Makindo Medical Notes

📖 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).