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Disease Entity

Acquired Supranuclear Ocular Motor Paresis

Disease

Acquired Supranuclear Ocular Motor Paresis (ASOMP) is a condition characterized by a bilateral, symmetric supranuclear ophthalmoplegia. There may be limitation of voluntary saccade but preserved smooth pursuit, vestibulo-ocular response (VOR), and slow phase optokinetic nystagmus¹. The ophthalmoplegia is often global and multidirectional but can be horizontal, vertical or both. Cardiovascular surgery is the most commonly documented risk factor for development of ASOMP^2,3,4. Associated symptoms of ASOMP may include other neurologic dysfunction (e.g., gait and/or speech ataxia⁵, weakness, dysphagia⁶, or emotional lability⁷).

Epidemiology

There are no published figures estimating the prevalence or incidence of ASOMP, but it is considered to be very rare.

Etiology

While the exact mechanism of ASOMP is not well understood, prolonged cardiopulmonary bypass time and hypothermia during cardiovascular surgery have been postulated as possible risk factors in the development of ASOMP². However, no structural correlate has been identified despite serial imaging studies in patients with ASOMP, although injury is postulated to the perineuronal network from occult microbleeds⁸ or microemboli.

Risk Factors

Cardiopulmonary bypass and deep, prolonged hypothermia associated with cardiovascular surgery are the most well-described and classical proposed risk factors for development of ASOMP. However, use of metrics like circulatory arrest or cardiopulmonary bypass times as predictors of development of ASOMP has been limited². Development of supranuclear ophthalmoplegia has also been documented after less invasive procedures like coronary artery angiography.⁹

Pathophysiology

It has been proposed that ASOMP may be due to injury of excitatory burst neurons (EBN) or omnipause neurons (OPN) ^1,10At rest, OPNs of the pontine reticular formation project to and inhibit EBNs¹⁰. While EBNs responsible for horizontal saccade are located in the caudal pons, EBNs controlling vertical and torsional saccade are located in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF)¹¹. Therefore, injury to EBNs or OPNs could produce a selective horizontal or vertical saccadic palsy seen in ASOMP. However, more recent work has shown histologically normal OPN and EBN in postmortem tissue of patients with ASOMP^12,13. Further, degeneration of perineuronal net (PNN) structures in vitro has also been proposed as a characteristically pathologic feature of ASOMP¹², though this hypothesis remains untested in vivo. Further, the mechanism of insult to these extracellular membrane structures remains poorly understood, though some have hypothesized that EBNs and OPNs may be especially susceptible to hypoxemic-ischemic insult because of their high firing rates and elevated metabolic demand¹³. Because the riMLF receives supply from the posterior thalamo-subthalamic paramedian artery (a branch of the posterior cerebral artery)¹⁴, embolization or microbleed of this vasculature after cardiac surgery might lead to ASOMP.

However, to date, no lesion that can fully explain the clinical features has been identified in serial imaging studies in ASOMP patients. However, the presumed localization has been the thalamo-mesocephalic junction because clinical findings of preserved motility with the vestibulo-ocular reflex (VOR) are suggestive of a supranuclear limitation.

Diagnosis

Signs & Symptoms

Patients with ASOMP classically present with a history of acute, bilateral, symmetric, painless, and global ophthalmoplegia immediately following or within days after cardiovascular surgery. Most characteristically, initiation of saccade is limited or abolished while smooth pursuit and slow phase optokinetic nystagmus may be preserved. Patients with ASOMP may also have gait ataxia, dysphagia or ataxic dysarthria, and delayed-onset seizure¹³.

Physical Examination

ASOMP classically presents on examination with little to no movement on attempted saccades, particularly with vertical gaze. However, pursuit and tracking using the vestibular-ocular reflex are often preserved. The finding of vertical saccadic palsy with preserved pursuit implies that the injury in ASOMP is located superior to the cranial nerve nuclei responsible for vertical gaze and motility. Thus, ASOMP is a so-called “supranuclear” gaze palsy. In contrast to the pathways used in generating saccades, smooth pursuit impairment has been linked instead to lesions of the basis pontis, with slight involvement of extrapontine structures¹⁵.

Because of its low incidence, ASOMP may be difficult to diagnose. Thus, awareness of ASOMP is an initial step to guide providers toward correct diagnosis and prompt care. Clinical features of differentially affected saccade with preserved pursuit, negative or nonspecific imaging study findings, and history of cardiovascular surgery form characteristic signs that should lead clinicians to suspect ASOMP.

