Central pontine myelinolysis (CPM) is an uncommon neurological syndrome that is usually related to the rapid restoration of a previous hyponatraemia. Although the most frequent location of CPM injury is the pons, it is now designated osmotic demyelination syndrome (ODS) because, as well as in the brainstem, these injuries can be observed in other parts of the central nervous system (CNS)-for example, the thalamus, subthalamic nucleus, external geniculate body, putamen, globus pallidum, internal capsule, white matter of cerebellum and the deep layers of the brain cortex. However, an exhaustive search of the literature (MEDLINE 1967(MEDLINE -2007 has revealed no case report of peripheral nervous system (PNS) demyelination secondary to severe hyponatraemia.Experimental models of hyponatraemia have shown a marked fall in brain levels of several organic osmolytes during the first few hours after the metabolic insult, followed by a slow restoration over several days. 1 The rapid correction of hyponatraemia can lead to low brain concentrations of amino acids and creatine, even after serum sodium correction, producing a net shrinkage of the brain. A high sodium concentration without adequate concentrations of organic osmolytes may predispose the brain to osmotic injury.
CASE REPORTWe present the case of a 35-year-old woman with a history of active alcohol abuse and no previous polyneuropathy. Three months before hospital admission, she presented with an intermittent diffuse encephalopathy, changes in behaviour and consciousness, and visual hallucinations. One week before admission, she became unable to walk and suffered a marked deterioration in consciousness, with an elevated consumption of up to 6-10 litres of liquids daily. A full evaluation on her admission to the Emergency area included analytical screening for the most frequent toxic metabolic encephalopathies and brain CT. Results indicated that the sole cause of her neurological deterioration was a plasma sodium concentration of 97 mg/dl with simultaneous urinary hypo-osmolarity. She was diagnosed with hyponatraemic encephalopathy and treated with oral liquid restriction and intravenous infusion of 0.9% normal saline or 7% hypertonic saline. After 2 days, her serum sodium was 135 mg/dl, an estimated rate of increase of 0.79 meq/l per hour.Over the next few days, she developed a progressive flaccid tetraparesis (2-3/5 in distal vs. 4/5 in proximal muscle groups), with normal ankle and knee reflexes, bilateral Babinski signs and mild distal amyotrophies in both upper and low extremities. Neuropsychological examination at this time showed an anarthric mutism with acceptable comprehension of verbal language, affective lability but relatively normal mental status. She had poor left conjugate gaze and no perimetric defects. Low cranial nerve examination was consistent with bilateral velopalatine paralysis. A continuous myoclonic left facial jerk was observed. The remainder of the neurological examination was normal.Basic haematological and coagulation studies and bioc...
