Downbeat nystagmus (DBN) is the most frequent type of acquired nystagmus that is present in primary position (1,2). It impairs vision due to vertical oscillopsia (2–4) and frequently leads to postural instability (1–6). DBN is often caused by an identifiable cerebellar pathology, including cerebellar degeneration (7), which affects the flocculus bilaterally (8–10). It has been hypothesized that the bias drift of DBN is caused by a reduced function of the inhibitory, vertical gaze, velocity-sensitive Purkinje cells (PCs) in the cerebellar flocculus (9). Because these cells show a physiological asymmetry, having a preponderance of cells with downward on-directions, their loss leads to disinhibition of neurons in the superior vestibular nucleus and the adjacent Y group and, hence, to spontaneous upward drift (11–13). In primary gaze, this upward drift leads to fast phases that are downward (4,14). This upward-directed drift generally increases in downgaze and decreases or even reverses in upgaze.
Clinical studies have shown that aminopyridines improve DBN (2,6,15–17). In patients with episodic ataxia type 2, aminopyridines also reduces interictal cerebellar ataxia (18) and the frequency of attacks (19). In addition, 3,4-DAP has been used in Lambert-Eaton myasthenic syndrome and 4-AP (in the sustained release form, Ampyra; Biogen Idec, Cambridge, MA) for gait impairment in multiple sclerosis (20–27).
Aminopyridines increase the resting activity and excitability of the PCs, which may restore their inhibitory influence on deep cerebellar nuclei and vestibular nuclei (28). It has also been demonstrated that therapeutic concentrations of 4-aminopyridine restore the diminished precision of pacemaking in PCs of the ataxic P/Q channel mutant mouse by prolonging the action potential and increasing the action potential after hyperpolarization (29). The effects of 4-AP on the cerebellum were confirmed by a positron emission tomographic study that showed that 4-AP increased metabolic activity bilaterally in the cerebellar flocculus (20).
We conducted a double-blind, crossover study to look at the effects of single doses (10 mg) of 4-AP or 3,4-DAP on the mean slow-phase velocity (SPV) in 8 patients with DBN prior to, 45 minutes after, and 90 minutes after administration. Obtaining our first measurement 45 minutes following the oral administration of the drugs was chosen because prior studies in patients with multiple sclerosis have shown that both drugs are rapidly absorbed with peak serum levels ranging from 20 to 60 minutes after dosing (21). We chose 90 minutes as our second measurement because serum half-life was reported to lie between 1 and 3 hours (21).
Eight patients with DBN were included in our study (Table 1). Mean duration of DBN was 7.8 years (range, 3–24 years) and patient age ranged from 58 to 76 years (mean, 68 ± 5.93 years). Patients were randomly assigned capsules of 10 mg of 3,4-DAP or 4-AP; they received 1 single capsule of either substance. There was a washout period of 6 days when no medication was given. One week later, the treatment was switched (i.e., they received a single capsule of the other substance). On both days of testing, the patients' eye movements were recorded prior to the administration of medication and 45 minutes and 90 minutes later. In the intervals between the recordings, patients rested in an upright position.
As in our previous studies (14), all patients underwent a complete clinical examination, including neuro-ophthalmological, neuro-otological, and neurological tests, high-resolution MRI of the brainstem and the cerebellum, electronystagmography with caloric irrigation, electrocardiography, and hematological tests, including vitamin B12 and magnesium levels. No patient was taking medication that affected the vestibular or ocular motor systems, and DBN was not caused by medication or a metabolic disorder. All patients gave informed consent, and the study was performed in accordance with the Helsinki II Declaration and was approved by the Ethics Committee of the Ludwig-Maximilians University Medical Faculty.
Recording of Eye Movements
During the 3 measurement sessions (before medication, 45 minutes and 90 minutes after medication), patients were monitored in an upright position. A 30-second eye movement recording was made with 3-dimensional video-oculography (GN Otometrics Hortmann Vestlab 100 (GN Store Nord, Ballerup, Denmark), with a 50 Hz sampling rate, 0.1° resolution in horizontal and vertical directions, accuracy of 0.6°, a range of ±30° in the horizontal and vertical directions) (14,23). It took place in the following order (calibration in 8.5° position): 1) gaze straight ahead with fixation turned on; 2) gaze straight ahead in darkness (with no possibility to fixate on a fixation point); 3) 17° rightward gaze; 4) 17° leftward gaze; 5) 17° upward gaze; and 6) 17° downward gaze. The target was projected by laser onto a white background placed 60 cm in front of the patient. For every recording, the chair and head restriction were adjusted so that the target appeared at eye level and the head was fixed in position.
Monitoring of Side Effects
Before providing their informed consent, all patients had received information about possible medication side effects. They were asked immediately, 30 minutes, 1 hour, and 2 hours after taking the medication whether they were experiencing any side effects.