Diagnostic Procedures & Laboratory Tests

Neuroimaging with magnetic resonance imaging (MRI) is used to exclude other structural causes of gaze paresis but typically the brain MRI in ASOMP are normal or show only nonspecific findings⁵. However, one fluoro-deoxy-glucose positron emission tomography (FDG-PET) study found diffuse and profound glucose hypometabolism¹⁶. Orbital ultrasound may also be useful in excluding muscular etiologies of gaze palsy. However, history and systematic testing of saccades form the cornerstone for diagnosis of ASOMP, and laboratory testing is usually not needed.

Differential Diagnosis

The differential diagnosis for ASOMP includes Parinaud/dorsal midbrain syndrome, Niemann-Pick Disease Type C, Progressive Supranuclear Palsy (PSP), and Cortico-Basal Syndrome (CBS). However, the acute onset of ASOMP with negative MRI in the setting of prior cardiac surgery is almost always sufficient to make the diagnosis. Clinically, the absence of convergence retraction nystagmus and light-near dissociation is helpful in differentiating ASOMP from Parinaud Syndrome. Bilateral lid retraction and a preference for downward gaze (“setting sun” sign) have also been documented in Parinaud Syndrome and not ASOMP. Neuroimaging with MRI classically shows a dorsal midbrain lesion in Parinaud Syndrome not present in ASOMP.

While the natural history of ASOMP is that of slow improvement after injury, PSP and CBS are characterized by progressive development. Niemann-Pick Disease may present with variable age and severity. Like ASOMP, Parinaud Syndrome can develop after an acute injury and thus a negative MRI is typically required to make the diagnosis of ASOMP.

Management

Primary Prevention

Because ASOMP is such a rare complication of cardiac surgery, there are no studies on prevention of ASOMP in the English literature. However, incidence of stroke after traditional repair of Stanford type A aortic dissection has been estimated to be as high as 20%, and this statistic has remained largely unchanged for the last 20 years.¹⁷ While it remains completely unstudied, if ASOMP is linked to microembolic etiologies, as with stroke, then the use of novel intravascular embolic protection devices (e.g. EmboShield) during cardiovascular surgery could theoretically reduce risk of ASOMP development.

Because ASOMP is classically acquired after cardiovascular surgery, preventative care for ASOMP should target vasculopathic risk factors like hypertension, hyperlipidemia, and atherosclerosis. Specifically, smoking cessation, diet counseling, and lifestyle interventions would decrease the incidence of disease requiring cardiac surgery and therefore the incidence of ASOMP.

Medical Therapy

The mainstay of care of ASOMP after cardiac surgery is rehabilitative therapy. Visual rehabilitation may include training the patient to use a head thrust to generate a doll’s head maneuver similar to the compensatory head thrusts of children with congenital ocular motor apraxia (COMA). This maneuver can be used to generate the vestibular ocular reflex to “drag” the eyes to a target, thus effectively achieving the same result as a saccade would. An example of the head thrust used in cases of COMA or ASOMP can be seen at the following link.

Rehabilitation of patients with ASOMP may also show marked improvement with proprioceptive input. Full pursuit of the patient’s own hand but not other pursuit targets has been documented in ASOMP.

With proper therapy, patients are noted to improve significantly over years of care. Notably, complete recovery of a patient with ASOMP has been described after therapy using vestibular stimulation with cold water injection into the external auditory canal¹⁸. While neither have been studied, magnetic or electrode stimulation could also be promising. Optimal management of ASOMP includes not only care for ocular motor complaints but also interdisciplinary management involving physio-, speech, or cognitive therapy for any other limitations from stroke associated with cardiovascular surgery.

Medical Follow Up

Though ASOMP is a defect that presents with oculomotor limitation, longitudinal follow-up with repeat visual field and OCT are helpful in tracking changes in vision, if any. However, the mainstay of care for patients with ASOMP should be consistent rehabilitative orthoptic exercise with vestibular stimulation.

Surgery

There is no surgical intervention for ASOMP.

Complications

In patients with ASOMP after cardiovascular surgery, progression and further complications are not common.

Prognosis

The natural history of ASOMP is slow improvement of the saccadic palsy. However, extent of improvement may be dependent on rehabilitation technique and frequency.

