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Show f. Clin. Neun>-ophthdlmol. 1: 185-IIN, IQ81 Primary Position Upbeat Nystagmus Another Central Vestibular Nystagmus? TSUTOMU NAKADA, M.D. MICAHEL P. REMLER, M.D. Abstract Recent studies of the vestibulo-ocular reflex have revealed a distinct pathway from the anterior semicircular canal to the contralateral oculomotor nucleus via the superior vestibular nucleus. Axons of this pathwa\' ascend in the brachium conjunctivum, while axons of the other semicircular canal pathways ascend in the medial longitudinal fasciculus (MLF). We report two cases of primary position upbeat nystagmus where lesions of the brachium conjunctivum were suggested by computed tomography (eT) scans, One of these lesions was confirmed at autopsy. We concluded that primary position upbeat nystagmus, like downbeat nystagmus, is a type of central vestibular nystagmus resulting from an imbalance of vertical vestibulo-ocular reflex activity. Primary position upbeat nystagmus is a rare form of nystagmus in which the fast phase is directed upward on forward gaze. Although the pathological causes of vertical nystagmus are diverse, some cases of primary position upbeat nystagmus result from localized structural brain lesions. I -." Daroff and Troost classified primary position upbeat nystagmus into two types: coarse, large-amplitude primary position upbeat nystagmus which increases in intensity on upward gaze (type 1); and small-amplitude primary position upbeat nystagmus which increases in intensity on downward gaze (type 2). I They proposed the anterior vermis as the lesion responsible for type I primary position upbeat nystagmus and the lower brain stem for type 2. Gilman et a!. studied vertic.ll pursuit in a case of primary position upbeat nystagmus and concluded that the lower brain stem was the site of the responsible lesion.~ Schatz et a!. had a case of primary position upbeat nystagmus with metastatic neoplasm involving the medulla." Troost et a!. described a case of primary position From the Department of Neurolo~y. University (If C~lif(lrni.I, Davis; and the Veterans Administration M('dic~1 Lenler, M~r· tinez, California. September 1981 upbeat nystagmus associated with internuclear ophthalmoplegia due to a brain-stem glioma invading the upper part of the fourth ventricle on CT scan." We observed two cases of primary position upbeat nystagmus. Both patients had a midline metastatic cerebellar tumor involving the brachium conjunctivum. We present their clinical, radiological, and pathological findings. Patient 1 A 65-year-old white male presented with a 2week history of progressive ataxia and mental confusion. He had had a pneumonectomy for adenocarcinoma 7 years previously. On admission, he was oriented to self and place, but could not give his age or the date. His speech was normal, but his memory was moderately impaired. He showed upbeat nystagmus in the primary position, which increased in amplitude on upward gaze. The frequency and amplitude of the nystagmus L)n forward gaze were approximately 2 beats/second and 3 0 , respectively. He also had mild horizontal endpoint nystagmus bilaterally. His saccadic eve movements were clinically n~rmal in all directiL)~s. His horizontal smooth pursuit eye mLwements appeared to be within normal limits. The pupils were equal, round, and reactive to light. Other cr.mi.ll nerves were within norm.ll limits. His strength W.1S normal in all extremities, but .1 mild intention tremor and rebound were L,bserved in h)th upper extremities. He could nl)t st..lI1d l)r sit without support and often fell tL) the right. His deep tendon reflexes were normal .1nd the pl.mt.H responses were equiVl)C.11 bil.lter.llly. CT br.lIn SColn showed a midline Il)w density ce·rebl'll.H Illass .IJj.lcent tn the fourth ventricle (Fig. I). The lesinn .1ppl'.Hl'd tl) involve the left br.lchium Cl)nlunctivum Steroid and radiation therapy were begun. His .1taxia diminished and he was able to stand briefly by himself. His upbeat nystagmus decreased in amplitude. CT brain scan repeated 5 weeks later revealed .1 large discrete cystic lesion in the left cerebellar hemisphere with displacement of the fourth ventricle. He died 2 months later of aspiration pneumonia. 