Hyponatremia associated with demyelinating disease of the nervous system.

A 63-year-old man was diagnosed with periodontitis and underwent tooth extraction. Several days later, he suffered a high fever, ischuria, a change in personality, and disorientation. A urologist examined him and found severe hyponatremia (117 mEq/L), and he was then transferred to our hospital. On admission, physical findings revealed dysfunction of the bladder and bowel, altered mental status, and hypovolemia. Blood chemistry showed serum sodium of 120 mEq/L, a serum urate of 1.4 mg/dL, urinary Na of 61 mEq/L, and fractional urate excretion of 16 %. Examination of the cerebrospinal fluid (CSF) showed monocytosis. Magnetic resonance imaging (MRI) of the brain and spinal cord showed multiple lesions characterized by hyperintensity on T2-weighted sequences, suggesting demyelinating disease. His sodium concentration normalized 3 days after volume replacement therapy, and his altered mental status along with the dysfunction of the bladder and bowel were promptly improved after the initiation of high-dose glucocorticoids. Additionally, the abnormal lesions on MRI markedly decreased. This clinical course led to the likely diagnosis of acute disseminated encephalomyelitis (ADEM). Hyponatremia in neurologically injured patients is usually attributed to the syndrome of inappropriate antidiuretic hormone (SIADH) or cerebral salt-wasting syndrome (CSWS). In the present patient, the uric acid level remained low and uric acid excretion remained elevated despite correction of the hyponatremia, which suggested CSWS. The differentiation of CSWS from SIADH is difficult but critically important due to the fact that the disorders are managed differently. Coexistence of ADEM and CSWS has rarely been reported.