Kinematic and Diffusion Tensor Imaging Definition of Familial Marcus Gunn Jaw-Winking Synkinesis

Antonella Conte,Patrizio Bollero,Nicola Toschi,Francesco Garaci,Alfredo Berardelli,Roberto Floris,Bruno Dallapiccola,Marika Falla,Giovanni Fabbrini,Francesco Brancati,Matteo Bologna,Celia Oreja-Guevara

doi:10.1371/journal.pone.0051749

Abstract

BackgroundMarcus Gunn jaw-winking synkinesis (MGJWS) is characterized by eyelid ptosis, which disappears during jaw movement. Familial MGJWS is an extremely rare condition. Some authors suggested that MGJWS is due to neural misdirection in the brainstem whereas others suggested that aberrant reinnervation or ephapse may be responsible for synkinetic activity. Pathogenesis of this condition is therefore still unclear.Methodology/Principal FindingsTo investigate pathogenetic mechanism in familial MGJWS we performed neurophysiological (EMG, Blink Reflex, Recovery cycle of the R2 component of the blink reflex, Masseter inhibitory reflex, BAEPS and kinematic analysis) and neuroradiological (MRI, Diffusion Tensor Imaging) investigations in a member of a multigenerational family with autosomal dominant Marcus Gunn jaw-winking synkinesis (MGJWS). Kinematic analysis of eyelid and jaw movements disclosed a similar onset and offset of the eyelid and jaw in both the opening and closing phases. The excitability of brainstem circuits, as assessed by the blink reflex recovery cycle and recovery index, was normal. Diffusion Tensor Imaging revealed reduced fractional anisotropy within the midbrain tegmentum.Conclusions/SignificanceKinematic and MRI findings point to a brainstem structural abnormality in our familial MGJWS patient thus supporting the hypothesis of a neural misdirection of trigeminal motor axons to the elevator palpebralis muscle.

Highlights

Marcus Gunn jaw-winking synkinesis (MGJWS) is characterized by eyelid ptosis, which disappears during jaw movement
The kinematic analysis performed in this patient showed that the MGJWS was characterized by a similar onset and offset of the eyelid and jaw movements in both the opening and closing phases
Eyelid activation involves three neural pathways: the elevator palpebralis muscle, which is innervated by the oculomotor nerve, raises the upper eyelid; gentle upper eyelid closure depends on the inhibition of motor axons directed to the elevator palpebralis muscle, which occurs in the brainstem at the level of trigeminal motor nucleus; forced eyelid closure depends on the orbicularis oculi muscle, which is innervated by the facial nerve

Summary

Introduction

Marcus Gunn jaw-winking synkinesis (MGJWS) is characterized by eyelid ptosis, which disappears during jaw movement. Neurophysiological studies have suggested that the MarcusGunn phenomenon may be due to a congenital neural misdirection of trigeminal motor axons of the external pterygoid muscle (responsible for jaw depression and protraction) to the elevator palpebralis muscle [3]. Other authors have instead suggested that the Marcus-Gunn phenomenon may originate from aberrant reinnervation at the brainstem level rather than at the peripheral level [4]. Some authors suggested that MGJWS is due to neural misdirection in the brainstem whereas others suggested that aberrant reinnervation or ephapse may be responsible for synkinetic activity. Pathogenesis of this condition is still unclear

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Conclusion