July 24, 2007

Post-Hypoxic Movement Disorders

A healthy young male was struck by lightning in the front yard of his home. He developed ventricular fibrillation and was eventually resuscitated. An unclear period of anoxia produced ischemic lesions (DWI - positive) in his basal ganglia bilaterally. He spent an extended period of time in an acute care hospital. Neurology was reinvolved in his care three months after his initial presentation for full body jerks (myoclonus), rigidity, and a persistently open mouth with tongue dyskinesia. These three symptoms had all worsened after his valium was decreased by 50%. His physical exam reveal flexor posturing of the upper extremities with increased tone to the point of rigidity throughout. His hypoxic-ischemic injury has left him without the ability to speak or follow commands. He is able to track consistently with his eyes and move his neck and head toward a stimulus.

This patient's severe disability and seeming movement disorders led to the following paper. Some aspects of it are presented below.

Venkatesan A, Frucht S. Movement Disorders after Resuscitation from Cardiac Arrest. Neurol Clin 24 (2006) 123-132.

After hypoxic-ischemic injury, parkinsonism, dystonia, chorea, tics, athetosis, tremor, and myoclonus have all been described. Post-hypoxic myoclonus (PHM), which can be seen acutely or as a long-term sequela, may be focal, multifocal, or generalized. Acute PHM is characterized by severe, generalized myoclonic jerks in deeply comatose patients. The prognosis associated with acute PHM is extremely poor. The best evidence points to diffuse cortical damage as the cause. Treatment usually consists of IV sedation. Chronic PHM (Lance-Adams Syndrome) is characterized by action myoclonus involving the limbs, stimulus sensitivity, and negative myoclonic jerks. Localization is both cortical and subcortical.

    "It seems that cortical myoclonus is much more common in chronic PHM than subcortical myoclonus, the latter of which tends to cause violent jerks of the proximal limbs and trunk."
First-line treatments are Clonazepam, valproate, and piracetam. Baclofen, diazepam, ethanol, methysergide, GHB, and levetiracetam have also been used.

Of greater importance to this case are the movement disorders caused by damage to the basal ganglia. There seems to be a spectrum of post-hypoxic dystonic and akinetic-rigid syndromes. The akinetic-rigid syndrome developing within three months of the hypoxic event is characterized by "bradykinesia, micrographia, axial and appendicular rigidity, resting or postural tremor, and marked postural instability." Treatment responses are dismal. Those with a dystonic syndrome areyounger than those with a more akinetic-rigid syndrome. Case series suggest that dystonic syndromes predominate in those with putaminal lesions, while the akinetic syndrome occurs in those with pallidal lesions. The mechanism of preferential damage to the basal ganglia has fallen into two camps: the vascular hypothesis which states that there is selective hypoperfusion to the basal ganglia during a hypoxic event; and the metabolic hypothesis which postulates that high metabolic requirements result in selective hypoxic damage.
    "Regardless of the mechanism, it seems that damage to the basal ganglia with preservation of the pyramidal system is a pathologic correlate of delayed posthypoxic dystonia or akinetic-rigid syndromes."

1 comment:

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