Abstract
Fabisiak et al. (1) report a case of central pontine myelinolysis (CPM) in a patient taking lithium. CPM was previously mentioned in this journal as a likely consequence of a rapid fall of serum lithium levels after a gradual rise to high levels (2, 3). Such rapid lithium fall is associated with neurological injury (4). The physiological background is that 1) intracellular sodium levels are about 7 meq/L, 2) lithium displaces sodium intracellular 1 and 3) CNS intracellular lithium levels are 50% above serum levels. Accordingly, a rapid decrease in lithium levels might cause intracellular hyponatremia, which would be rapidly corrected because there is no actual shortage of sodium.