Data Acquisition and Calibration
Eye position was measured with 3-dimensional video-oculography (23) for 30 seconds. Data were analyzed off-line using Matlab (Mathworks, Natick, MA). The calibrated data were low-pass filtered applying a digital Gaussian filter with a bandwidth of 30 Hz, smoothing out higher-frequency components above 30 Hz in the eye position data. The calculated filter coefficients were convolved with the eye position data in Matlab software (Mathworks). Eye velocity was calculated from this smoothed signal by numerical differentiation. Saccades were detected automatically by the software program and manually checked by a trained technician. This was particularly important in patients with a high frequency of saccades. Possible detection errors were corrected manually, and the mean SPV was computed from this data.
Statistical Data Analysis
Repeated measurement analysis of variances (Statistica 6.1; Statsoft, Tulsa OK) were carried out along with post hoc Scheffé tests for individual comparisons. SPV of vertical eye movements was the dependent variable. The values of all the following figures were transformed so that DBN indicated by SPV degrees/second (°/s) appears as a negative value on the scale, whereas the absence of DBN appears as a (close to) zero value. The analysis included the following: fixation (=light on) vs viewing in the dark (=light off), medication type (4-AP vs 3,4-DAP), and time (before medication, 45 minutes after medication, 90 minutes after medication).
Both medications had a salutary effect on DBN. Representative eye movement recordings are illustrated in Figure 1. The analysis of variance included a comparison between both medications over time (pre vs post 45 minutes vs post 90 minutes). This analysis was significant (P < 0.01) with the F test reaching a value of 8.88 (numerator degrees of freedom = 2, denominator degrees of freedom = 14).
Following the administration of 3,4-DAP, mean SPV decreased from −5.68°/s (pre) to −3.29°/s (post 45) to −2.96°/s (post 90) (with Scheffé post hoc comparisons between pre and post 45/post 90; P < 0.01). Following the administration of 4-AP, mean SPV decreased from −6.04°/s (pre) to −1.58°/s (post 45) to −1.21°/s (post 90) (with Scheffé post hoc comparisons between pre and post 45; P < 0.00001, and between pre and post 90; P < 0.00001). While the pre-mean SPV measurements of both medications did not significantly differ from each other (−6.04°/s vs −5.68°/s; P = 0.97), both post 45 and post 90 SPV measurements were significantly lower for 4-AP than for 3,4-DAP (–1.58°/s vs −3.29°/s and –1.21°/s vs –2.96°/s with each Scheffé test; P < 0.05) (Fig. 2).
All patients apart from Cases 2 and 5 responded with a mean SPV decline after the administration of 3,4-DAP. After the administration of 4-AP, Case 2 again did not respond with a decline in mean SPV, while Case 5 showed a reverse from negative mean SPV values (DBN) to positive values (indicating upbeat nystagmus).
Additional significant findings included the effect of time for both medications: pre vs post 45 vs post 90 (F(1,7) = 10.72; P < 0.01); individual Scheffé tests between pre and post 45 (P < 0.01), between pre and post 90 (P < 0.01), and between post 45 and post 90 (P > 0.05). DBN also had a lower mean SPV in light (F(1,7) = 14.14; P < 0.01). Fixation on the target (=light on) was associated with an average SPV value of –2.23°/s. No fixation (=light off) was associated with an average SPV value of −4.69°/s.
All 8 patients reported mild paresthesias from 30 minutes to 2 hours after ingestion of both medications. No other side effects were reported.
It had been previously shown that both 4-AP and 3,4-DAP decrease the mean SPV of DBN (2,21,23–25). It was unclear whether they differ in terms of their treatment efficacy. Therefore, identical single 10-mg doses of both aminopyridines were compared in our double-blind study with crossover design. Our results demonstrate that 4-AP decreased the intensity of DBN significantly more than did 3,4-DAP. This may be due to the different pharmacokinetics and the action of the 2 aminopyridines in blocking cellular potassium channels. Would these results be different if we had observed the effects of 3,4-DAP and 4-AP over a longer period of time? We do not expect a different outcome because both medications reach their peak serum level approximately 60 minutes after oral administration (21). There are conflicting reports that the 2 drugs may have similar half-lives (21) or that 4-AP has a longer half-life than 3,4-DAP (26,27,30,31). In addition, 4-AP has a better ability to cross the blood-brain barrier because it is highly lipid soluble and able to block K+ channels in both the central and peripheral nervous systems (21,26,27,30–32). 3,4-DAP is only soluble in aqueous solution and does not cross the blood-brain barrier easily. It acts primarily to block K+ channels in the peripheral nervous system (23). Given that DBN is a central ocular motor disorder, one would expect 4-AP to have a greater effect on DBN.
