Trigeminal-Abducens Pseudosynkinesis: Distinguishing Unconscious Motor Habits From True Synkinesis

Clinical Correspondence Section Editors: Robert Avery, DO Karl C. Golnik, MD Caroline Froment, MD, PhD An-Gour Wang, MD Trigeminal-Abducens Pseudosynkinesis: Distinguishing Unconscious Motor Habits From True Synkinesis Pierre R. Bourque, MD, David A. Grimes, MD, Daniel A. Lelli, MD S ynkinesis describes obligatory linked movements that depart from the expected physiologic patterns of voluntary motor activation. A wide variety of cranial and appendicular synkineses have been described in acquired and congenital disorders of both the central and peripheral nervous systems. These phenomena must be distinguished from atypical habitual voluntary or unconscious movement patterns. We present here a case where habitual ipsilateral jaw and horizontal gaze deviation appeared to be consistent with a trigeminal-abducens synkinesis. We demonstrate how a careful clinical and electromyographic analysis may be required to accurately characterize the movement disorder. We propose the term “pseudosynkinesis” to describe such suppressible linked movements. A 70-year-old man assessed for mild dysphasia was incidentally noted to have striking jaw deviation during the assessment of horizontal gaze. There appeared to be a consistent wide amplitude ipsilateral jaw deviation linked to both target-directed horizontal ocular pursuit and voluntary ocular saccades (see Supplemental Digital Content, Video E1, http://links.lww.com/WNO/A435). The neuroophthalmologic examination and the specific assessment of the trigeminal nerves were completely normal. It was noted that that ipsilateral mandibular and ocular deviation were not always perfectly synchronous. When asked to actively avoid linked movements, the patient could partially or at times completely suppress jaw deviation. He could be instructed to successfully achieve a contralateral jaw deviation during ipsilateral horizontal gaze. In addition, no clinically detectable ipsilateral jaw movement was triggered by reflex ocular movements, such as the fast phase of optokinetic nystagmus or the ocular component of the visually enhanced vestibular ocular reflex. An EMG monopolar needle was inserted deeply into Division of Neurology (PRB, DAG, DL), Department of Medicine, The Ottawa Hospital, Ottawa, Canada; and The Ottawa Hospital Research Institute (PRB, DAG, DAL), Ottawa, Canada. The authors report no conflicts of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www. jneuro-ophthalmology.com). P. R. Bourque and D. A. Grimes are equal first authors. Address correspondence to Pierre R. Bourque, MD, Division of Neurology, Department of Medicine, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, ON K1Y-4E9, Canada; E-mail: pbourque@ toh.ca Bourque et al: J Neuro-Ophthalmol 2021; 41: e337-e338 the lateral pterygoid muscle, through an external approach at the level of the temporomandibular joint. Needle placement was verified by demonstrating bursts of motor unit potentials that were synchronous with every contralateral jaw deviation. Needle EMG did not reveal any subclinical activation of the lateral pterygoid muscle when the patient was asked to voluntarily suppress jaw movement during lateral gaze, nor when reflex ocular movements were tested. The patient stated that he had not been aware he produced such lateral jaw deviations. He later postulated he may have developed this unconscious habit as an attempt to improve his range of lateral gaze while playing competitive sports. A true synkinesis is presumed to reflect an aberrant supranuclear or lower motor neuron pathway that has become obligatory, or “hard-wired.” For example, 35% of cases of congenital mirror movement disorder have been associated with mutations of RAD 51 or deleted in colorectal cancer (DCC) genes. DCC encodes a transmembrane receptor for netrin-1, a protein that helps guide axons across the midline in the developing nervous system (1). In cases of facial synkinesis following lesions of the facial nerve, peripheral a motor axons have adopted atypical trajectories during axonal regrowth. The same mechanism applies to parasympathetic axons to explain crocodile tears or gustatory sweating. Several synkineses involving ocular nerves have been described. Some of the congenital forms have been grouped as congenital cranial dysinnervation disorders (2). In Duane retraction syndrome, there is fibrosis of the lateral rectus from congenital defective abducens nerve innervation, coupled with aberrant patterns at the level of supranuclear ocular pathways or oculomotor nerve branches. In patients with Marcus-Gunn phenomenon, there is a rapid synkinetic activation of upper lid elevation with a wide variety of jaw movements such as chewing, jaw opening, sucking, or swallowing. Congenital trigeminal-abducens synkinesis may present as obligatory jaw deviation triggered by lateral gaze or the reverse pattern of involuntary lateral gaze during chewing or sucking movement. In congenital cases this synkinesis is bilateral and may be noted as early as the neonatal period (3). Unilateral acquired trigeminal-abducens synkinesis has been described following trauma near the apex of the petrous temporal bone, where both nerves are in close proximity (4). Our case exemplifies the pitfalls in determining whether linked movement patterns are obligatory and “hard wired” or e337 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence whether they could represent an involuntary unconscious habit movement or even a conversion disorder. A systematic analysis for true synkinesis should not only demonstrate lack of voluntary suppression, but also establish that the movements are almost invariably linked and synchronous. Different strategies may be required to recruit the triggering movement of the synkinesis, with both volitional and reflexive movements. Electromyography may also be useful in establishing whether there is more subtle subclinical muscular activation (5). We conclude that our patient had a suppressible pseudosynkinesis of voluntary gaze and jaw deviation. The patient provided written informed consent for the publication of the video. e338 REFERENCES 1. Srour M, Riviere JB, Pham JM, Dube MP, Girard S, Morin S, Dion PA, Asselin G, Rochefort D, Hince P, Diab S, Sharafaddinzadeh N, Chouinard S, Theoret H, Charron F, Rouleau GA. Mutations in DCC cause congenital mirror movements. Science. 2010;328:592. 2. Bosley TM, Abu-Amero KK, Oystreck DT. Congenital cranial dysinnervation disorders: a concept in evolution. Curr Opin Ophthalmol. 2013;24:398–406. 3. Ghodasra DH, Nallasamy S, Binenbaum G. Congenital trigeminoabducens synkinesis in a neonate. J AAPOS. 2009;13:417– 418. 4. McGovern ST, Crompton JL, Ingham PN. Trigemino-abducens synkinesis: an unusual case of aberrant regeneration. Aust N Z J Ophthalmol. 1986;14:275–279. 5. Rubin DI. Normal and abnormal spontaneous activity. Handb Clin Neurol. 2019;160:257–279. Bourque et al: J Neuro-Ophthalmol 2021; 41: e337-e338 Copyright © North American Neuro-Ophthalmology Society. 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