185 Upbeat Nystagmus Figure 1. An unenhanced CT scan of case 1 shows a midline low-density cerebellar lesion involving the left brachium conjunctivum (arrow). Autopsy A cystic tumor was located primarily in the left cerebellar hemisphere adjacent to the vermis (Fig. 2). The lesion involved the left dentate nucleus, left brachium conjunctivum, and part of the nodulus. The wall of the cystic lesion contained tumor cells, which were consistent with adenocarcinoma. The surrounding area showed edema and gliosis. Multiple microscopic sections throughout the brain stem revealed no other lesions. Patient 2 A 44-year-old white male presented with the acute onset of headache, mental confusion, and unsteady gait. A diagnosis of disseminated melanoma had been made 7 months previously. On admission, he was oriented to self and place, but mildly confused with time. His speech was slightly dysarth ric. He preferred to look downward because of the coarse upbeat nystagmus. The frequency and amplitude of the nystagmus on forward gaze were approximately 1.5 beats/second and 40 , n'spectiv('ly. Th(' amplitude increased on upwJrd gaze. His saccadic ('y(' movements were clinically normal in all directions. His horizontal ~rTl(loth pursuit eye mov('ments appeared to be 186 within normal limits. The pupils were equal, round, and reactive to light bilaterally. Other cranial nerves were unremarkable. He did not have any weakness in his extremities, but rapid alternating movements were poor, especially in his right hand. He showed a mild dysmetria with his left hand, but did not have obvious rebound or intention tremor. He could not stand without support and showed severe truncal and gait ataxia. His deep tendon reflexes were normal bilaterally, and the plantar responses were flexor. CT brain scan showed a mixed-density mass surrounding the markedly distorted fourth ventricle. The lateral and third ventricles were dilated. The brachium conjunctivum appeared to be involved bilaterally (Fig. 3). Following steroid and radiation therapy, his mental status improved and his gait ataxia diminished. Primary position upbeat nystagmus persisted. He was discharged at his request. No further follow-up was obtained. Discussion An imbalance in pursuit tonus has been suggested as the cause of primary position upbeat nystagmus.2 ,6 Subsequent studies, however, criticized the theory of "pursuit defect nystagmus" and Journal of Clinical Neuro-or!~:~.llmology September 1981 Figure 2. This horizontal section of the brain of case 1 shows a cystic lesion wIthin the left cerebellar hemisphere extending deep into the left dentate nucleus and brachium conjunctivum. Figure 3. An enhanced CT scan of case 2 shows ,1 midline mixed-density cerebellar lesion involving the brachium conjunctivum biiater"lly (",rows). N"kadd, Remler 187 Upbc.Jt Nyst.Jgmus Figure 4. Schemdllc represenldtion of Ihe exnl.Jtory .Jnlenor sem;c;rcuIM cdndl vesllbulo-oculM r<'flex p.Jlhw.Jy. III-Oculomotor nlldeus. VN-Vl·stlbul.n nur!eus. 5-supenor nur!eus, Behr. H hllJll1 lllnllJrll tiVl11ll, "R-t.,uperiOf redus, 1()-infC'rior "h1Jqlle, "C-dnl",ior semicircular canal. pursuit ,lsymmetry seen with spontaneous nystagmus WdS intf'rprf'tf'd dS the result rather than the cause" " In thf'ir mdjor review of downbeat nystagmus, Baloh ,md Spooner examined the vestibulo-ocular reflf'x p,lthw,lyS dnd postulated downbeat nystagmus ,1S ,1 form of central vestibular nystagmus7 According to that concept, the spontaneous toxic discharges of the ampullary nerves of semicircular canals are passf'd on to the oculomotor nuclei through the vestibulo-ocular reflex pathways. The lack of neuronal activity in one direction results in a tonic drift in the opposite direction. A correcting fast saccade produces nystagmus. The excitatory pathways of vestibulo-ocular reflex have been studied extensively in the rabbit.