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Show Pursuit-Paretic and Epileptic Nystagmus in MELAS Seo Young Choi, MD, Yeonjung Kim, MD, Sea Won Oh, BSc, Seong-Hae Jeong, MD, Ji Soo Kim, MD, PhD Abstract: A 27-year-old man with MELAS 3243 mutation developed a right homonymous hemianopia, left beating nystagmus, and impaired smooth pursuit (SP) to the left. Intermittently, the left beating nystagmus changed to right beating with rightward eye and head deviation and associated altered mental status. Each episode lasted several minutes. MRI revealed restricted diffusion in left parieto-temporo-occipital cortices. During the ictus, elec-troencephalogram showed epileptic discharges in the left temporo-occipital region, and single photon emission computed tomography demonstrated hyperperfusion in the same area. The interictal left beating nystagmus may be ascribed to contralesional bias of SP imbalance since the parieto-temporo-occipital region is involved in the generation of SP. The ictal right beating nystagmus and rightward head and eye deviation indicate coactivation of the SP areas and parietal eye field. This report documents the novel co-occurrence of pursuit-paretic and epileptic nystagmus. Journal of Neuro-Ophthalmology 2012;32:135-138 doi: 10.1097/WNO.0b013e31824d2a15 © 2012 by North American Neuro-Ophthalmology Society The presence of nystagmus usually indicates a lesion invol-ving the brainstem or cerebellum (1). Rarely, cerebral hemispheric lesions give rise to nystagmus. In pursuit-paretic nystagmus, lesions involving the human homologues of medial temporal (MT) and middle superior temporal (MST) areas in monkeys induce an imbalance favoring con-traversive smooth pursuit (SP), and resultant nystagmus beat-ing toward the side of the lesion (2,3). In contrast, epileptic nystagmus has been ascribed to irritation of the cortical areas involved in the generation of saccades or SP (4,5). We report pursuit-paretic and epileptic nystagmus in a MELAS patient whose MRI demonstrated an area of restricted diffusion involving left parieto-temporo-occipital cortices. CASE REPORT A 27-year-old man with known MELAS 3243 mutation complained of dizziness and difficulty with vision after drinking alcohol heavily. The diagnosis of MELAS was made 4 years previously when, again after heavy drinking, he developed visual blurring, left homonymous hemianopia, and headache. MRI showed high T2 signal intensities in the right occipital cortex, and genetic testing confirmed the diagnosis of MELAS. His visual field deficit resolved. Two years ago, the patient suffered status epilepticus after drinking alcohol. He had a younger brother with the same MELAS mutation. General physical examination showed normal vital signs but a short and thin body habitus. On visual field testing, the patient had a right homonymous hemianopia. Eye movements showed spontaneous left beating nystag-mus in primary gaze (Fig. 1A), which increased on left-ward aze. (See Video 1, Supplemental Digital Content 1, http://links.lww.com/WNO/A33. Video recording shows interictal spontaneous left beating nystagmus with fixation, which increases during leftward gaze. During the ictus, the nystagmus changes into right beating with right-ward eye deviation.) The patient also had a receptive (Wernicke) aphasia, as well as optic ataxia, simultagnosia, acalculia, agraphia, finger agnosia, and right-left disorien-tation, findings consistent with Balint and Gerstmann syndromes. Horizontal saccades appeared to be normal, but horizontal SP was impaired in both directions, left Department of Neurology (SYC, SWO, JSK), Seoul National Uni-versity College of Medicine, Seoul National University Bundang Hospital, Seoul, Korea; Department of Neurology (YK), Asan Med-ical Center, University of Ulsan College of Medicine, Seoul, Korea; and Department of Neurology (S-HJ), Chungnam National University Hospital, Chungnam National University College of Medicine, Daejeon, Korea. The authors report no conflict of interest. Supplemental digital content is available for this article. Direct URL citations appear in the full text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.jneuro-ophthalmology.com). Address correspondence to Ji Soo Kim, MD, PhD, Department of Neurology, College of Medicine, Seoul National University, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi-do, 463-707, Korea; E-mail: jisookim@ snu.ac.kr Choi et al: J Neuro-Ophthalmol 2012; 32: 135-138 135 Original Contribution Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. greater than right. (See Video 2, Supplemental Digital Content 2, http://links.lww.com/WNO/A34. Video re-cording shows interictal spontaneous left beating nystag-mus with fixation, which increases during leftward gaze. During the ictus, the nystagmus changes into right beat-ing with rightward eye deviation.) Intermittently, the patient suddenly exhibited altered mental status and rightward head turning. At this time, the left beating nystagmus changed to right beating with rightward eye deviation (Fig. 1B; see Video 1, Supplemental Digital Content 1, http://links.lww.com/WNO/A33). Each epi-sode lasted several minutes and recurred several times. MRI of the brain disclosed restricted diffusion in left