Selective saccadic palsy

Head-free gaze shifts; Slow/absent saccades; Normal smooth pursuit; Absent optokinetic quick phases of nystagmus; Normal oculocephalics; Absent torsional quick phases of nystagmusDifficulty redirecting gazeThis case is published courtesy of Scott D.Z. Eggers, M.D., Department of Neurology, Mayo Clinic College of Medicine (1). The patient is a healthy 50 year old woman who underwent otherwise uncomplicated aortic valve replacement for an incidentally discovered ascending aortic aneurysm. Upon awakening from anesthesia she noted difficulties directing her gaze and began using head movements to facilitate gaze shifts. She had no dysarthria, dysphagia or gait instability. She was discharged and had no problems other than her visual complaints for three months at which time she developed complex partial seizures that responded to levetiracetam. On examination ten months post-operatively, a general neurological exam was notable only for diffuse hyporeflexia. Visual acuity, pupils, visual fields and fundoscopic examination were normal. Examination of the eye movements showed: 1. Straight ahead fixation was steady and no spontaneous saccades, square wave jerks or nystagmus was seen ophthalmoscopically. 2. She made no fast volutional or reflexive saccades in any direction, but instead made extremely slow eye movements to eventually reach a target, except for slightly faster downward saccades. 3. Pursuit was smooth and of full range horizontally and vertically, even with high frequencies. 4. With a horizontal optokinetic drum the eyes can fix laterally in the orbits without any corrective quick phases, but she made a few downbeats of nystagmus with upward optokinetic (OKN) drum. 5. Vestibular slow phases, with slow oculocephalics and with rapid head impulse testing were normal. 6. Torsional head rolling produced excellent counter-rolling, but without any torsional quick phases. 7. Fixation suppression of the vestibule-ocular reflex was intact. 8. With head-free gaze shifts, she made exaggerated head turns associated with blinks, with contraversive vestibular slow phase eye movements that place the eyes in the corner of the orbits until the head was maximally rotated, and then the eyes would continue to slowly drift toward the target as can be seen in congenital ocular motor apraxia. Eye movements were recorded with video oculography. Figure A shows video oculography recordings of the patient. Horizontal saccades were absent during random saccade paradigm (top) but sinusoidal smooth pursuit was normal across all frequencies (bottom). Vertical eye movements demonstrated the same findings. Additionally rotary chair sinusoidal vestibular and optokinetic testing demonstrated normal vestibular slow phases and optokinetic ocular following reflex, but absent vestibular or OKN quick phases of nystagmus (not shown). Investigations: Figure B MRI of the brain showing a focus of increased FLAIR signal (an increased T2 signal, not shown) in the right dorsomedial pons (arrow) ten months after surgery. Comment: Two additional cases have been reported by Eggers et al (1). Patient #2 a 53 year old man and patient #3 a 57 year old man who underwent aortic valve-aneurysm and aortic dissection repair and upon awakening both had lost all saccadic eye movements including optokinetic and vestibular quick phases of nystagmus. As with the 50 year old woman (described above) all other eye movement classes were preserved. Both men had gait ataxia and the 53 year old man also had dysarthria and limb dysmetria. Patient #3, the 57 year old man developed complex partial seizures. The MRI in Patient #2 showed left mesial temporal sclerosis and hippocampal atrophy. The MRI in Patient #3 showed patchy subcortical white matter small vessel changes. The patients were examined 6 to 22 months after surgery with no improvement in the eye movement findings. They all remain unable to read or drive.The eye movements in this patient with selective saccadic palsy show: With head free gaze shifts, exaggerated head turns associated with blinks and controversive vestibular slow phase eye movements that place the eyes in the corner of the orbits until the head is maximally rotated. Then the eyes continue to slowly drift towards the target as can be seen in congenital ocular motor apraxia. With head fixed, the eyes make small slow hypometric saccades. Intact smooth pursuit eye movements both horizontally and vertically. With horizontal OKN, the eyes pursue the lines and fix laterally in the orbits without any corrective quick phases. Torsional head rolling produced excellent