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Atonic phenomena and partial seizures. A reappraisal
1Oregon Comprehensive Epilepsy Program, Good Samaritan Hospital & Medical Center, Portland 97210, USA.
Advances in Neurology
|January 1, 1995
Summary
Partial seizures can involve three distinct phenomena: focal atonic seizures, epileptic negative myoclonus, and drop attacks. These events, characterized by motor impairment, may stem from varied neurological mechanisms.
Area of Science:
- Neurology
- Epileptology
- Clinical Neurophysiology
Background:
- Partial seizures can manifest with diverse ictal phenomena beyond typical convulsions.
- Focal atonic seizures, epileptic negative myoclonus, and drop attacks represent distinct ictal events observed in partial epilepsy.
- Accurate diagnosis of these phenomena often requires advanced monitoring techniques like simultaneous electroencephalography (EEG) with video and polygraphy.
Purpose of the Study:
- To delineate three specific ictal phenomena occurring in partial seizures: focal atonic seizures, epileptic negative myoclonus, and drop attacks.
- To explore the potential underlying pathophysiological mechanisms for each of these distinct seizure manifestations.
- To highlight diagnostic challenges and the importance of multimodal monitoring in identifying these subtle seizure types.
Main Methods:
- Review of clinical presentations and diagnostic criteria for focal atonic seizures, epileptic negative myoclonus, and drop attacks in partial epilepsy.
- Analysis of proposed pathophysiological mechanisms based on seizure semiology and neurophysiological principles.
- Emphasis on the role of simultaneous electroencephalography (EEG), video monitoring, and polygraphy in diagnosis.
Main Results:
- Focal atonic seizures are characterized by ictal paresis/paralysis independent of or preceding convulsive activity.
- Epileptic negative myoclonus involves brief muscle atonia affecting motor coordination and postural control.
- Drop attacks in partial seizures, particularly from temporal or frontal lobe epilepsy, may share mechanisms with generalized seizure-induced drop attacks.
Conclusions:
- Focal atonic seizures likely arise from localized cortical dysfunction impacting motor execution.
- Epileptic negative myoclonus may be linked to transient local inhibition within the motor cortex.
- Drop attacks in partial seizures could involve brainstem inhibitory pathways, similar to generalized seizure mechanisms.