03 October 2024: Articles
Rare Case of Post-Traumatic Abducens-Oculomotor Nerve Synkinesis Exhibiting Unusual Ocular Motility
Unusual clinical course
Ahmad M. Alaraj 1ABCDEFGDOI: 10.12659/AJCR.944565
Am J Case Rep 2024; 25:e944565
Abstract
BACKGROUND: Acquired synkinesis is a well-known phenomenon following oculomotor nerve injury. The abnormal movement appears within the distribution of 1 nerve, or other cranial nerves may be involved. The common misdirection of aberrant regeneration of oculomotor nerve involves the lid, extraocular muscles, or pupil. This report presents a case of aberrant connection between abducens and oculomotor nerve, which is quite rare.
CASE REPORT: A 21-year-old man with history of left-sided frontal, lateral orbital wall, and zygomatic fracture from head trauma in a motor vehicle accident presented for evaluation. He was comatose for 6 weeks in the intensive care unit. Six months later, he presented to the ophthalmology clinic for an eye examination. He had no history of eye problems prior to this accident. His best corrected visual acuity in the right eye was 20/20 and the left eye had no light perception. The right eye exam was normal, with normal ocular motility. The left eye exam showed small esotropia in primary position with markedly decreased adduction, elevation, and minimal depression, but on attempted abduction, the left eye would adduct instead. There was no globe retraction when left eye abduction was attempted. The abnormal movement seen resulted from third nerve function during sixth nerve stimulation, due to unusual ocular motility with abnormal connection between the sixth and third cranial nerves.
CONCLUSIONS: The most likely pathophysiologic mechanism here is peripheral neuronal misdirection hypothesis after trauma. Careful and detailed examination of a patient presenting with unusual ocular motility after trauma is very important. The abnormal connection between the sixth and third cranial nerves is quite rare but can occur.
Keywords: Abducens Nerve Injury, Nerve Regeneration, Ocular Motility Disorders, Oculomotor Nerve Injuries
Introduction
Acquired synkinesis can occur after trauma and has frequently been described after oculomotor nerve injury. The abnormal movement appear within the distribution of one nerve or other cranial nerves may be involved. Abducens-oculomotor synkinesis is quite unusual. The present report is of case of unusual ocular motility due to abnormal connection between the sixth and third cranial nerves following severe head and orbit trauma. Very few similar cases have been published.
Case Report
A 21-year-old man, previously healthy with no history of preexisting ocular motility disorders, sustained severe left-sided head trauma in a motor vehicle accident (MVA). He was comatose for 6 weeks in the intensive care unit (ICU). He had left-sided frontal, lateral orbital wall, and zygomatic fractures with hemorrhagic contusion in the left frontal lobe. During his stay in the ICU, the family observed that the patient’s left eye movements were incomplete. An examination of the left eye in the ICU revealed a pale optic disc. He was scheduled to visit the ophthalmology clinic upon his discharge. On examination 6 months later, the best corrected visual acuity was 20\20 right eye and NLP left eye. His left pupil diameter was 6 mm and not reactive, and a left afferent pupillary defect was present. An ocular motility exam showed a small esotropia in the primary position. On duction testing, the left eye had markedly decreased adduction, elevation, and minimal depression, but on attempted abduction, the eye would adduct (Figure 1). Forced duction testing was negative, indicating that left oculomotor nerve function was subnormal. Right eye motility was full. The rest of his examination was normal apart from left optic atrophy (Figure 2). Brain MRI revealed no brain stem lesions. The patient provided informed consent for the publication of his case and accompanying photographs. The details of the patient’s file are available to interested researchers and clinicians upon request. The patient’s condition remained unchanged for 1 year.
Discussion
Various patterns of synkinesis have been observed following both congenital and acquired third nerve palsies [1–3]. The hypotheses that have been proposed to explain oculomotor synkinesis include misdirection of regenerating axons, ephatic transmission, central reorganization, and denervation supersensitivity [1,2,4].
Aberrant regeneration is a recognized neurophysiological phenomenon following peripheral third nerve palsy. It commonly occurs when the palsy is secondary to trauma, aneurysm, or tumor, and the nerve does not recover for several months [1].
Acquired abducens-oculomotor synkinesis is quite unusual, with few reported cases [1,4–6]. The paradoxic eye movement in the current case can be described by neuronal misdirection theories. Following trauma to the orbit, the oculomotor and abducens nerve functions were disrupted, with abnormal function, causing medial rectus muscle contracture when the lateral rectus muscle is stimulated. The theory behind this mechanism proposes that the regeneration of injured peripheral neurons leads to a bridging matrix of proliferating cells with sprouts of regenerated axons that innervate tissues inappropriately [2,4]. Experimental studies by Cajal and Whitman showed that during repair processes, newly formed axons can randomly grow into the wrong muscle or distal stump [4,7]. In contrast to Duane’s retraction syndrome [8], we could not see any globe retraction when the left eye attempted abduction, in addition to lack of ocular motility disorders, as evident by the history and normal results of a previous childhood examination.
Conclusions
The most likely pathophysiologic mechanism explaining the present case is the peripheral neuronal misdirection hypothesis after trauma. Careful and detailed examination of a patient presenting with unusual ocular motility after trauma is very important. The abnormal connection between the sixth and third cranial nerves is quite rare, but has been reported.
Figures
Figure 1.. Ocular motility evaluation showed small esotropia in primary position, with normal version testing of right eye in all gazes. The left eye showed abnormal movement when the patient asked to look to the left side; the left eye adducted. The left eye had markedly decreased adduction and elevation and minimal depression. Figure 2.. Left optic disc pallor.References:
1.. Packer AJ, Bienfang DC, Aberrant regeneration involving the oculomotor and abducens nerves: Ophthalmologica, 1984; 189; 80-85
2.. Sibony PA, Lessell S, Gittinger JW, Acquired oculomotor synkinesis: Surv Ophthalmol, 1984; 28; 382-90
3.. Walsh FB, Third nerve regeneration: A clinical evaluation: Br J Ophthalmol, 1957; 41; 577-98
4.. Buckley EG, Ellis FD, Postel E, Saunders T, Posttraumatic abducens to oculomotor nerve misdirection: J AAPOS, 2005; 9(1); 12-16
5.. Jordan DR, Miller DG, Anderson RL, Acquired oculomotor-abducens synkinesis: Can J Ophthalmol, 1990; 25; 148-51
6.. Wutthiphan S, Foster SR, Poonyathalang A, Pongpech S, Abducens-oculomotor synkinesis associated with internuclear ophthalmoplegia and acquired abducens nerve palsy: J Pediatr Ophthalmol Strabismus, 2006; 43(4); 246-49
7.. Whitman MC, Axonal growth abnormalities underlying ocular cranial nerve disorders: Annu Rev Vis Sci, 2021; 7(1); 827-50
8.. Waters M, Acquired synergistic divergence: contrary to current literature: Br Ir Orthopt J, 2020; 16(1); 25-28
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