References

1. Yee RD, Purvin VA. ACQUIRED OCULAR MOTOR APRAXIA AFTER AORTIC SURGERY. Trans Am Ophthalmol Soc. 2007;105:152-159. 2. Devere TR, Lee AG, Hamill MB, Bhasin D, Orengo-Nania S, Coselli JS. Acquired supranuclear ocular motor paresis following cardiovascular surgery. J Neuro-Ophthalmol Off J North Am Neuro-Ophthalmol Soc. 1997;17(3):189-193. 3. Gardner TJ, Horneffer PJ, Manolio TA, et al. Stroke following coronary artery bypass grafting: a ten-year study. Ann Thorac Surg. 1985;40(6):574-581. doi:10.1016/s0003-4975(10)60352-9 4. Roach GW, Kanchuger M, Mangano CM, et al. Adverse cerebral outcomes after coronary bypass surgery. Multicenter Study of Perioperative Ischemia Research Group and the Ischemia Research and Education Foundation Investigators. N Engl J Med. 1996;335(25):1857-1863. doi:10.1056/NEJM199612193352501 5. Tisel SM, Ahlskog JE, Duffy JR, Matsumoto JY, Josephs KA. PSP-like syndrome after aortic surgery in adults (Mokri syndrome). Neurol Clin Pract. 2020;10(3):245-254. doi:10.1212/CPJ.0000000000000708 6. Sakiyama Y, Michizono K, Tomari S, Watanabe O, Nakahara K, Takashima H. [A case of a syndrome resembling PSP after aortic arch replacement under deep hypothermic circulatory arrest]. Rinsho Shinkeigaku. 2011;51(1):38-42. doi:10.5692/clinicalneurol.51.38 7. Solomon D, Ramat S, Tomsak R, et al. Saccadic palsy after cardiac surgery: Characteristics and pathogenesis. Ann Neurol. 2008;63:355-365. doi:10.1002/ana.21201 8. Jeon SB, Lee JW, Kim SJ, et al. New cerebral lesions on T2*-weighted gradient-echo imaging after cardiac valve surgery. Cerebrovasc Dis Basel Switz. 2010;30(2):194-199. doi:10.1159/000317108 9. Glisson C, Eggenberger E, Miller N. Supranuclear Ophthalmoplegia as a Complication of Coronary Angiography. Neuro-Ophthalmol. 2009;30:101-103. doi:10.1080/01658100600824669 10. Thurtell M, Tomsak R, Leigh R. Disorders of saccades. Curr Neurol Neurosci Rep. 2007;7:407-416. doi:10.1007/s11910-007-0063-x 11. Horn A. The reticular formation. Prog Brain Res. Published online 2006. doi:10.1016/S0079-6123(05)51005-7 12. Eggers SDZ, Horn AKE, Roeber S, et al. Saccadic Palsy following Cardiac Surgery: Possible Role of Perineuronal Nets. PloS One. 2015;10(7):e0132075. doi:10.1371/journal.pone.0132075 13. Eggers S, Horn A, Roeber S, et al. Saccadic palsy following cardiac surgery: A review and new hypothesis. Ann N Y Acad Sci. 2015;1343. doi:10.1111/nyas.12666 14. Percheron G. The anatomy of the arterial supply of the human thalamus and its use for the interpretation of the thalamic vascular pathology. Z Neurol. 1973;205(1):1-13. doi:10.1007/BF00315956 15. Malessa S, Gaymard B, Rivaud S, et al. Role of pontine nuclei damage in smooth pursuit impairment of progressive supranuclear palsy: a clinical-pathologic study. Neurology. 1994;44(4):716-721. doi:10.1212/wnl.44.4.716 16. Kim EJ, Choi KD, Kim J, et al. Saccadic Palsy after Cardiac Surgery: Serial Neuroimaging Findings during a 6-Year Follow-Up. J Clin Neurol Seoul Korea. 2014;10:367-370. doi:10.3988/jcn.2014.10.4.367 17. Ghoreishi M, Holmes SD, Taylor BS. Stroke after type A aortic dissection repair: Can we do better? J Thorac Cardiovasc Surg. 2020;159(4):e257. doi:10.1016/j.jtcvs.2019.07.059 18. Marshall CR, Maynard FM. Vestibular stimulation for supranuclear gaze palsy: case report. Arch Phys Med Rehabil. 1983;64(3):134-136.