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Show Journal of Neuro- Ophthalmology 21( 4): 264- 265, 2001. © 2001 Lippincott Williams & Wilkins, Inc., Philadelphia Original Contribution Seesaw Nystagmus Following Whole Brain Irradiation and Intrathecal Methotrexate John A. Epstein, MD*, Mark L. Moster, MDf, and Michael Spiritos, MD$ A patient developed pendular seesaw nystagmus ( SSN) 14 months after receiving radiation and intrathecal methotrexate for intracranial spread of systemic lymphoma. The nystagmus followed severe visual loss from damage to the optic nerves and chiasm. This case expands the causes of pendular SSN and lends further support to the notion that focal midbrain lesions may not be a prerequisite for its development. Key Words: Seesaw nystagmus- Radiation- Nystagmus- Lymphoma- Methotrexate. Seesaw nystagmus ( SSN) is a rare form of nystagmus characterized by alternating elevation and intorsion of one eye and simultaneous depression and extorsion of the opposite eye. Conditions associated with SSN include parasellar or suprasellar masses such as pituitary adenoma and craniopharyngioma, upper brain stem stroke, severe head trauma, septo- optic dysplasia, syringobulbia, Arnold Chiari malformations, multiple sclerosis, congenital achiasma, and loss of vision alone secondary to cone- rod dystrophy and retinitis pigmentosa ( 1). In many of these disorders, damage to the rostral brainstem has been demonstrated or presumed ( 2). However, the fact that congenital achiasma and cone- rod dystrophy can, by themselves, cause SSN, suggests that midbrain damage is not required to produce this nystagmus ( 3). We present a patient with radiation and chemotherapy- induced optic neuropathy and chiasmal involvement with SSN but without radiologic evidence of focal lesions in the brainstem. CASE STUDY A 64- year- old woman was diagnosed with diffuse large cell lymphoma of the pleura, mesentery and multiple bones and treated with 6 cycles of chemotherapy, * tDepartment of Neurosensory Sciences, Albert Einstein Medical Center; tDepartment of Neurology, Thomas Jefferson University School of Medicine; ^ Department of Internal Medicine, Abington Memorial Hospital. Address correspondence and reprint requests to Mark L. Moster, MD, Chairman, Dept. of Neurosensory Sciences, Albert Einstein Medical Center, 5501 Old York Road, Philadelphia, PA 19141; E- mail: mmoster@ aol. com including cyclophosphamide 1200 mg, vincristine 2 mg, and adriamycin 80 mg, followed by 4 doses of rituximab. Within one year of presentation, she developed seizures and right sixth and seventh nerve palsies. MRI revealed enhancement of the subependymal regions of the lateral ventricles and superior cerebellum, as well as focal meningeal enhancement of the right 7th and 8th nerve complex. Lumbar puncture revealed malignant lymphocytes. She received six 12- mg doses of intrathecal methotrexate ( MTX) via Ommaya reservoir, and whole brain irradiation ( XRT), 10 fractions of 300 cGy for a total of 3000 cGy. MRI two months later showed marked reduction in the CNS lesions. Neuro- ophthalmologic examination was performed for a two- month history of progressive visual loss OS that occurred eight months after this treatment. Visual acuity was 20/ 20 OD and count fingers OS with a 2- 3+ afferent pupillary defect, and trace optic pallor OS. Visual fields showed diffuse loss OS with hemianopic loss OD ( Fig. 1). There was no nystagmus. MRI showed enhancement of the left side of the optic chiasm and both optic nerves, left greater than right ( Fig. 2). Lumbar puncture revealed normal cerebrospinal fluid. The patient was diagnosed with optic neuropathy and chiasm-opathy induced by radiation and, possibly, methotrexate. After progressive worsening of vision OU, she was treated with Solumedrol 1 gm intravenously x2, 30 treatments of hyperbaric oxygen, and Coumadin ( Bristol Myers Squibb, Princeton NJ). Visual acuity stabilized at 20/ 40 OD and hand motions OS. However, 4 months later, Coumadin was discontinued after she fractured her hip. FIG. 1. Visual fields demonstrating diffuse loss OS with hemianopic loss OD. 264 SEESAW NYSTAGMUS FOLLOWING WHOLE BRAIN IRRADIATION 265 FIG. 2. T1 weighted MRI image, performed eight months after XRT and MTX treatment, demonstrates posterior optic nerve enhancement ( left greater than right) and left- sided chiasmal enhancement. Two months after discontinuing Coumadin, her vision OD declined precipitously to 20/ 200 OD and hand motions OS. Pendular seesaw nystagmus in primary position was now noted. The patient was alert and had no focal neurological deficits suggestive of a midbrain lesion. Brain MRI, performed 18 months post XRT/ MTX treatment, showed prominent periventricular white matter changes consistent with the effects of radiation and MTX, as well as atrophy of the optic chiasm and adjacent structures ( Fig. 3). DISCUSSION Two patterns of SSN have been described: 1) Jerk SSN, associated with lesions in the region of the interstitial nucleus of Cajal ( 1), and 2) pendular SSN, associated with parasellar or chiasmal mass lesions ( 4). In the past, there has been the impression that sellar lesions caused pendular SSN by pressure on the midbrain ( 5). However, brainstem disease may not be a prerequisite to pendular SSN, as exemplified by many case reports of this form of nystagmus occurring in patients with retinitis pigmentosa or cone- rod dystrophy ( 3,6) and no clinical or imaging evidence of brain stem disease. Our case, which shows midbrain atrophy but no focal or clinical abnormalities referable to the brain stem, adds support to that concept. It has been proposed that visual loss inactivates the normal recalibration mechanism for eye movements during head tilt through a visual- vestibular pathway ( 2). Although intrathecal chemotherapy with MTX and cy-tosine arabinoside has been abundantly reported to cause blindness and demyelination of the optic nerves and chiasm ( 7,8,9), no previous cases have described SSN. Our case adds radiation and MTX as a possible etiology for SSN and lends further support to the notion that imaging evidence of a focal midbrain lesion is not a prerequisite for SSN. FIG. 3. FLAIR MRI image, performed 18 months after XRT and MTX treatment, demonstrating increased signal in the cerebral hemispheric white matter. A: secondary to radiation and MTX. B: atrophy of optic nerves, chiasm, and midbrain without focal lesions. REFERENCES 1. Leigh J, Averbuch- Heller L. Nystagmus and related ocular motility disorders. In: Miller NR, and Newman NJ, eds. Clinical Neuro- Ophthalmology. 5th ed. 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