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Show Journal ofNeuro- Ophthalmology 21( 1): 39- 41, 2001. © 2001 Lippincott Williams & Wilkins, Inc., Philadelphia Comparison of Clinical Associations of Patients With Vasculopathic and Idiopathic Downbeat Nystagmus Jeffrey L. Olson, MD, and Daniel M. Jacobson, MD Objectives: To perform a pilot study comparing age and vascular risk factors of patients with vasculopathic and idiopathic downbeat nystagmus ( DBN). Materials and Methods: We reviewed the case records of 57 patients with DBN evaluated between 1987 and 1999, and classified each patient into three groups: vasculopathic, idiopathic, and other known causes. We then compared age and five weighted established stroke risk factors in patients with vasculopathic and idiopathic DBN. Results: Of ten idiopathic cases, there were seven women and three men, ranging in age from 31 to 90 years ( median, 79 years). Of the nine vasculopathic cases, there were seven women and two men, ranging in age from 50 to 86 years ( median, 80 years). Using the Mann- Whitney U test, there was no significant difference between the two groups in terms of age ( p = 0.84) or vascular risk- factor profile ( p = 0.24). Conclusions: The lack of significant difference between the two groups for age and vascular risk factors supports the hypothesis that some idiopathic cases of DBN may be caused by strategically located and radiographically occult cerebral infarctions. Key Words: Downbeat nystagmus- Vascular risk factors- Stroke. In published case series ( 1- 4) of downbeat nystagmus ( DBN), the most common causes were cranio- cervical structural disorders, cerebellar degenerations, toxic and metabolic disorders, multiple sclerosis, and strokes. Despite the many known causes of DBN, the etiology remains undetermined in 5 to 44% of patients ( 1- 4). Our untested impression has been that many patients with idiopathic DBN are elderly with vascular disease. We postulated, therefore, that some cases of idiopathic DBN might be caused by occult strokes affecting the brainstem. To test this hypothesis, we performed the following Manuscript received June 8, 2000; accepted December 5, 2000. Presented in part at the Annual Meeting of the North American Neuro- ophthalmology Society, Mont Tremblant, Quebec, Canada, March 26- 30, 2000. From the Department of Medical Education ( JLO), and the Departments of Neurology and Ophthalmology ( DMJ), Marshfield Clinic, Marshfield, Wisconsin. Address correspondence and reprint requests to Daniel M. Jacobson, MD, Neuro- ophthalmology ( 4F- 2), Marshfield Clinic, 1000 North Oak Street, Marshfield, Wisconsin 54449. exploratory pilot study to compare age and vascular risk factors in patients with vasculopathic and idiopathic DBN. A similar clinical profile, if found, in these two groups might support a possible cerebrovascular etiology for patients who have no overt cause identified after initial investigation. METHODS We reviewed the case records of all patients with DBN evaluated by one of us ( DMJ) at a single institution between 1987 and 1999, and classified each patient into one of three groups: vasculopathic, idiopathic, and other known causes. We defined as vasculopathic those patients whose DBN was associated with other clinical signs, and radiographically verified changes, of cerebral infarction affecting the posterior fossa. After reviewing the literature, we compiled a list of other reported causes of DBN ( Table 1). We classified cases as other known causes if the patient had any of these associations. Finally, we defined as idiopathic those patients whose symptoms were recently acquired, who had no prior documentation in the medical record of DBN, and who had no known cause. We then compared age and five established stroke risk factors in patients with vasculopathic and idiopathic DBN. These risk factors- which included hypertension, coronary artery disease, atrial fibrillation, diabetes mel-litus, and cigarette smoking- were weighted using published relative risk data ( 5) ( Table 2). For each patient, we added the relative risk factor, if present, to derive a total vascular risk factor score. We then used the Mann- Whitney U test to compare the age and the derived composite vascular risk profile of the two groups. Although this study was retrospective, all patients were routinely queried about the presence of tobacco use and their general medical health, so that these variables were universally present in the medical records and available for abstraction. RESULTS Of the 57 patients with DBN evaluated during the study period, ten ( 18%) patients were classified as 39 40 J. L. OLSON AND D. M. JACOBSON TABLE 1. Reported causes and associations of downbeat nystagmus Cranio- cervical structural disorders Arnold- Chiari malformation Basilar invagination Paget disease Syringobulbia Dolichoectasia of the vertebrobasilar arterial system Tumors compressing the caudal brainstem Brainstem/ cerebellar disease Cerebellar degeneration Familial periodic ataxia Posterior fossa strokes Posterior fossa tumors Paraneoplastic syndromes Hydrocephalus Encephalitis Trauma Multiple sclerosis Toxic/ metabolic disorders Chronic ethanol exposure Wernicke encephalopathy ( vitamin Bx deficiency) Vitamin B12 deficiency Magnesium deficiency Lithium Phenytoin