Many of the antiepileptic drugs are effective in controlling individual instances of reflex epilepsy. Some patients learn to avert the seizure by undertaking a mental task, for example, thinking about some distracting subject, counting, or by initiating some type of physical activity. Forster demonstrated that in certain types of reflex epilepsy, the repeated presentation of the stimulus may eventually render the trigger innocuous but this requires a great deal of time and reinforcement, which limits its therapeutic value.
This is a special type of focal motor epilepsy characterized by persistent rhythmic clonic movements of one muscle group—usually of the face, arm, or leg—which are repeated at fairly regular intervals every few seconds and continue for hours, days, weeks, or months without spreading to other parts of the body. Thus epilepsia partialis continua is, in effect, a highly restricted and very persistent focal motor status epilepticus. The distal muscles of the leg and arm, especially the flexors of the hand and fingers, are affected more frequently than the proximal ones. In the face, the recurrent contractions involve either the corner of the mouth or one or both eyelids. Occasionally, isolated muscles of the neck or trunk are affected on one side. The clonic activity may be accentuated by active or passive movement of the involved muscles and may be reduced in severity but not abolished during sleep.
First described by Kozhevnikov in patients with Russian spring-summer encephalitis, these ongoing partial seizures may be induced by a variety of acute or chronic cerebral lesions. In some cases the underlying disease is not apparent, and the clonic movements may be mistaken for some type of slow tremor or extrapyramidal movement disorder. Most patients with epilepsia partialis continua show focal EEG abnormalities, either repetitive slow-wave abnormalities or sharp waves or spikes over the central areas of the contralateral hemisphere. In some cases, the spike activity can be related precisely in location and time to the clonic movements (Thomas et al). In the series collected by Obeso and colleagues, there were various combinations of epilepsia partialis continua and cutaneous reflex myoclonus (cortical myoclonus occurring only in response to a variety of afferent stimuli).
As would be expected, a wide range of causative lesions has been implicated—developmental anomalies, encephalitis, demyelinative diseases, tumors, metabolic abnormalities, particularly hyperosmolarity, and degenerative diseases. Epilepsia partialis continua is particularly common in patients with the rare condition, Rasmussen encephalitis (see further on).
Whether cortical or subcortical mechanisms are responsible for epilepsia partialis continua is an unresolved question. The electrophysiologic evidence adduced by Thomas and colleagues favors a cortical origin; the pathologic evidence is less definite. In each of eight cases in which the brain was examined postmortem, they found some degree of involvement of the motor cortex or adjacent cortical area contralateral to the affected limbs. However, all but one of these patients also had some involvement of deeper structures on the same side as the cortical lesion, on the opposite side, or on both sides.
It is characteristic of the disorder to be resistant to treatment, often leading to the use of several antiepileptic drugs and still finding them to be ineffectual. At times, it is preferable to reduce the medications and their number in favor of producing fewer side effects. These judgments must be made in view of the disruption of daily life. Although exceptional cases may persist for a year or more, most resolve, leaving variable neurologic defects.