A 76-year-old Asian male with a history of hypertension, type II diabetes mellitus (T2DM), and transient ischemia attack (TIA) presents with cough, fatigue, and headache for four days. A chest radiograph revealed a right middle lobar opacity with concern for community-acquired pneumonia (CAP). IV antibiotics were started for CAP coverage and the patient was admitted for monitoring. Complete blood count (CBC) and comprehensive metabolic panel (CMP) were within normal limits, showing a sodium of 136mmol/L and a creatinine of 0.74 mg/dL. On hospital day five, creatinine was found to be 1.12 mg/dL and 1L of normal saline was given as bolus to address prerenal acute kidney injury (AKI). Over the next two days, an additional 2L of normal saline was administered, which resulted in a return of creatinine to baseline. Upon finishing antibiotics on hospital day seven, the patient’s CAP resolved and was discharged to home. Two weeks later, the patient returned with his wife, who reported that he was more somnolent than usual and was slower to react. On presentation, the patient was alert and oriented but visibly fatigued. He denied dysarthria, dysphagia, or paresis. CBC and CMP were unremarkable and consistent with baseline, showing a sodium of 138mmol/L. MRI of the brain showed hyperdensities and features consistent with mild central pontine myelinolysis. Relowering of serum sodium was not attempted due to prolonged duration since symptom onset. The patient was subsequently discharged with instructions to follow-up with neurology.

Osmotic Demyelination Syndrome (ODS) classically occurs due to rapid over-correction of serum sodium by more than 8 mEq/L over a 24-hour period in the setting of brain adaptation to hyponatremia. Brain hypoxia and diabetes mellitus has also been posited as risk factors for ODS, although the mechanisms are still under investigation. In this case, despite being eunatremic, a patient with a history of T2DM and TIA received IV fluid boluses during his hospital course and developed ODS. A complex interplay of these risk factors may have ultimately resulted in this unorthodox case of eunatremic ODS. Clinicians should carefully consider the possibility of ODS when repleting volume or electrolytes in high-risk patients.