Faciobrachial Dystonic Seizures: The Borderland Between Epilepsy and Movement Disorders

Faciobrachial dystonic seizures (FBDS) are a pathognomonic manifestation of anti-leucine-rich glioma-inactivated 1 (LGI1) encephalitis, whose nature (epileptic seizures vs. paroxysmal movement disorders) and origin (cortical vs. subcortical) have been long debated. Typical FBDS are sudden, brief, lateralized tonic contractions (or “spasms”) mainly involving the upper limb and the ipsilateral face (or, less frequently, the leg), often associated with hand dystonia. They can be unilateral, bilateral asynchronous, or alternating with a short delay (so called à bascule) and tend to recur several times day. Although patients are usually responsive during FBDS, a concomitant impairment of awareness can be supposed at times. In some cases, movements are so violent and jerky, and the involvement of trunk and lower limbs so remarkable to cause traumatic falls, which often leads physicians to suspect and investigate different diseases (especially cardiac arrhythmias and drop attacks). The phenomenology of FBDS is so peculiar as to be easily recognizable. Nevertheless, sometimes it might be misinterpreted or even overlooked: indeed, FBDS can be observed not only as isolated events but also within much more complex paroxysmal phenomena, set in a variable sequence of other motor and nonmotor signs (Video S1). It has been documented that they can even precede or follow full-blown temporal lobe seizures. The nosographic and pathophysiological definition of FBDS is an area of active debate. On one hand, some clinical features, such as extremely short duration, bilateral alternating pattern, face involvement, and poor response to antiseizure medications, as well as specific functional neuroimaging findings, that is, basal ganglia hypermetabolism documented by positron emission tomography (Supplementary Figure S1), support the hypothesis of FBDS being paroxysmal movement disorders. On the other hand, their epileptic nature has been suggested not only by their stereotyped appearance and the possible concomitant impairment of awareness, but also by emerging neurophysiological evidence. Indeed, cortical myoclonic jerks superimposed to tonic spasms have been recorded during FBDS thanks to jerk-locked backaveraging techniques. Moreover, an infraslow activity preceding FBDS by less than 1 second, maximal over the contralateral mid frontal regions, has been consistently documented through accurate electroencephalogram analysis, further supporting the cortical origin of these motor spasms. The coexistence of isolated FBDS, clear-cut epileptic seizures, and peculiar “mixed” paroxysmal phenomena in some patients with anti-LGI1 encephalitis, along with the aforementioned neurophysiological and neuroimaging findings, suggests the impairment of a wide cortico-subcortical network involving the basal ganglia and frontal and temporal cortices. Therefore, it might be hypothesized that the variable site and extent of entrainment of this dysfunctional network could be responsible for the complex nature and semiology of these fascinating manifestations. The ongoing research on the elusive pathophysiological mechanisms underlying FBDS might contribute to overcome (or question, at least) the long-standing dichotomy between the cortical and subcortical origins of involuntary paroxysmal motor phenomena in accordance with the novel network-focused perspective on neurological diseases.