Carbamazepine Felbamate Morphine- barbituate combination Toluene Amiodarone Other Congenital Transient in the newborn Familial, isolated idiopathic. There were seven women and three men, ranging in age from 31 to 90 years ( median, 79 years). Downbeat nystagmus was neurologically isolated in all patients. As part of their work- up evaluation, all idiopathic patients underwent magnetic resonance imaging with special attention to the cranio- cervical junction. Diffusion or perfusion- weighted imaging was not performed. In addition, nine patients underwent magnesium determination and five patients underwent B12 level determination. None of these patients were exposed to toxins or medications known to be associated with DBN. Nine of 57 ( 16%) patients were classified as vasculo-pathic. There were seven women and two men, ranging in age from 50 to 86 years ( median, 80 years). Using the Mann- Whitney U test, there was no significant difference between the two groups in terms of age ( p = 0.84) ( Fig. 1) or vascular risk- factor profile ( p = 0.24) ( Fig. 2). TABLE 2. Stroke risk factor relative risk Risk factor Relative risk Hypertension Coronary heart disease Atrial fibrillation Diabetes mellitus Cigarette smoking 4.0 2.2 2.9 1.7 1.7 100 g 75- ( Q 0) o 50- 25H Idiopathic Infarction FIG. 1. Comparison of ages of 10 patients with idiopathic downbeat nystagmus and nine patients with vasculopathic ( indicated by infarction) downbeat nystagmus. The median ages of 79 years in the idiopathic group and 80 years in the vasculopathic group are represented by the horizontal bar in each column and are not significantly different ( p = 0.84). DISCUSSION Despite the various associations of DBN reported in the literature, the cause remains undetermined in a substantial proportion of cases. We were unable to assign a specific cause of DBN in 18% of the patients in our series. This frequency is consistent with the incidence of idiopathic cases identified in other large series of patients with DBN ( 1- 4). It is possible, however, that some cases classified as idiopathic might have shown small infarcts ( i. e., lacunar) if diffusion or perfusion- weighted magnetic resonance imaging was performed. It seems unlikely that this factor contributed substantially, if at all, to the misclassification of idiopathic patients, because none of them had other signs of posterior fossa injury. In our pilot study, we found that idiopathic patients were generally elderly and possessed a similar vascular risk profile as those patients who have suffered posterior fossa strokes that caused DBN. The previously reported large series of patients with DBN did not provide information regarding vascular risk factors or age specifically in idiopathic cases ( 1- 4). 7.5i £ P 5.0 .* CO £ ( 0 cul C0 ( 0 o *: O v. a. tor too > U L 2.5H 0.0 Idiopathic Infarction Data adapted from Gorelick et al. ( 5). FIG. 2. Comparison of the weighted vascular risk profile in the 10 patients with idiopathic downbeat nystagmus and nine patients with vasculopathic ( indicated by infarction) downbeat nystagmus. The median values, represented by the horizontal bar in each column, are not significantly different ( p = 0.24). / Neuro- Ophthalmol, Vol. 21, No. 1, 2001 DOWNBEAT NYSTAGMUS 41 The lack of statistical difference between the two groups for age and vascular risk factors supports the hypothesis that some idiopathic cases of DBN may be caused by strategically located and radiographically occult cerebral infarctions affecting the brainstem. Of course, our results should be tempered by the fact that the number of cases in the two groups was small, decreasing the overall power of our conclusions. On the other hand, despite the limitations imposed by a retrospective chart review, the variables we were interested in abstracting were universally present in all medical records of our patients, because each patient was specifically queried about the presence of these variables at the time they were initially evaluated. In summary, our pilot study suggests that the similar age and vascular risk profile of patients with idiopathic and vasculopathic DBN implicates a common mechanism of injury that might explain the cause of DBN in some patients whose work- up evaluation proves unre-vealing. We suggest a larger, and preferably prospective, study be performed to further test this hypothesis. A case- control design to compare vascular risk factors in each group with an unaffected population would enhance the validity of the conclusions. The use of pooled data from several sources would facilitate obtaining this data in a timelier manner. REFERENCES 1. Cogan DG. Down- beat nystagmus. Arch Ophthalmol 1968; 80: 757- 68. 2. Halmagyi GM, Rudge P, Gresty MA, et al. Downbeating nystagmus: a review of 62 cases. Arch Neurol 1983; 40: 777- 84. 3. Jacobson DM, Corbett JJ. Downbeat nystagmus associated with dolichoectasia of the vertebrobasilar artery. Arch Neurol 1989; 46: 1005- 8. 4. Yee RD. Downbeat nystagmus: characteristics and localization of lesions. Trans Am Ophthalmol Soc 1989; 87: 984- 1032. 5. Gorelick PB, Sacco RL, Smith DB, et al. Prevention of a first stroke. A review of guidelines and a multidisciplinary consensus statement from the national stroke association. JAMA 1999; 281: 1112- 9. J Neuro- Ophthalmol, Vol. 21, No. 1, 2001 |
