Overlapping Phenomenology in Focal Motor Epilepsy and Movement Disorders

The overlapping phenomenology between focal motor epilepsy and other movement disorders suggests that current diagnostic criteria should improve classifications of motor manifestations, according to study results published in Parkinsonism & Related Disorders.

The investigators of this study sought to determine the extent to which focal motor seizures can present with a phenomenology that resembles various movement disorders.

The study cohort included 100 consecutive patients with confirmed focal motor seizures using video electroencephalography (EEG). Participants underwent video EEG monitoring during the pre-ictal, ictal, and post-ictal periods at the epilepsy unit in the department of human neurosciences of Sapienza University, Rome. Three groups of investigators (movement disorder experts, epileptologists, and general neurologists) rated body sites and movement disorders using standardized data sheets. Movement disorders, including tremor, dystonia, and stereotypies, were diagnosed according to recently published criteria or expert-derived definitions.

All 3 groups of investigators determined similar numbers of focal motor episodes, but the inter-rater agreement on involved body sites and movement disorder classification was generally poor within each group. Agreement on upper limb diagnosis among motor disorder experts was moderate, as was that on lower limb diagnosis among general neurologists. Because of insufficient inter-rater agreement, the investigators conservatively identified 29% of the sample (n=29) with focal motor seizures that phenomenologically presented as recognizable movement disorders. Of the 29 episodes, 10 (34.5%) were characterized as myoclonus, 9 (31%) as dystonia, 4 (13.8%) as dyskinesias, 3 (10.3%) as sterotypies, 2 (6.9%) as myoclonus-dystonia, and 1 (3.4%) as tremor. Symptoms were generally unilateral and most commonly involved the upper limb (17 episodes), face (9 episodes), neck (4 episodes), or lower limb (4 episodes).

Limitations to the study included the low inter-rater agreement, which resulted in a more conservative analysis, and the lack of other electrophysical assessments. Video EEG tests have a limited resolution that may not allow investigators to identify epileptogenic zones or involvement of subcortical structures.  

Reported overlap of movement phenomenology between focal motor epilepsy and other movement disorders suggests that a judicious approach to diagnosis is required, especially because the therapeutic implications differ considerably. Poor agreement among the investigators further indicates a need for revision of current definitions and diagnostic criteria for classifying movement disorders.

Reference                    

Fasano A, Di Bonaventura C, Bove F, et al. Movement disorders phenomenology in focal motor seizures [published online October 16, 2018]. Parkinsonism Relat Disord. doi:10.1016/j.parkreldis.2018.10.021