluid restoration, give desmopressin 1–2 micrograms IV or IM under Society guidance and review the clinical, urine-output and sodium response before any repeat dose to avoid over-rapid correction.

03Inpatient safetyPrevent omission and overdoseA person prescribed desmopressin is admitted, fasting, vomiting or unable to self-manage.

1Reconcile exact formulation, dose and timing immediately and identify desmopressin as critical medication rather than an optional antidiuretic.
2Assess thirst, cognitive and swallowing ability, access to water, fluid prescription and urine output; agree who administers each dose.
3EscalationMonitor sodium at the frequency specified by Society and local guidance, escalating falling sodium, unquenched thirst, breakthrough polyuria or rapid weight change before repeating treatment.

Key medicines and prescribing safety1 treatment · regimens, roles and cautions

Provides selective antidiuretic activity to replace deficient AVP and reduce uncontrolled free-water loss.

Desmopressin

Continue the person's verified stable formulation and dose when safe; Society guidance lists typical oral or sublingual doses of 100–200 micrograms and intranasal doses of 10–20 micrograms. In decompensated AVP deficiency, restore fluid first, then give 1–2 micrograms IV or IM if excessive dilute urine persists and reassess before repeating.

Oral, melt, nasal and injectable doses are not equivalent. Excess treatment with fluid intake causes hyponatraemia; omission causes hypernatraemic dehydration. Nasal absorption varies with rhinitis, and intravenous dosing requires close sodium and urine monitoring.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Hypernatraemic dehydration

Unreplaced free-water loss causes weight loss, hypotension, acute kidney injury, confusion, seizure or coma, especially when drinking access or thirst is impaired.

Desmopressin-associated hyponatraemia

While desmopressin is active, excessive fluid intake cannot be excreted normally, causing water retention, headache, confusion and potentially seizure.

Inpatient medicine omission

Delayed or missed desmopressin during admission can trigger uncontrolled water loss, while uncoordinated fluid and medicine changes can shift sodium unexpectedly quickly.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track thirst, daily weight, urine volume and nocturia alongside sodium; one litre of acute retained or lost water approximates one kilogram of weight change.
In unstable resuscitation, monitor sodium at the intensive interval in the Society pathway and plot its rate of change rather than reviewing isolated results.
Review breakthrough aquaresis, formulation adherence and drinking behaviour before increasing desmopressin, because more drug can convert under-treatment into hyponatraemia.
Reassess anterior pituitary axes and MRI cause-specific follow-up after surgery, trauma, tumour or stalk disease.
Audit inpatient omissions, delayed prescriptions and unplanned fluid restriction because these are preventable sources of severe harm.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Thirst can conceal severity

A normal sodium in unrestricted ambulatory life may reflect litres of compensatory drinking. Remove water access and the same physiology can decompensate rapidly.

Cortisol masks water loss

Cortisol deficiency impairs free-water excretion. Starting glucocorticoid can unmask polyuria from AVP deficiency, so urine and sodium deserve attention after replacement.

A missed dose is diagnostic but unsafe

Breakthrough dilute urine may reveal dependence on desmopressin, yet deliberate omission during fasting or impaired drinking can precipitate severe dehydration.

Formulation is part of the prescription

Microgram and oral doses differ greatly in bioavailability. Copying only the number without route is a high-risk medicines-reconciliation error.

Postoperative patterns evolve

AVP deficiency after pituitary surgery may resolve, persist or be followed by antidiuresis. Fixed dosing without sodium and urine review can miss the transition.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing central diabetes insipidus from thirst without proving high-volume hypotonic urine.
02
Restricting water for an unsupervised diagnostic trial in someone who may lack AVP.
03
Omitting desmopressin on admission because it is misclassified as a non-essential continence medicine.
04
Giving repeated desmopressin during fluid resuscitation without observing sodium and urine response.
05
Converting between nasal, oral and parenteral formulations by using the same numeric dose.
06
Assuming normal sodium excludes disease in a person drinking continuously to thirst.