Polydipsia-hyponatraemia syndrome : epidemiology, clinical features and treatment.

The polydipsia-hyponatraemia syndrome (PHS) occurs in about 5 to 10% of institutionalised, chronically psychotic patients, 80% of whom have schizophrenia. Major clinical features are polydipsia and dilutional hyponatraemia. Complications of PHS include delirium, generalised seizures, coma and death.Nonpharmacological interventions are fluid restriction, diurnal bodyweight monitoring, behavioural approaches, and supplemental oral sodium chloride administration. These interventions require an experienced and dedicated multidisciplinary staff.A number of pharmacological treatments have been assessed for PHS including the combination of lithium and phenytoin, demeclocycline, propranolol, ACE inhibitors, selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors, typical antipsychotic drugs, clozapine and risperidone. Of these agents, the most promising are the combination of lithium and phenytoin, and clozapine.Integrated treatment requires a highly informed multidisciplinary staff, meticulous monitoring of diurnal weight gain and serum sodium level, and careful record keeping. Acute interventions of observation by trained staff, fluid restriction, water-free areas and supplemental sodium chloride administration are based on diurnal weight gain employing a monthly weight chart and a base weight method. Intravenous hypertonic saline is used briefly and administered in a highly controlled manner when patients with PHS present with generalised seizures and coma. Long term strategies include behavioural interventions and the combination of lithium and phenytoin, and clozapine.