Imaging of his head does not reveal acute abnormalities suggesting a malignant or paraneoplastic process, and there are no concerns for ongoing seizures. An infection workup is negative. His urine toxicology is negative and blood alcohol level is 0. His sodium normalizes after 3 days of IV fluids and fluid restriction. Therefore, further tests to differentiate the causes of hyponatremia, such as urine electrolytes and urine osmolality, are not pursued.
The authors’ observations
The differential diagnosis for hyponatremia is broad in the setting of psychiatric illness. Low sodium levels could be due to psychotropic medications, psychiatrically-driven behaviors, or an underlying medical problem. Our differential diagnosis for Mr. F included iatrogenic syndrome of inappropriate antidiuretic hormone (SIADH), diabetes insipidus, or psychogenic polydipsia, a form of primary polydipsia. Other causes of primary polydipsia are related to substances, such as heavy beer intakeor use of 3,4-methylenedioxymethamphetamine (MDMA, also known as “ecstasy”), or brain lesions,1 but these causes were less likely given Mr. F’s negative urine toxicology and head imaging.
While psychogenic polydipsia is due to increased water consumption, both SIADH and diabetes insipidus are due to alterations in fluid homeostasis.2,3 Table 12-4 outlines distinguishing characteristics of SIADH, diabetes insipidus, and psychogenic polydipsia. Urine studies were not pursued because Mr. F’s sodium resolved and acute concerns, such as malignancy or infection, were ruled out. Mr. F’s hyponatremia was presumed to be due to psychogenic polydipsia because of his increased fluid intake and normalization of sodium with hypertonic fluids and subsequent fluid restriction. During this time, he was managed on the surgical service; the plan was to pursue urine studies and possibly a fluid challenge if his hyponatremia persisted.
EVALUATION Delirium resolves, delusions persist
While Mr. F is on the surgical service, the treatment team focuses on stabilizing his sodium level and assessing for causes of altered mental status that led to his fall. Psychiatry is consulted for management of his agitation. Following the gradual correction of his sodium level and extubation, his sensorium improves. By hospital Day 5, Mr. F’s delirium resolves.
During this time, Mr. F’s disorganization and religious delusions become apparent. He spends much of his time reading his Bible. He has poor hygiene and limited engagement in activities of daily living. Due to his psychosis and inability to care for himself, Mr. F is transferred to the psychiatric unit with consent from his mother.
Continue to: TREATMENT Olanzapine and fluid restriction