Clinical/Scientific Notes Periodic alternating nystagmus in a patient with MS S. Matsumoto, MD; Y. Ohyagi, MD; I. Inoue, MD; A. Oishi, MD; H. Goto, MD; T. Nakagawa, MD; T. Yamada, MD; and J.-I. Kira, MD Periodic alternating nystagmus (PAN) is a rare horizontal nystag- mus that periodically reverses its direction, usually about every 2 minutes. 1 Acquired PAN has been reported in various neurologic disorders, such as spinocerebellar ataxia, Arnold–Chiari malformation, 1-3 and MS. 4 We report a case of MS with PAN dem- onstrated by electronystagmography (ENG). Case report. A 39-year-old woman is presented. At age 27, she had a left optic neuritis. At age 31, she developed a moderate right limb and truncal ataxia and ataxic dysarthria with mild left hemi- paresis. MRI detected multiple lesions in the right middle cerebel- lar peduncle, right lateral midpons, and right ventral midbrain. She was diagnosed as having MS, improved with corticosteroid treatment, and continued to take low-dose prednisolone thereaf- ter. At age 39, she again developed a moderate truncal and, at this time, left limb ataxia, as well as an ataxic dysarthria. About 3 months later, she had a left visual loss and exacerbation of cere- bellar ataxia, and was admitted to our hospital. On admission, blindness of the left eye, absence of the left pupillary light response, normal right visual acuity, saccadic pur- suit, moderately ataxic dysarthria, moderate left limb ataxia, moderate truncal ataxia, brisk left tendon reflex, positive left Bab- inski reflex, and mild sensory disturbance in the right half of the body including the face were found. In addition, a spontaneous horizontal jerk nystagmus, whose amplitude was increased by lateral gaze, was found. Remarkably, her nystagmus reversed its direction every 1 to 2 minutes. Blood chemistry was normal. Nor- mal immunoglobulin (Ig) G index, no oligoclonal bands but slight elevation of the cell count (14/L, normal 5/L) were found in the CSF. MRI detected new lesions in the left optic nerve and left dorsolateral midpons. An auditory brainstem response (ABR) study showed a bilateral delay (right 2.53, left 2.40, normal 2.31 milliseconds) in the inter-peak latency between III and V, consis- tent with the pontine lesions. The left visual loss and cerebellar ataxia were markedly ame- liorated with high-dose corticosteroid treatment within a week after admission, while PAN in light gradually disappeared. How- ever, PAN in darkness was still observed thereafter. Her PAN in darkness was recorded by ENG 4 weeks after admission (figure). An approximately 110-second right-side nystagmus (see figure, A); approximately 10-second pause with low amplitude square-wave jerks (see figure, B); and an approximately 70-second left-side nystagmus (see figure, C) were recorded. The amplitude was larger in the right-side nystagmus (15° to 40°) than in the left-side nystagmus (10° to 15°). Periodicity was approximately 3 minutes (see figure, D). A caloric test with 20 °C water bilaterally evoked nystagmus that continued more than 180 seconds, indicating no canal pare- sis. However, visual suppression of the caloric nystagmus was bilaterally decreased (left 14%, right 21%, normal 50%). In addi- tion, optokinetic nystagmus (OKN) was not evoked bilaterally. Such good caloric responsiveness and diminished OKN are often reported in the patients with PAN. 1-3 Discussion. This is the first case of MS in which PAN is re- corded by ENG. The nodulus and uvula (NU) in the cerebellum control the time course of rotationally induced nystagmus (“veloc- ity storage” system). Dysfunction in the NU Purkinje cell activity causes PAN by prolongation of velocity storage and the instability of the vestibulo-ocular reflex (VOR). 5,6 Thus, in our case, the le- sions in the brainstem or cerebellum may affect the NU or their projections. Interestingly, the time span and amplitude of the left-side nystagmus were apparently shorter and smaller than those of the right-side nystagmus. This asymmetry of nature of the nystagmus may be due to the asymmetry of the lesions in brainstem or cerebellum, suggesting that the left VOR may be relatively more unstable than the right. Another point of interest in our case is the persistence of PAN in darkness after disappearance of PAN in light. In animal exper- iments, PAN is usually observed in darkness. 5,6 Jay et al. 7 reported a case in which PAN developing concomitantly with visual loss due to bilateral cataracts was cleared up after unilateral cataract surgery, suggesting that a latent PAN may have been manifested by the loss of visual fixation. It is therefore potentially possible that an involvement of the visual fixation pathway had mani- fested a latent PAN in our case. The left visual loss may not be the major cause, because unilateral visual loss itself does not cause PAN. 7 OKN and the visual suppression in the caloric test were bilaterally impaired. Thus, the brainstem lesions in our case might have affected the visual fixation pathway resulting in PAN in light. It is therefore necessary to check for PAN in cases of MS in the dark room, which might disclose a latent PAN. From the Department of Neurology (Drs. Matsumoto, Ohyagi, Inoue, Oishi, Yamada, and Kira), Neurological Institute; and the Department of Otolaryn- gology (Drs. Goto and Nakagawa), Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. Received July 5, 2000. Accepted in final form August 29, 2000. Address correspondence to and reprint requests to Dr. Yasumasa Ohyagi, Department of Neurology, Neurological Institute, Graduate School of Medi- cal Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812- 8582, Japan; e-mail: ohyagi@neuro.med.kyushu-u.ac.jp Figure. Electronystagmogram (ENG) recordings. (A) Right-side nystagmus; (B) low-amplitude square-wave jerks during the pause; (C) left-side nystagmus; (D) analy- sis of direction and amplitude of the nystagmus by a pseudo-differential recording. Eye position was monitored by electrode on temple with the referential electrode on forehead (EN100, NEC, Tokyo, Japan). Note that direction of the nystagmus is periodically reversed. 276 NEUROLOGY 56 January (2 of 2) 2001