The cerebellar seizures of Hughlings Jackson

Cerebellar seizures as a clinical entity.

At the time Jackson’s paper was published, the understanding of epilepsy was undergoing a revolutionary change.7 In the early years of the 19th century, Marshall Hall8 postulated that the “seat of epilepsy” was in the spinal cord, and he further postulated that epilepsy was due to heightened activity within the spinal reflex arc. Brown–Sequard9 noted that peripheral stimuli within the so-called “epileptogenic zone” of the face and neck often activated excitatory mechanisms reflexively in the medulla oblongata, which in turn induced cerebral vasospasm that caused unconsciousness during seizures. Other authors such as Nothnagel,10 van der Kolk,11 and Kussmaul and Tenner12 similarly postulated a brainstem and/or spinal basis for the epilepsies.

John Hughlings Jackson was singularly responsible for developing the modern concept of epilepsy. He moved the site of origin of epileptic seizures from the medulla to the cerebral cortex, included focal seizures as part of the epilepsy spectrum, and discarded the idea of epilepsy being due to a peripheral reflex mechanism. He regarded epileptic seizures as being due to a neuronal discharge. By the time of his Lumleian lectures to the Royal College of Physicians in 1890, Jackson’s concept of seizures, both epileptic and nonepileptic, was expressed according to his hierarchy of nervous system centers. The “highest level” centers with respect to the motor system were the prefrontal cortical regions, and “epilepsy proper” or “genuine epilepsy” was regarded as arising from that site. Jackson acknowledged that other nonmotor cortical regions were also highest level centers and could also be responsible for seizures. The “middle level” comprised the Rolandic regions, with or without the corpus striatum, and he regarded attacks from this region as “epileptiform.” These were characterized by the anatomic site of onset of the actual convulsion. The “lowest level” centers were only roughly and incompletely defined as the spinal cord, medulla, and pons with an indistinct upper boundary. These structures represented the lowest level of both the cerebral and the cerebellar systems. Seizures that could arise from the lowest level centers included anoxic convulsions and attacks associated with poisons such as curare, camphor, and absinthe. In this seminal paper,13 cerebellar fits were only briefly discussed and were regarded as separate from lowest level attacks. Jackson implied, however, that the discharges of “cerebellar seizures” would feed through the lowest level centers for their clinical expression.13,14

A number of the clinical reports of “cerebellar” seizures that were published in the late 19th and early 20th century were ascribed to a variety of pathologic causes other than cerebellar tumor, including rapid increase in intracranial pressure, hemorrhage, tumor or encephalitis of the brainstem, massive intraventricular hemorrhage, and sudden cerebral hypoxia.6,15-18

In 1940, Webster and Weinberger19 presented a paper detailing 158 cases of verified cerebellar tumors and their clinical manifestations. At that time, the general observations of the tonic nature of the Jacksonian cerebellar seizures were still held to be the case. In this paper, the authors documented that 13% of cerebellar tumor cases developed convulsions and, of these, 50% were tonic seizures with the remainder being clonic or focal in nature.

Decerebrate rigidity.

The concept of decerebrate rigidity developed at the turn of the century under the influence of Sherrington and the British School of Experimental Physiology.20 The relationship of decerebrate rigidity to Jacksonian cerebellar seizures was the subject of debate in the literature at that time and remains controversial today.

Early experimental animal studies demonstrated that decerebrate posturing arose when the lower postural mechanisms were “released” from cortical influence by experimental lesions of the brainstem at the level of the superior colliculus.20,21

Furthermore, electrical stimulation of the brainstem and cerebellum in animals was shown to produce stereotyped movements that were described as slow, sequential movements of postural muscles, as though the animals were moving from “one statuesque pose to another.”22-24 In these episodes, consciousness was usually preserved and there was no surface EEG changes to suggest an epileptiform basis to these events.25,26

Although well studied in animal preparations, relatively few human cases of decerebrate rigidity have been published. These cases do not report the brief “cerebellar” seizures of Jackson, but rather support sustained decerebrate posturing usually only evident in the terminal phase of the underlying illness.6,16,17,27-29 These episodes are typically described as tonic limb posturing with extension in the lower limbs and flexion and pronation of the upper limbs. Consciousness may be maintained during the attacks, however respiratory irregularity is common and may be fatal.6,16,18,19

Pathologic studies of cases with similar decerebrate posturing have also demonstrated supratentorial lesions interrupting corticobulbar pathways.18,30 Stereotypic tonic movements have likewise been reported immediately following brain death and are postulated to be generated by intact upper cervical spinal centers isolated from more rostral regions.31

The EEG correlates of decerebrate attacks have been reported in human cases and typically demonstrate flattening of the EEG rhythm during seizure episodes with low-voltage fast activity. Various authors16,17,32 have speculated that this phenomenon was due to stimulation of subcortical structures, such as the reticular activating system, rather than an epileptic manifestation arising from the cerebral cortex.

Cerebellar seizures and decerebrate attacks in contemporary practice.

Modern textbooks of neurology and epileptology as well as treatises on the cerebellum do not mention or give only brief attention to the fact that seizures can arise with cerebellar or posterior fossa lesions.33-35 It is sometimes suggested that cerebellar seizures represent attacks of transient decerebrate rigidity, although the classic descriptions suggest some differences in these entities in terms of posture and length of the attacks.2,16,17,32

The classic cerebellar seizures as described by Jackson appear to be rare in contemporary practice, at least in developed countries. We can only recall encountering one case in 20 years matching Jackson’s description—that of a young woman with an expanding pontine glioma who had prolonged bilateral tonic seizures with preservation of consciousness. It is probable that with better clinical diagnosis, the increasing rarity of tuberculous meningitis, advances in neuroimaging techniques, and appropriate early neurosurgical intervention that examples cited frequently in Jackson’s time and the early part of the 20th century are no longer a common part of clinical neurologic and neurosurgical practice. Jackson’s cerebellar seizures also differ from the recently described phenomena of concussive convulsions36 and seizures with epileptiform discharges resembling hemifacial spasm arising from neuronal cerebellar tumors and atrophic cerebellar lesions in children.37,38

Jackson’s clinical concept of cerebellar seizures has largely been over shadowed by the experimental physiologists who studied decerebrate rigidity. The mechanism of these two phenomena are probably related. Whether they are identical remains unclear; we are impressed by differences in the actual postures observed. What both points of view emphasize is that a variety of motor phenomena, including tonic posturing, can arise from posterior fossa lesions.