Psychogenic Polydipsia
📖 About
- 💧 Psychogenic polydipsia is excessive water intake driven by underlying psychiatric or behavioural causes.
- ⚠️ Can lead to hyponatraemia and serious complications such as seizures, coma, or death if untreated.
- 🧠 Most often seen in psychiatric inpatients (schizophrenia spectrum disorders).
🦠 Aetiology
- Strongly associated with schizophrenia, but also anxiety, depression, and obsessive-compulsive disorder (OCD).
- May be related to stress, institutionalisation, or learned behaviours.
- Sometimes linked with antipsychotic side effects (e.g. dry mouth from anticholinergic drugs).
🔍 Clinical Features
- Excessive and compulsive drinking behaviour (often >3–4 L/day).
- Polyuria (passing large volumes of dilute urine).
- Confusion, agitation, or seizures if hyponatraemia develops.
- Symptoms resolve with restriction of fluid intake (water deprivation confirms diagnosis).
- Common in long-term psychiatric inpatients, where supervision reveals the behaviour.
⚖️ Differential Diagnoses
- 🧪 Diabetes insipidus (central or nephrogenic) – inability to concentrate urine despite dehydration.
- 💧 Primary polydipsia (non-psychogenic) – excessive water intake without psychiatric cause.
- 🧠 SIADH – hyponatraemia due to inappropriate ADH secretion, not fluid overload behaviour.
🧪 Investigations
- 🩸 Serum U&Es: Hyponatraemia, low serum osmolality.
- 💦 Urine Osmolality: Typically <100 mosm/kg (very dilute urine).
- 🚱 Water Deprivation Test: Differentiates psychogenic polydipsia from diabetes insipidus (patients with psychogenic polydipsia concentrate urine normally when restricted).
- 🔎 Rule out drug-induced causes (e.g. SSRIs, carbamazepine) that may worsen hyponatraemia.
💊 Management
- 🧠 Treat the psychiatric disorder: Optimise antipsychotic or antidepressant therapy. Clozapine has evidence for reducing polydipsia in schizophrenia.
- 📉 Fluid restriction: Gradual, supervised water intake restriction (to prevent rapid sodium shifts).
- 👩⚕️ Behavioural therapy: Education, structured routines, and monitoring by staff or carers.
- 🧪 Medical monitoring: Regular checks of sodium, serum osmolality, and urine output to prevent hyponatraemic crises.
- 🚨 Severe symptomatic hyponatraemia (confusion, seizures): admit to hospital, consider cautious hypertonic saline under strict ICU monitoring.
📚 Teaching Tip
💡 Always think of psychogenic polydipsia in psychiatric inpatients with recurrent unexplained hyponatraemia.
Differentiation from SIADH is essential — check urine osmolality:
- 👎 SIADH → urine concentrated (high osmolality).
- 👍 Psychogenic polydipsia → urine very dilute (low osmolality).