parieto-temporo-occipital lobes (Fig. 2A, B). Single photon emission computed tomography demonstrated hyperperfu-sion in the corresponding area (Fig. 2C). Electroencephalo-gram (EEG) showed epileptiform discharges in the left temporo-occipital cortices (Fig. 3). The patient was treated with 1,000 mg of phenytoin a day and then switched to 1,000 mg of levetiracetam a day for more than 15 days. The seizure attacks dis-appeared 5 days later with the resolution of epileptiform discharges on follow-up EEG. Twenty days later, the patient was discharged with mild aphasia and right FIG. 1. Video-oculography showing left beating nystagmus between the ictus (A), which intermittently changes into right beating nystagmus (B). Upward deflection indicates rightward and upward eye motion in each tracing. Note the different scales for eye movements. LH, horizontal position of left eye. FIG. 2. A. Diffusion-weighted imaging demonstrates area of restricted diffusion in the left temporo-parieto-occiptal region. B. Apparent diffusion coefficient maps confirms restricted diffusion. C. Ictal single photon emission computed tomography shows hyperperfusion in the left temporo-parieto-occiptal region. 136 Choi et al: J Neuro-Ophthalmol 2012; 32: 135-138 Original Contribution Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. homonymous hemianopia but without spontaneous nys-tagmus or impaired SP. DISCUSSION The cerebral cortex contributes to voluntary control of eye movement in human, including SP (1). The frontal eye fields, supplementary eye fields, and posterior parietal cortex are all involved in the control of horizontal SP in monkeys and humans (1,6). Anatomic regions, MT and MST areas, are important parts of the neural pathways controlling hor-izontal SP (1,7). Patients with hemispheric lesions may show horizontal nystagmus along with horizontal SP asymmetry (1,2). The nystagmus is usually of low amplitude with the slow phase away from the side of the lesion (3). Because these patients also show impaired SP more to the lesion side, this nystag-mus is ascribed to an imbalance in horizontal SP tone and has been termed as "pursuit-paretic nystagmus" (3,7). The lesion in our patient involved the human homologue of MT and MST areas (Brodmann areas 19, 37, 39) (8). Accordingly, impaired SP, more to the left, and the left beating nystagmus between the ictus may be explained by the temporo-parieto-occipital abnormality detected on MRI. The left beating nystagmus in our patient intermittently changed to right beating nystagmus with rightward eye and head deviation and altered mental status. EEG revealed ictal discharges in the left temporo-occipital area (T5-O1), confirming seizure activity. Epileptic nystagmus has been attributed to irritation of the cortical areas involved in gen-erating eye movements. Activation of centers involved with either saccadic or SP could generate contralesional nystag-mus (4,5). When the saccadic areas are stimulated, the epi-leptic nystagmus has a decreasing slow-phase velocity (SPV) and occurs only in the contraversive hemifield, without crossing the midline (4). In contrast, the epileptic nystag-mus generated from the SP region has a linear SPV with the eyes crossing the midline. Irritation of the SP region would induce ipsiversive deviation of the eyes and corrective quick phases returning the eyes near to the midline (4,9,10). Our patient had features of both contraversive eye deviation and nystagmus with linear SPV. Yet, the nystag-mus occurred only in the contraversive hemifield without crossing the midline. The parietal eye fields and human homologue of MT/MST are located near each other, and both could be affected by seizure activity. Our patient showed sharp waves and spikes of 8-10 Hz on EEG. It is known that 10 Hz of epileptic discharge is the minimum frequency required to generate nystagmus (4). Reports of eye movement disorders in MELAS patients are rare. Shinmei et al (11) described persistent ocular motor dysfunction (including downbeat nystagmus, square wave jerks, impaired SP, and hypermetric and hypometric saccades) in patients with MELAS and normal MRI. In contrast, with anticonvulsant therapy, our patient showed resolution of nystagmus and SP asymmetry and had an abnormal MRI. While the exact mechanism remains un-known, the stroke-like episodes in MELAS have been as-cribed to neuronal hyperexcitability from abnormal mitochondrial RNA and diffuse endothelial necrosis of the small vessels in the brain (12). REFERENCES 1. Leigh RJ, Zee DS. The Neurology of Eye Movement. 4th ed. Oxford, England: Oxford University Press, 2006. 2. Sharpe JA, Lo AW, Rabinovitch HE. Control of the saccadic and smooth pursuit systems after cerebral hemidecortication. Brain. 1979;102:387-403. 3. Sharpe JA. Pursuit paretic nystagmus. Ann Neurol. 1979;6:458. 4. Kaplan PW, Tusa RJ. Neurophysiologic and clinical correlations of epileptic nystagmus. Neurology. 1993;43:2508-2514. FIG. 3. Ictal EEG discloses sharp waves and spikes of 8-10 Hz in the left temporo-occipital region (T5, 01). EEG, electro-encephalogram. Choi et al: J Neuro-Ophthalmol 2012; 32: 135-138 137 Original Contribution Copyright © North American Neuro-Ophthalmology Society. 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