Keywords
osmotic demyelination - hyponatremia - hypokalemia
Introduction
Central pontine myelinolysis occurs due to rapid correction of hyponatremia. Interestingly,
osmotic demyelination has been described with sodium levels within normal limits and
hypokalemia as well.[1]
[2] Osmotic demyelination at extrapontine sites with or without pontine involvement
has also been described.[3] There are few studies with sequential magnetic resonance imaging (MRI) to understand
the evolution of the syndrome.
A patient with hyponatremia and hypokalemia is presented, who as a result of osmotic
demyelination had sequential appearance of extrapontine lesions, followed by resolution
of the same.
Case Report
A 57-year-old man, a teetotaller, presented with spastic quadriparesis of 8 months,
duration. He underwent discoidectomy and bone grafting for cervical disc prolapse.
The patient was discharged with power of 4+/5 in all four limbs. Ten days post discharge,
the patient sustained a fall and was readmitted with quadriplegia. Repeat MRI showed
graft displacement with residual/recurrent compressive myelopathy. A redo bone grafting
and plating was done. Postoperatively, his quadriparesis improved to 3/5; however,
he required ventilation for spells of bradypnoea.
Postoperatively, electrolyte panel revealed hyponatremia (sodium 102 mmol/L) and hypokalemia
(potassium 1.9 mmol/L). Hyponatremia was corrected with 300 mL of 3% sodium chloride
infusion over 6 hours and 40 meq of potassium was supplemented intravenously. After
15 hours, the sodium and potassium levels were 115 and 2.1 mmol/L, respectively. By
the third postoperative day, electrolyte levels had normalized. He was weaned off
ventilator on the fifth postoperative day. However, he became quadriplegic with intact
extraocular movements suggestive of locked in syndrome, developed persistant lip smacking
movement followed by a generalized tonic–clonic seizure.
MRI brain done on the eighth postoperative day for a clinical diagnosis of locked-in
syndrome revealed no lesions in the pons but extensive lesions on T2 weighted and
flair images in bilateral caudate nuclei, putamina, thalami, coronae radiate, periventricular
white matter, and hippocampi ([Fig. 1]). A diagnosis of extrapontine myelinolysis was made. The patient was treated symptomatically
with mechanical ventilation and anti epileptic drugs. The patient recovered completely
over 8 weeks. MRI after 2 months, interestingly, revealed new lesions in the pons,
with partial resolution of the previous lesions in the extrapontine locations. During
follow-up after 6 months, the patient showed improvement in quadriparesis to 4+/5
and repeat MRI showed complete resolution of myelinosis ([Figs. 2] and [3]).
Fig. 1 Magnetic resonance imaging (flair images) on day 8 showed extensive extrapontine
myelinolysis.
Fig. 2 Magnetic resonance imaging after 6 months showed resolution of all lesions.
Fig. 3 Magnetic resonance imaging after 6 months showed resolution of all lesions.
Discussion
The theories explaining the etiopathogenesis of osmotic demyelination have undergone
frequent revision. Initially described in alcoholic cirrhotics, it was realized later
that too rapid correction of hyponatremia possibly leads to osmotic shrinkage of axons,
inducing demyelination. Coexisting hypokalemia is believed to increase the risk of
myelinolysis in patients with rapidly corrected hyponatremia.[2] The exact mechanism of this interaction is not understood. Our patient highlights
the compounding role played by persistent hypokalemia in precipitating myelinolysis.
MRI on the eighth postoperative day had revealed extensive osmotic demyelination in
the brain, sparing the pons. After 2 months, when the patient had completely recovered,
MRI paradoxically revealed evidence of central pontine myelinolysis too. There are
few reports in literature of such sequential development of lesions.[4] Delayed clinical manifestations, especially with extrapyramidal syndromes, from
10 days 5 months after osmotic demyelination at extrapontine locations have been reported.[5] Lesions on MRI are known to present up to 14 days after osmotic dysregualtion. However,
sequential new lesions on MRI, in clinically improving patients have not been described.
The lack of correlation between the clinical course and MRI findings is well known.
Our patient with a locked in syndrome had no demonstrable lesion in the pons. The
prognosis, considered previously to be grave, has improved with better understanding
and management of the disorder.[6] Despite the extensive lesions, and a clinical presentation initially confused by
the cervical myelopathy resulting in a delay in diagnosis, our patient made complete
recovery.
This case underlines the fact that there are factors other than the rapid correction
of hyponatremia, such as persistent hypokalemia that possibly contributes to the course
of this syndrome. There is a need for more sequential MRI studies in patients with
osmotic demyelination in order to shed light on this queer syndrome. With appropriate
treatment, the prognosis is favorable.
