Epilepsia partialis continua (EPC) is a rare presentation of epilepsy, but its recognition is important because it may be the harbinger of very serious disease. EPC was described by the International League Against Epilepsy as involving nonprogressive localized partial motor seizures followed by myoclonus at a later point in time.¹ It is characterized by sustained and persistent repetitive focal motor activity, usually described as clonic or myoclonic in nature, typically involving a limited number of muscle groups. Both agonist and antagonist muscle groups can be involved, with any frequency, and it can persist to some degree in sleep. The face, shoulder, arm, and hand are most commonly affected (Videos 27-1, 27-2, 27-3, 27-4, and 27-5). The movement may have an arrhythmic character. Some patients report seizures worsening during activities, such as moving to pick up an object. In these cases, seizure exacerbations as the hand nears the target may be suggestive of an intention tremor, but the larger amplitude in EPC usually distinguish the two types of movements.

EPC may be due to a number of conditions (Table 27-1). Inflammatory causes comprise some of the best-known etiologies of EPC. Infectious agents and syndromes associated with EPC are primarily viral (Epstein-Barr virus, cytomegalovirus, JC polyomavirus of progressive multifocal leukoencephalopathy, human immunodeficiency virus, tick-borne encephalitis virus, and measles virus in subacute sclerosing panencephalitis), although bacterial causes (tuberculosis, cat scratch disease, and pertussis), fungal disease (cryptococcosis), and prion diseases (Creutzfeldt-Jakob disease) also have been seen.^2,3 Rasmussen syndrome is an inflammatory condition that primarily affects children and is discussed in detail later in this chapter, along with the relationship of EPC to Kozhevnikov encephalitis. Other associations are multiple sclerosis, lupus erythematosus, and Sjögren syndrome. Paraneoplastic syndromes, which also are mediated by antibodies, may be a cause. One oncological association is gliomatosis cerebri.

Noninflammatory causes include structural abnormalities, such as trauma (Figure 27-1), malformations of cortical development, infarctions, and, rarely, tumors. Causative neoplastic abnormalities include gliomatosis cerebri, astrocytomas, lymphomas, and hemangiomas.^3,4 In addition, iatrogenic causes have been reported, including a subdural hematoma after subdural grid placement and metrizamide cisternography. Metabolic causes associated with EPC include ketotic and nonketotic hyperglycemia, mitochondrial disorders, Kuf disease, and specific genetic syndromes, including Friedreich ataxia.

The differential diagnosis of EPC can include juvenile myoclonic epilepsy, one of the progressive myoclonus epilepsies, or movement disorders, such as myoclonus, polymyoclonus, and tremors. Juvenile myoclonic epilepsy frequently presents in adolescents with generalized tonic-clonic seizures; on further questioning, patients may report early morning myoclonus. On occasion, the myoclonus is what brings the patient to the physician’s attention, although generalized seizures are a more frequent initial presentation. Progressive myoclonus epilepsies are associated with multiple types of seizures, developmental regression, and myoclonus. Generally, movement disorders are less common in sleep, which makes EPC a more likely diagnosis if the movement persists during sleep. Furthermore, myoclonus and tremors typically do not have the arrhythmic character of EPC. Electroencephalography (EEG) may be helpful in the diagnosis, as the epilepsies with myoclonus have specific EEG abnormalities that differ from those related to EPC.

Because EPC is believed to represent focal epileptiform activity, some might expect clear routine scalp EEG findings.³ However, scalp EEG and electrocorticography in EPC may be normal, presumably because of the potentially small area of cortex involved, the depth and orientation of the functionally abnormal tissue, and the asynchronous activity of the neurons involved.^5,6 However, clear focal spikes and periodic lateralized epileptiform discharges (PLEDs) over motor regions have been recorded in some cases, and techniques such as jerk-locked back-averaging or recording from depth electrodes may detect epileptiform activity in the cortex.⁵ Back-averaging generally involves multichannel EEG recording; with jerk-locked back-averaging, a jerk occurs, and an average number of responses before and after the jerk is obtained.³ Responses at expected latencies indicate involvement of the corticospinal tract, and there can be associated changes in somatosensory evoked potentials.³ Enhanced focal cortical excitability can be seen in many of the diseases discussed above, probably through known pathways that involve reciprocal innervations of the cortex and subcortical structures. If a lesionectomy or focal cortical resection is performed for EPC due to an isolated focal process, electrocorticography can demonstrate epileptiform activity in a limited region of interest (Figure 27-1).³

Treatment of EPC is notoriously difficult and is usually targeted at the underlying disorder. Because EPC movements associated with the hand and arm can interfere with activities of daily living, occupational therapy may be useful for helping patients adapt to basic activities and tasks involving dexterity. One example is the implementation of left-sided steering and foot controls for driving in a patient with EPC that affects the right arm and leg. Another example is training a patient to write and to brush his or her teeth with the unaffected hand. Similarly, physical therapy may be useful for assisting with ambulation issues.

Rasmussen syndrome, first described by Theodore Rasmussen in 1958, is one of the most recognized causes of EPC, and is the most common cause of EPC in the pediatric population. Bancaud et al. subclassified EPC into two forms. The first was nonlesional and would fit more closely with Kozhevnikov encephalitis, a Russian spring-summer presumed encephalitis caused by a tick-borne flavivirus. The second form was associated with Rasmussen syndrome.⁷ Less than half of all patients with Rasmussen syndrome have EPC, but its common identification with EPC, particularly in children, justifies its consideration here.

Clinical Description

Rasmussen syndrome is characterized by refractory focal-onset epilepsy and progressive hemiparesis contralateral to the involved hemisphere. It is almost always unilateral; there have been a few cases reported with bilateral involvement, but this clearly is highly exceptional. Decline of function reflects involved areas, including cognitive function, sensory disorders, visual field loss, or movement disorders, such as tremors and dystonic posturing. EPC is seen in about half of all patients with Rasmussen syndrome. When it is seen, it does not follow the typical jacksonian march seen in other partial-onset motor seizures. In fact, the jerking may appear in the face, then the leg, and then the hand, reminiscent of a seemingly random pattern of activation (Videos 27-2 and 27-3). This likely represents the patchy distribution of lesions noted when pathologic specimens are examined (see below).