LessonPrimary polydipsia occurs in up to 25% of patients with chronic psychiatric disorders (especially schizophrenia), related to the disease, its treatment or both. Urine output fails to match intake >10 L/day and water intoxication may develop. Rhabdomyolysis is a rare complication of hyponatremia, and an acute anterior compartment syndrome of the leg, an emergency, may be very rarely associated.