Objective: To examine the extent to which focal motor seizures can present with a phenomenology fulfilling diagnostic criteria for one or more movement disorder.

Background: The epileptic seizure definition implies pathophysiology rather than phenomenology. On the other hand, the diagnosis and classification of a movement disorder relies on phenomenology. Therefore, theoretically, a motor seizure can phenomenologically resemble one or more movement disorder.

Methods: A series of 100 consecutive patients with focal motor seizures who had detailed clinical history and video-EEG were rated by movement disorders experts (MDE), epileptologists (EPI), and general neurologists (GEN). We also examined whether seizure’s presentation with a movement disorder might be associated to a specific EEG correlate. The three groups of physicians included five MDE (age: 46.0±8.0 years, MD for 21.8±8.2 years and involved in the care of movement disorders patients for 14.8±8.7 years), four EPI (44.0±5.7 years, MD for 19.5±5.2 years, caring for epilepsy patients for 11.0±4.1 years) and 4 recently board certificated neurologists (NEU, 35.8±1.7 years, MD for 12.0±1.4).

Results: No difference in the number of focal motor seizures per video was found among the three groups: 1.4±0.6, 1.2±0.6 and 1.3±0.5 in MDE, EPI and GEN, respectively (p>0.15). Due to insufficient inter-rater agreement, we restricted further analyses on episodes where MDE reached full agreement on a given diagnosis (κ of 1). These episodes involved 29 patients (29%) and were characterized as: myoclonus (10), dystonia (9), dyskinesias (4), stereotypies (3), myoclonus-dystonia (2), and tremor (1). Upper limb was most commonly involved (17 episodes) followed by face (9), neck and lower limb (4 each), shoulder (2), and trunk (1). Symptoms were unilateral in all episodes except seven (3 ‘blepharospasm’, 2 lower limbs dyskinesias, 1 oromandibular dystonia and 1 upper limbs stereotypies). In five of the patients with bilateral symptoms there was EEG evidence of bi-hemispheric epileptic activity, which was also found in three more episodes with unilateral phenomenology. Comparing the EEG localization of the two most common movement disorders (myoclonus and dystonia), was found no significant association between location and phenotype.

Conclusions: Movement disorders and epilepsy may share both phenomenology and pathophysiological bases. Our study systematically explored these overlaps, which can challenge the differential diagnosis of these conditions.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/movement-disorders-phenomenology-in-focal-motor-seizures/