**3.1 Psychotic illnesses**

One of the most common psychotic illnesses that affect serum sodium is schizophrenia. As defined by DSM-5 [1], schizophrenia is characterized by two of more of the following symptoms including delusions, hallucinations, disorganized speech, grossly disorganized or catatonic behavior, and negative symptoms (i.e. diminished emotional expression) that are present for a significant portion of a 1-month period and continuous signs of disturbance in functioning level present for at least 6 months. Patients with schizophrenia can experience primary psychogenic polydipsia (PPD), characterized by an increase of fluid intake along with excretion of excessive amounts of dilute urine exceeding 40–50 mL/kg of body weight [8]. It is hypothesized that this occurs in patients with schizophrenia due to elevated levels of dopamine that stimulate the thirst center [8]. In patients with schizophrenia, polydipsia prevalence is estimated at 6–20%, and complications can include not just hyponatremia but rhabdomyolysis as well [9]. Severe water intoxication has also been reported in a patient with delusional skin infestation leading to hyponatremia [10].
