CSF glucose: a memory of what the blood has forgotten

Hypoglycaemia as the cause of unwitnessed coma may go unrecognised when the hypoglycaemia has already been partially corrected. A woman in her early 60s was found unresponsive after several days of heavy alcohol intake and poor oral intake. Emergency services had given intravenous 50% glucose; on arrival, her blood glucose was only mildly low (3.1 mmol/L (56 mg/dL)). MR scan of the brain showed cortical-predominant signal change with cortical hyperperfusion. Lumbar puncture 1.5 hours after arrival showed profound hypoglycorrhachia (cerebrospinal fluid (CSF) glucose 0.8 mmol/L (15 mg/dL)) without pleocytosis or protein elevation; multiplex CSF PCR and cultures were negative. The CSF finding suggested severe prehospital hypoglycaemia and supported a diagnosis of hypoglycaemic encephalopathy despite non-specific early imaging and electrophysiology. She required tracheostomy and remained severely disabled at 6 months. Profoundly low CSF glucose with non-inflammatory CSF can be an objective, time-integrated marker of antecedent severe hypoglycaemia and can help attribute unwitnessed coma to hypoglycaemic encephalopathy when plasma glucose at presentation is misleading.