Synopsis
Distinguish impaired thirst, primary polydipsia and broader hypothalamic dysfunction, then build supervised water, endocrine and neurobehavioural safety plans.
- Thirst and AVP secretion are separate hypothalamic responses to tonicity; losing one but not the other creates distinctive risk.
- Adipsia means absent or inadequate thirst despite a physiological stimulus and is particularly dangerous when central AVP deficiency coexists.
- Primary polydipsia suppresses AVP appropriately and produces very dilute urine; chronic excess intake can blur dynamic testing by reducing renal concentrating capacity.
- Before attributing thirst to behaviour, exclude hyperglycaemia, hypercalcaemia, hypokalaemia, diuretics, kidney disease and true AVP deficiency.
- Hypothalamic lesions may also disturb appetite, weight, temperature, sleep-wake rhythm, autonomic regulation, memory, behaviour and several pituitary axes.
- A supervised fixed-fluid and desmopressin plan may be necessary when thirst is unreliable; telling an adipsic patient simply to drink to thirst is unsafe.
- Psychiatric illness and medicines can contribute to polydipsia, but diagnostic language must remain non-stigmatising and follow measured physiology.
- Rapid weight change, urine output and sodium trend often reveal water imbalance earlier than a patient with cognitive or thirst impairment can report symptoms.
Investigation priorities
Quantify drinking, nocturia and urine output against timing of symptoms, medicines and caregiver support.
Management branches
Thirst, high intake, urinary frequency or recurrent dysnatraemia lacks a clear cause.
- Measure true urine volume and construct a timed intake-output history with family or carers where insight or memory may be limited.
- Check paired plasma and urine tonicity plus glucose, calcium, potassium, kidney function and relevant medicines before imposing fluid change.
- Refer equivocal hypotonic polyuria for supervised dynamic testing, explicitly documenting whether thirst rose appropriately during the stimulus.
Key medicines
Desmopressin in adipsic AVP deficiencyUse the formulation-specific fixed regimen designed by the specialist centre, coordinated with a prescribed daily water intake and weight or sodium adjustment rule rather than unsupervised symptom dosing.Both omission and over-treatment can be rapidly dangerous. Cognitive impairment increases dosing error, formulations are not interchangeable, and illness or altered intake requires immediate plan review.