~· 10 The anterior semicircular canal pathway is shown in Figure 4. The excitatory impulses from the anterior semicircular canal are relayed through the superior vestibular nucleus to the contralateral oculomotor nucleus via the brachium conjunctivum. Excitation of the anterior semicircular canal produces contraction of the ipsilateral superior rectus and contralateral inferior oblique muscles. III Theoretically, interruption of this reflex pathway, especially with bilateral lesions sparing the other semicircular canal pathways, induces a tonic imbalance, which results in a slow downward drift and upbeat nystagmus. Irrigation of the external auditory canal with cold water transfers a temperature gradient to the inner ear. The horizontal semicircular canal devel- References 1. Daroff, R.B., and Troost, B.T.: Upbeat nystagmus. rA.M.A. 225: 312, 1073. 2. Gilman, N., Baloh, R.W., and Tomiyasu, U.: Primary position upbeat nystagmus-A clinicopathologic study. Neurology 27: 294-298, 1977. 3. Pawl, R.P.: Upbeat nystagmus. rA.M.A. 226: 565, 1973. 4. Schatz, N.J., Schlezinger, N.5., and Berry, R.G.: Vertical up-beat nystagmus on downward gaze-A clinical pathologic correlation. Neurology 25: 380, 1975. 5. Troost, BT, Martinez, J., Abel, LA., and Heros, R.C.: Upbeat nystagmus and internuclear ophthalmoplegia with brainstem glioma. Arch. Neurol. 37: 453-456, 1980. o. Mehdorn, E., Kommerell, G., and Meienberg, 0.: Primary position vertical nystagmus-'Directional preponderance' of the pursuit system? Albrecht Von Graefes Arch. Klin. Exp. Ophthalmol. 209: 209-217, 1979. 7. Baloh, R.W., and Spooner, J,W.: Downbeat nystag-ops the largest temperature gradient because it lies closest to the stimulus, In supine position with head tilted 30° up, irrigation with cold water decreases the tonic discharge of the ampullary nerves, which results in slow drift toward the irrigated side and horizontal nystagmus with the fast phase directed to the opposite side. In the same position, the anterior semicircular canals are less affected and the posterior semicircular canals are hardly affected at all. II The effects on the two horizontal semicircular canals are in opposition, while those on the anterior semicircular canals are in the same direction. Therefore, bilateral irrigation produces the cancellation of the horizontal semicircular canal influences and allows the enhanced minor anterior semicircular canal effects to emerge. Bilateral irrigation is known to produce vertical nystagmus. 12 This well-known caloric test provides a model of primary position upbeat nystagmus. Our patient 1 had a left brachium conjunctivum lesion at autopsy. Our patient 2 showed large lowdensity lesion involving the brachium conjunctivum bilaterally on CT scan. The case of Gilman et al. involved all the vestibular nuclei. 2 The patient of Troost et al. had a tumor in the upper part of the fourth ventricle on CT scan,s so that the brachium conjunctivum was very likely to be affected bilaterally. Therefore, it is quite plausible that all these patients manifested basically the same imbalances of tonic vertical vestibulo-ocular activity. In conclusion, we believe that primary position upbeat nystagmus is another form of central vestibular nystagmus. The interruption of the neural pathway from the anterior semicircular canal produces the vertical tonic imbalance. The lesion responsible is most likely to be in the brachium conjunctivum. 11/ 00 I I I ~:orn I I VN AC 11>8 Journal of Clinical Neuro-ophthalmology mus-A type of central vestibular nyst.l~mu~. Neurology 31: 304-310, 1981. 8. Daroff, R.B., Dell'Osso, L.F., .1Ild Abel. L.A.: 1'1Ir~uit defect nystagmus. Ann. Neural. 6: 458-45Q, 1Q7Q. 9. Ito, M., Nishimaru, N., and Yam.lmoto, M.: P,lthways for the vestibulo-ocular reflex excit,ltil'n .!rising from semicircular canals of rabbit~. £J.p. Br.lin Res. Z4: 257-271. 1970. 10. Yamamoto, M., Shimoyama, j., .1Ild Hi~hstein, S.M.: Vestibular nucleus neurons relaying excitation from the anterior canal to the oculomotor nucleus. Br.lin Res. 148: 31-42. 1978. 11. Dejong, R.N.: The Neurologic £J..lmin.Jtion (4th ed.). Harper & Row, New York, 1979, pr. 210-218. 12. Bender. M.B.: Brain control of conjug.lte horizontal September 1981 .lnd vertic.l1 eye movements-A survey of the structur. ll ,md functional correlates. Brain 103: 23-69. 1980. Acknowledgments The authors thank Drs. W.e. Ellis and R.e. Burt for their help in the patholo~ical evaluation and Mrs. H. Nakada for the illustration. Write for reprints to: Tsutomu Nakada, M.D., Department of Neurology, University of California, Davis. Veterans Administration Medical Center. 150 Muir Road, Martinez. California 94553. 189 |
