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Central pontine myelinolysis is characterised as symmetric and selective destruction of myelin sheath of the basis pontis. Central pontine myelinolysis often results from rapid increase of serum sodium after hyponatraemia. Patients with central pontine myelinolysis often show symptoms such as conscious disturbances, tetraparesis, and pseudobulbar palsy.1-3 We present a case of central pontine myelinolysis due to compensation of hyponatraemia, resulting in acute onset of pseudochoreoathetosis and sensory disturbances.
A 39 year old woman was submitted to a department of internal medicine of another hospital due to a long history of alcoholism, resulting in bad general condition accompanied by severe anaemia, toxic gastritis, and acute pancreatitis. She was alert without any mental disturbances. Laboratory data disclosed metabolic acidosis and hyponatraemia of 126 mmol/l. She received bicarbonate and physiological saline intravenously to compensate for the metabolic disturbances. Serum sodium increased to 136 mmol/l within 3 days. On the third day she suddenly developed severe choreoathetotic movements. Therefore she was transfered to our department of neurology. On the day of submission to our department she remained alert, but she had difficulties in swallowing and speaking. Examination of the cranial nerves showed bilateral ptosis and a dissociated nystagmus on the left side. We also found weakened corneal and pharyngeal reflexes. There was a general reduction of deep tendon reflexes and muscle tone. Muscle strength was normal. Involuntary movements were absent but angle positioning during movements was choreoathetotic. She was unaware of the position of her limbs with closed eyes. We instructed her to watch her limbs and she was then able to reach her nose with the finger. When investigating her sensitivity we found a complete loss of touchíng, vibration, and position sense in all limbs. Pinprick sensation was unremarkable in the upper limbs, whereas testing of the legs caused a painful burning sensation. Thermal sensation and sensitivity of her face were normal. We excluded tabes dorsalis and vitamin B12 deficiency by laboratory tests. Cranial CT was normal. T2 weighted MRI showed a hyperintense lesion within the pons but no extrapontine myelinolysis (figure). Within 4 weeks the subject’s symptoms had nearly disappeared. Only a slight reduction of the vibration sense in all limbs persisted. Control MRI after 4 weeks disclosed an unchanged size of the patient’s pontine lesion. At that time nerve conduction velocities and somatosensory evoked potentials, which, due to technical reasons, were only performed after the patient’s recovery, were normal.
To our knowledge this is the first reported case of central pontine myelinolysis associated with acute onset of movement disorder and isolated affection of propioceptive sensitivity.1 The appearance of parkinsonism, dystonia, or choreoathetosis in the course of central pontine myelinolysis are often looked on as symptoms of additional manifestation of extrapontine myelinolysis. The association with manifestation of central pontine myelinolysis remained speculative in some cases of delayed onset of movement disorders after central pontine myelinolysis.1 By contrast our patient showed an acute onset of pseudochoreoathetosis after manifestation of central pontine myelinolysis and MRI imaging in our subject disclosed no signs of extrapontine myelinolysis.
Our patient additionally showed an isolated loss of propioceptive sensation. Disturbances of sensation are described as less severe symptoms of central pontine myelinolysis. Silver et al 2 described an association of sensory ataxia and affection of vibration and position sense, but with reduced pinprick sensation.2 This case may imply a further extension of the pontine lesion or a possible extrapontine lesion, not detectable on MRI.2 Defebre et al reported two cases of central pontine myelinolysis with isolated affection of deep sensation.3 Isolated affection of the medial lemniscus of the brain stem or thalamic infarction may cause sensory ataxia and disturbances of deep sensitivity resulting in choreoathetotic movements.4 5 Therefore, we speculate that our patient’s pontine lesion caused sensory ataxia and subsequent pseudochoreoathetosis, because the movement disturbances appeared without delay after the onset of sensory defects. Moreover, the loss of propioceptive sensitivity with spared thermal and pain sensation implies an isolated alteration of the medial lemniscus by sparing the spinothalamic tract.4 This finding suggests a lesion with a pontine site. We found no extrapyramidal lesion by MRI in our patient. In conclusion we hypothesise that the pontine lesion itself may be a possible cause of our patient’s pseudochoreoathetotic movements.
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