In 1981, Lugaresi and Cirignota described a group of patients who had brief nocturnal episodes characterized by tonic or dystonic spasms and violent movements (36). All had normal interictal and ictal EEGs, and all responded favorably to carbamazepine. The authors proposed three possible mechanisms for these events: i) pavor nocturnus; ii) epileptic seizure; or iii) paroxysmal dystonia. Similar cases, with many variations, have been described by others (37-40), usually under the moniker, paroxysmal nocturnal dystonia. Recent studies have suggested that the majority, if not all, of these patients have partial epileptic seizures of frontal lobe origin (39-41).
A number of investigators have described a group of related paroxysmal disorders characterized by movements that may in some instances be confused with epileptic seizures (42-45). To clarify the terminology and classification of these disorders, Demirkiran and Jankovic proposed a comprehensive classification system that used the term dyskinesia for the abnormal movements and used the circumstances that give rise to the movements as the major factor in classification (45). Based on this system, there are four major categories of paroxysmal movement disorders: paroxysmal hypno-genic dyskinesia (PHD); paroxysmal exertion-induced dyskinesia (PED); paroxysmal kinesigenic dyskinesia (PKD); and paroxysmal nonkinesigenic dyskinesia (PNKD).
In their study, Demirkiran and Jankovic reported forty-five patients with paroxysmal dyskinesia (45). One had PHD; five had PED; thirteen had PKD; and twenty-six had PNKD. Of the thirty-two patients whose attacks were witnessed by examiners, twenty-three had pure dystonia, and the other nine had dystonia in combination with chorea or ballism. These data suggest that dystonia is the most common type of movement in patients with paroxysmal dyskinesia.
Of the forty-five patients studied by Demirkiran and Jankovic, twenty-three had episodes lasting less than 5 min, a duration that could realistically be confused with epilepsy (45). None of these patients had known epilepsy, but 44% had a family history of epilepsy. The EEGs were normal in the thirty-four patients tested. Only one of the forty-five patients had brief events limited to sleep and thus may have had nocturnal partial seizures, as discussed earlier.
The mechanisms responsible for paroxysmal dysk-inesia are unknown (45). Secondary dystonia has been associated with lesions in the putamen, caudate, thalamus, and rostral brainstem. Paroxysmal dystonia has also been associated with Behcet's disease (46), subacute sclerosing panencephalitis (47), fluoxetine toxicity (48), and on assuming the upright position (49). Studies in a mutant hamster model of PNKD suggest that the abnormal movements in PNKD may be secondary to impairment of gabaergic systems (45).
Work up for paroxysmal dyskinesa has traditionally included an MRI, and if there is a suggestion of possible epilepsy, an EEG. If the MRI and EEG are normal in patients with brief nocturnal events, video-EEG monitoring may be indicated. A secondarily generalized tonic-clonic seizure following medication withdrawal is diagnostic of epilepsy.
At this time, antiepileptic agents remain the standard form of treatment for patients with paroxysmal dyskinesia (45). Other medications that have been tried include levodopa, tetrabenazine, and trihexyphenidyl. There is some evidence that patients with PKD respond better to antiepileptic medications than patients with PNKD.
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