A 48-year-old previously well woman presented to the emergency department with severe headaches and depressed conscious state, Glasgow Coma Score (GCS) of 12 (E4V3M5), one day after she received her second Pfizer COVID-19 vaccination. She was not on prescribed medications or over the counter supplements. On examination, she was afebrile with normal oxygen saturation, blood pressure 125/76 mmHg, heart rate 70/min. An isolated right lateral gaze palsy and reduced GCS prompted a referral to the Stroke Team. Computed tomogram brain (CTB) and angiographic imaging studies did not reveal cerebrovascular accident, however cerebral oedema was noted (Fig. 1).
Laboratory investigation revealed a serum sodium of 113 mmol/L, potassium of 3.4 mmol/L, urea 3.5 mmol/L, and serum osmolality of 266 mmol/kg. TSH, random cortisol, serum glucose, calcium and C-reactive protein levels were normal. Lumbar puncture revealed a clear, bland cerebrospinal fluid (CSF) with normal cell count and mildly elevate protein (0.63 g/L, reference range < 0.45 g/L)). Urine chemistry was not available on admission. Insertion of a urinary catheter revealed urinary retention of 1.4 L, with an urine osmolality of 81 mmol/L and a urine sodium of < 20 mmol/L.
The patient was commenced on empirical treatment for meningoencephalitis (benzylpenicillin, aciclovir) concurrently with normal saline (total of 350 ml at a rate of 100 ml/h) from presumptive polyuric hypovolemia. In ICU, GCS further decreased to 10 (E3V2M5), the patient became polyuric with an output up to 910 ml/h, and underwent rapid correction of serum sodium to 127 mmol/L four hours post baseline presentation of 113 mmol/L. The intravenous fluid therapy was altered to dextrose 5 % matched to the previous hours urine output plus 50 ml/h. Serum sodium continued to over correct to 137 mmol/L seven hours after presentation.
The patient's neurological symptoms completely resolved 13 h post presentation with a serum sodium of 142 mmol/L the next morning. She recalled thirst and increased fluid intake on day of admission, but denied consumption of greater than 2.5 L/day. Antiviral therapy was ceased when CSF polymerase chain reaction (PCR) was negative for herpes, entero and adenoviruses. The patient was also negative for COVID-19, influenza A, influenza B and Respiratory Syncytial Virus. The clinical impression was she had developed acute hyponatraemia with spontaneous and rapid correction. The confusion was attributed to cerebral oedema due to severe hyponatraemia and possible seizure. The patient remained well after 4 days and was discharged without any manifestation of central pontine myelinolysis. Additional biochemical results became available which included an admission copeptin level of 4.4pmol/L which decreased further to 2.1 pmol/L four hours after the admission bloods.