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Paroxysmal exercise induced dystonia is a rare disorder classified as one of the paroxysmal dyskinesias.1 2 In this condition patients develop dystonia, mostly involving their feet, after prolonged exercise, usually walking or swimming.1-3Treatment response is poor to both antieplileptic drugs and drugs given for dystonia—for example, anticholinergic drugs, muscle relaxants, or acetazolamide.3
We recently noted the dramatic benefit of unilateral pallidotomy in completely abolishing attacks of paroxysmal exercise induced dystonia of the contralateral foot in one patient.
This 47 year old woman was followed up over 2 years for a 10 year history of attacks of dystonia affecting her right foot, induced by exercise. At onset the attacks were mild and were induced by walking long distances. During an attack her right foot would invert for a few minutes making it difficult for her to continue walking or stand. The attack would subside within 2–3 minutes on resting. Two years after onset the attacks subsided and she was attack free for 3–4 years. Four years ago the attacks returned and got progressively worse, increasing in frequency and intensity. Over the past 2 years she could have an attack on walking even 10–15 steps. The attacks in the past few years not only made her right foot to in turn as before but caused her to fall as the right leg would rise up in the air and flex at the knee and hip and there would be some involvement of the trunk causing her spine to twist to the left. Recently the toes of the left foot were also noted to curl up during attacks. She would never lose consciousness and the attacks would last 1–2 minutes and then subside. They never occurred in sleep. Interictally the neurological examination was normal although posturing of the right foot could be induced by repeated prolonged passive flexion-extension movements of the right ankle. More recently she also began to have occasional spontaneous attacks. Investigations including repeated MRI of the head and spine were normal as were tests for Wilson’s disease and other causes of secondary dystonia. Examination of CSF gave normal results and disclosed no oligoclonal bands. The patient was negative for the common mitochondrial mutations. An EMG/nerve conduction study detected no evidence of a peripheral neuropathy and somatosensory evoked potentials were normal. Polymyography confirmed cocontraction of agonists and antagonist muscle pairs in the right leg during an attack supporting an organic basis for the dystonia. Surface EEG during an attack and interictally disclosed no abnormality. The patient was tried on a variety of treatments including baclofen, levodopa, benzexhol, tetrabenazine, and acetazolamide without benefit. Different antiepileptic drugs given individually or in combination (1g sodium valproate with 1 g carbamazepine, and 2 m clonazepam a day) also did not help. The failure of the medical treatment and the frequency of up to 10 or more attacks a day made normal functioning impossible for the patient and therefore a surgical option was considered particularly as the attacks were mainly unilateral. With the consent of the patient a left posteroventral medial pallidotomy was carried out as in a previously described technique.4 She made an uneventful recovery and had no neurological complications. Immediately after operation the attacks of exercise induced dystonia had ceased completely having occurred more than 10 times a day immediately before the operation even on walking 10–15 steps. At the end of 6 months follow up she had been attack free, apart from occasional minor spasms of her left foot on exercise, despite normal activities; anticonvulsant treatment was gradually being withdrawn.
This is the first example of the usefulness of pallidotomy in a patient with any form of paroxysmal dyskinesia. Pallidotomy and more recently pallidal stimulation are currently being used as surgical techniques for advanced Parkinson’s disease in patients with complications of levodopa treatment.5 These procedures are particularly helpful in abolishing the levodopa induced dyskinesias.5Pallidotomy has also been found beneficial in patients with generalised dystonia6 and recently a unilateral pallidotomy was reported to produce bilateral benefit in one patient with tardive dyskinesia.7
Given the improvement in our patient a unilateral pallidotomy could be considered as a treatment option in patients with stereotyped paroxysmal attacks as occur in paroxysmal exercise induced dystonia and the other paroxysmal dyskinesias such as paroxysmal non-kinesigenic dyskinesias in which treatment is often unsatisfactory.2 A bilateral procedure could be considered in patients with bilateral attacks such as patients with paroxysmal non-kinesigenic dyskinesias who are unresponsive to drug treatment as bilateral pallidotomy seems to improve patients with generalised dystonia.6