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Show Journal of Clinical Neur~thalmology 7(2): 104-107, 1987. Congenital Ocular Motor Apraxia in Twins Findings with Magnetic Resonance Imaging Mark S. Borchert, M.D., Alfredo A. Sadun, M.D., Ph.D., Jonathan D. Sommers, M.D., and Kenneth W. Wright, M.D. © 1987 Raven Press, New York A pair of identical twins, whose features met Cogan's classic description of congenital ocular motor apraxia, were examined. Each had an absence of willed horizontal saccades and demonstrated classic head thrusting. Magnetic resonance imaging revealed hypoplasia of the corpus callosum. Fourth ventricle enlargement and generalized cerebral hypoplasia were also present but were more pronounced in the sibling with the more delayed motor development. The significance of these findings is discussed in light of our understanding of the control mechanism of volitional eye movements. Key Words: Cerebral hypoplasia-Corpus callosumHead thrusting-Ocular motor apraxia. From the Department of Ophthalmology, University of Southern California School of Medicine, and the Estelle Doheny Eye FlJund'ati0a, Los Angeles, California. Address correspondence and reprint requests to Kenneth W. V\:r~f.ht, MD., Divisi?n of OphUWil\oki:gf~.!Chiidrens Hospital .)j: L{)~ Ang",:%, 46,,0 SunsetBouleva~i: Los Angeles, CA 90027, U.S.A. 104 Congenital ocular motor apraxia has been described by Cogan (1) as a syndrome consisting of the absence of willed horizontal saccades in the presence of normal vertical and random saccades. Cogan also described the use of peculiar head thrusts to initiate a change in the direction of horizontal gaze. These deficits tend to improve with age (1,2). Congenital ocular motor apraxia usually occurs sporadically, although familial cases have been reported (3-5). A pathologic lesion has not been described, although several neuroradiologic reports have suggested lesions of the cerebellum, brainstem, and corpus callosum (3,6,7). Herein, we describe two cases of congenital ocular motor apraxia in identical twins; brain abnormalities were identified using magnetic resonanc.e imaging. CASE REPORTS A pair of 20-month-old monozygotic #l.l~ twins, D.N. and M.N., were referred for evalu,;. tion of peculiar eye movements. They were premature (at 32 weeks gestational age), with a)iI:Jlt weight of 1,830 g for D.N. and 1,340 g for M.N.. Delivery was by cesarean section and both infants initially required endotracheal intubation and,,__ tilation for apnea of prematurity. Apg~~ were recorded as 8 at 1 min and 9 at 5 mfn&lr' N.M., and 3 at 1 min and 4 at 5 min for D.N. At.6· months of age, developmental delay was npted\, associated with mild motor retardation. At tl.Ie time of referral, D.N. was walking normally.~ had more advanced motor skills than did hiS twiI brother, who had not yet attempted walking. 8of:I infants had normal fixation and ability to foUQ" vertically moving targets. Change of horizontal. gaze, however, could be initiated only by head thrusts, as described by Cogan (1). Vestibular CONGENITAL OCULAR MOTOR APRAXIA 105 stimulation resulted in the eyes becoming fully abducted or adducted, without the normal fast phase of nystagmus in either direction. The remainder of the ophthalmic examination was normal. Interestingly, the patients father appeared to have subtle abnormalities in saccades, but he would not allow us to evaluate these. Moreover, he did not permit photographs of the patients faces, although he did allow us to obtain magnetic resonance imaging scans of their heads. Magnetic resonance imaging scans of M.N. showed marked enlargement of the fourth ventricle (Fig. 1); this was also present, albeit much less pronounced, in D.N. M.N. also had generalized enlargement of the sulci, indicating cerebral hypoplasia (Fig. 2); again this was present but less evident in D.N. Both patients had thinning of the corpus callosum, once again more pronounced in M.N. than D.N. (Figs. 3 and 4). This was best seen on the sagittal sections, where the hypoplasia was more pronounced anteriorly than in the splenium. T2weighted images were not obtained. A follow-up examination could not be obtained. COMMENT Since the initial description of congenital ocular motor apraxia by Cogan (1) in 1952, there has been FIG. 1. Axial T1-weighted magnetic resonance imaging scan of patient M.N. showing enlargement of the fourth ventricle (arrow). FIG. 2. Sagittal T1-weighted magnetic resonance imaging scan of M.N. demonstrating sulcus enlargement, consistent with generalized cerebral hypoplasia. a great deal of speculation over the sites of possible anatomic lesions. Congenital ocular motor apraxia is thought to involve primarily the saccadic system, and saccades are believed to originate in frontal area 8. Therefore, Brodmann's area 8 was the site suggested by several authors to be anomalous (2,8,9). Ablation of area 8 in monkeys, however, caused only subtle decreases in the size FIG. 3. Sagittal T1-weighted magnetic resonance imaging scan of M.N. showing very thin corpus callosum; this is most pronounced anteriorly (arrow). JClin Neuro-ophthalmol, Vol. 7, No.2, 1987 106 M. S. BORCHERT ET AL. FIG. 4. Sagittal T1-weighted magnetic resonance