counter-rolling, but without any torsional quick phases.MRI showed a focus of increased FLAIR signal in the right dorsomedial pons.The functional classes of eye movements (saccades, pursuit, vestibular, optokinetic, vergence) have different anatomic substrates. Premotor (excitatory) burst neurons (PBN) reside in the pons for horizontal saccades and the midbrain for vertical saccades. Omnipause neurons (OPN) in the paramedian pontine raphe interpositus (RIP) transiently cease inhibiting the PBN to allow saccade initiation. Long lead burst neurons (LLBN) in the brainstem receive and combine various cortical and collicular saccade commands and project to PBN and the cerebellum, potentially directing target identification and providing a trigger signal for saccade initiation. Whether a single lesion could cause selective slowing of all saccades but spare other eye movements has been unclear. Perhaps counterintuitively, tiny neurotoxic lesions in the RIP have produced slowing of horizontal and vertical saccades (2), and clinical lesions of the paramedian pons, presumably affecting the OPN, have also caused similar horizontal and vertical saccade slowing in post-cardiac surgery cases. (3, 4). An elegant brainstem neural network model of saccade generation has recently been proposed, explaining how OPN lesions could slow saccades by eliminating the normal post-inhibitory rebound in premotor burst neurons (via membrane channel properties(5), leaving the remaining trigger signal from LLBN insufficient to generate a normal velocity saccade (6). Additional findings, ataxia, seizures, PSP-like syndrome in some of our and others' cases suggests more widespread injury (7-9). Sub-MRI-threshold bihemispheric frontoparietal eye field lesions seem unlikely to explain selective saccadic palsy given the preserved pursuit and impaired reflexive saccades and quick phases.The mechanism of injury remains unclear, but an ischemic cause seems likely given the immediacy after surgery and the ischemic-appearing pontine lesion in our patient 1 and in the single autopsy case (3). While embolic phenomena are possible, susceptibility of specific vulnerable neuronal populations to hypoxic/ischemic injury in the setting of cardiopulmonary bypass and hypothermic circulatory arrest is another potential mechanism (8). These cases occurred despite the fact that the surgeries were otherwise uncomplicated, with normal circulatory arrest and total operative time and without hypotension.Brainstem hypoxic/ischemic injury Hypotension or possibly intraoperative hypothermia may contribute to the development of this syndrome.None available. Patients remain visually disabled. View Selective Saccadic Palsy (data Solomon D et al (7) to see figures and tables.1. Eggers SD, Moster ML, Cranmer K. Selective saccadic palsy following cardiac surgery. Neurology 2008;70:318-320. http://www.ncbi.nlm.nih.gov/pubmed/18057315 2. Kaneko CR. Effect of ibotenic acid lesions of the omnipause neurons on saccadic eye movements in rhesus macaques. J Neurophysiol 1996;75(6):2229-2242. http://www.ncbi.nlm.nih.gov/pubmed/8793737 3. Hanson MR, Hamid MA, Tomsak RL, Chou SS, Leigh RJ. Selective saccadic palsy caused by pontine lesions: clinical, physiological, and pathological correlations. Ann Neurol 1986;20(2):209-217. http://www.ncbi.nlm.nih.gov/pubmed/3752965 4. Tomsak RL, Volpe BT, Stahl JS, Leigh RJ. Saccadic palsy after cardiac surgery: visual disability and rehabilitation. Ann N Y Acad Sci 2002;956:430-433. http://www.ncbi.nlm.nih.gov/pubmed/11960832 5. Miura K, Optican LM. Membrane channel properties of premotor excitatory burst neurons may underlie saccade slowing after lesions of omnipause neurons. J Comput Neurosci 2006;20(1):25-41. http://www.ncbi.nlm.nih.gov/pubmed/16511656 6. Ramat S, Leigh RJ, Zee DS, Optican LM. What clinical disorders tell us about the neural control of saccadic eye movements. Brain 2007;130(Pt 1):10-35. http://www.ncbi.nlm.nih.gov/pubmed/17121745 7. Solomon, D, Ramat S, Tomsak RL, Reich SG, Shin RK. Zee DS, Leigh RJ. Saccadic Palsy following Cardiac Surgery: Characteristics and Pathogenesis. Ann of Neurol 2007;62:1-11. http://www.ncbi.nlm.nih.gov/pubmed/17696176 8. Mokri B, Ahlskog JE, Fulgham JR, Matsumoto JY. Syndrome resembling PSP after surgical repair of ascending aorta dissection or aneurysm. Neurology 2004;62(6):971-973. http://www.ncbi.nlm.nih.gov/pubmed/15037703 9. Bernat JL, Lukovits TG. Syndrome resembling PSP after surgical repair of ascending aorta dissection or aneurysm. Neurology 2004;63(6):1141-1142; author reply 1141-1142. http://www.ncbi.nlm.nih.gov/pubmed/1545232