imaging scan of D.N. showing callosum hypoplasia; this is less marked than that in M.N. (Fig. 3). and frequency of saccades (10). Zee and colleagues (11) demonstrated further complexity of the syndrome by performing systematic eye movement analysis on three older patients with congenital ocular motor apraxia. They found that these patients had normal saccadic velocities, indicating a supranuclear lesion. More important, they had a 3- to 10-s delay in initiating saccades, and, the more volitional the saccade, the greater the latency. In addition, Zee et al. (11) found a breakdown of smooth pursuit into small catch-up saccades. These findings are suggestive of parietal lobe lesions that cause an increased latency of contralateral saccades and impair ipsilateral smooth pursuit (12,13). Moreover, bilateral area 7 lesions cause an acquired ocular motor apraxia (14). As there are numerous transcallosum interconnections between parietal lobes, callosum dysgenesis has been proposed as a likely etiology for congenital ocular motor apraxia (3). Using computerized tomography, Orrison and Robertson (3) found partial agenesis of the corpus callosum in two patients with congenital ocular motor apraxia. Both of our patients also demonstrated callosum hypoplasia on magnetic resonance imaging, thus corroborating their findings. Eda and colleagues (7) argued that the findings OfQL;110SU~. agenesis may simply represent the mOle.,w:rdc~;p;;ead:eNS malformations frequently JClin Neuro-ophthalmol, Vol. 7, No.2, 1987 associated with aplasia of the cerebellar vermis. They described four cases with vermis agenesis, as suggested by enlargement of the fourth ventricle. We also found significant enlargement of the fourth ventricle in the twin who developed other motor systems more slowly. A genetic mode of inheritance has been suggested based on one previous report of twins with congenital ocular motor apraxia (15) and one report of a father and daughter who had congenital ocular motor apraxia (16). Recently, an X-linked syndrome characterized by congenital contractures, muscle atrophy, and ocular motor apraxia has been described (17), lending support to the theory that classic congenital ocular motor apraxia may just be one manifestation of a more extensive inherited CNS disease. This is the first report of magnetic resonance imaging in patients with congenital ocular motor apraxia. The three significant findings in this study were collosum hypoplasia, enlargement of the fourth ventricle, and mild generalized cortical hypoplasia. The present study demonstrates the efficacy of magnetic resonance imaging in defining lesions associated with congenital ocular motor apraxia. Magnetic resonance imaging has an advantage over standard computerized tomography scanning as there is no radiation, which is an important consideration when treating the pediatric age group. Additional magnetic resonance imaging studies of congenital motor apraxia patients may allow us to define more thoroughly a unifying lesion causative of this disease. REFERENCES 1. Cogan DG. A type of congenital ocular motor apraxia presenting jerky head movements. Trans Am Acad Ophthalmol OtolanjngoI1952;56:853-62. 2. Altrocchi PH, Menkes JH. Congenital ocular motor apraxia. Brain 1960;83:579-88. 3. Orrison WW, RQbertson We, Jr. Congenital ocular motor apraxia: a possible disconnection syndrome. Arch Neurol 1979;36:29-31. 4. Narbona J, Crisci CD, Villa I. Familial congenital ocular motor apraxia and immune deficiency. Arch NeuroI1980;37: 325. 5. Sachs R. Apraxie oculo-motrice congenitale de Cogan: A propos de trois noveaux cas dont deux dans la meme fratrie. Ann Oculist 1967;200:266-74. 6. Rendle-Shor.t J, Ap~let?n B, Peam J. Congenital ocular motor apraXIa: paedlatnc aspects. Aust Paediatr J 1973;9: 263-8. 7. Eda I, Takashima 5, Kitahara T, Ohno K, Takeshita K. Computed tomography in congenital ocular motor apraxia. Neuroradiology 1984;26:359-62. 8. Campbell WL, Zeller R. Congenital ocular motor apraxia in females. Arch Ophthalmol 1961;66:643-5. 9. Riopel ~A. Con/?enital ocular motor apraxia: report of a case with a review of the literature. Am J Ophthalmol 1963;55:511-4. CONGENITAL OCULAR MOTOR APRAXIA 107 10. Schiller PH, True SO, Conway JL. Deficits in eye movements following frontal eye-field and superior colliculus ablations. J NeuraphysioI1980;44:1175-89. 11. Zee OS, Yee RD, Singer HS. Congenital ocular motor apraxia. Brain 1977;100:581-99. 12. Sundqvist A. Saccadic reaction-time in parietal-lobe dysfunction. Lancet 1979;1:870. 13. Baloh RW, Yee RD, Honrubia V. Optokinetic nystagmus and parietal lobe lesions. Ann NeuroI1980;7:269-76. 14. Cogan DG. Ophthalmic manifestations of bilateral non-occipital cerebral lesions. Br JOphthalmoI1965;49:281-97. 15. Robles J. Congenital ocular motor apraxia in identical twins. Arch Ophthalmoll966;75:746-9. 16. Vassella F, Lutschg J, Mumenthaler M. Cogan's congenital ocular motor apraxia in two successive generations. Deu Med Child NeuroI1972;14:788-803. 17. Wieacker P, Wolff G, Wienker TF, Sauer M. A new Xlinked syndrome with muscle atrophy, congenital contractures, and oculomotor apraxia. Am J Med Genet 1985;20:597-606. J elin Neuro-ophthalmol, Vol. 7, No.2, 1987 |