With the exception of paresthesias, none of our patients experienced side effects after ingestion of either medication. There were similar complaints following the administration of both medications. This is consistent with previous studies (2,15–17,21,33–35). Not all patients may be eligible for aminopyridines due to prolonged frequency-corrected QT intervals in the electrocardiogram, where potassium-blocking drugs, such as aminopyridines, could lead to dangerous cardiac arrhythmias. As an alternative, one might want to consider behavioral approaches to reduce DBN, for example, to rest in upright head position (36).
Our study was limited in that we only assessed mean SPV as a measure of improvement in DBN. For future studies, it will be important to look at other parameters, including visual acuity, nystagmus amplitude, and nystagmus frequency.
The authors thank Judy Benson for proofreading the manuscript and all patients for taking part in the study. They also thank Dr Rainer Spiegel and Dr Stefan Glasauer who carried out the statistical analyses and Dr Erich Schneider and by Dr Ales Hahn for providing additional technical and statistical advice (with an emphasis on the 3D video-oculographic device).
1. Baloh RW, Spooner DW. Downbeat nystagmus: a type of central vestibular nystagmus. Neurology. 1981;31:304–310
2. Kalla R, Glasauer S, Büttner U, Brandt T, Strupp M. 4-aminopyridine restores vertical and horizontal neural integrator function in downbeat nystagmus. Brain. 2007;130:2441–2451
3. Bronstein AM. Vision and vertigo: some visual aspects of vestibular disorders. J Neurol. 2004;251:381–387
4. Leigh RJ, Zee DS The Neurology of Eye Movements, 4th edition. 2006 New York, NY Oxford University Press
5. Pierrot-Deseilligny C, Milea D. Vertical nystagmus: clinical facts and hypotheses. Brain. 2005;128:1237–1246
6. Sprenger A, Zils E, Rambold H, Sander T, Helmchen C. Effect of 3,4-diaminopyridine on the postural control in patients with downbeat nystagmus. Ann N Y Acad Sci. 2005;1039:395–403
7. Wagner JN, Glaser M, Brandt T, Strupp M. Downbeat nystagmus: aetiology and comorbidity in 117 patients. J Neurol Neurosurg Psychiatry. 2008;79:672–677
8. Hüfner K, Stephan T, Kalla R, Deutschländer A, Wagner J, Holtmannspötter M, Schulte-Altedorneburg G, Strupp M, Brandt T, Glasauer S. Structural and functional MRIs disclose cerebellar pathologies in idiopathic downbeat nystagmus. Neurology. 2007;69:1128–1135
9. Kalla R, Deutschländer A, Hüfner K, Stephan T, Jahn K, Glasauer S, Brandt T, Strupp M. Detection of floccular hypometabolism in downbeat nystagmus by fMRI. Neurology. 2006;66:281–283
10. Zee DS, Yamazaki A, Butler PH, Gücer G. Effects of ablation of flocculus and paraflocculus of eye movements in primate. J Neurophysiol. 1981;46:878–899
11. Marti S, Straumann D, Büttner U, Glasauer S. A model-based theory on the origin of downbeat nystagmus. Exp Brain Res. 2008;188:613–631
12. Averbuch-Heller L, Tusa RJ, Fuhry L, Rottach KG, Ganser GL, Heide W, Büttner U, Leigh RJ. A double-blind controlled study of gabapentin and baclofen as treatment for acquired nystagmus. Ann Neurol. 1997;41:818–825
13. Dieterich M, Straube A, Brandt T, Paulus W, Büttner U. The effects of baclofen and cholinergic drugs on upbeat and downbeat nystagmus. J Neurol Neurosurg Psychiatry. 1991;54:627–632
14. Spiegel R, Rettinger N, Kalla R, Lehnen N, Straumann D, Brandt T, Glasauer S, Strupp M. The intensity of downbeat nystagmus during daytime. Ann N Y Acad Sci. 2009;1164:293–299
15. Strupp M, Schüler O, Krafczyk S, Jahn K, Schautzer F, Büttner U, Brandt T. Treatment of downbeat nystagmus with 3,4-diaminopyridine—a placebo-controlled study. Neurology. 2003;61:165–170
16. Helmchen C, Sprenger A, Rambold H, Sander T, Kömpf D, Straumann D. Effect of 3,4-diaminopyridine on the gravity dependence of ocular drift in downbeat nystagmus. Neurology. 2004;63:752–753
17. Kalla R, Glasauer S, Schautzer F, Lehnen N, Büttner U, Strupp M, Brandt T. 4-aminopyridine improves downbeat nystagmus, smooth pursuit, and VOR gain. Neurology. 2004;62:1228–1229
18. Löhle M, Schrempf W, Wolz M, Reichmann H, Storch A. Potassium channel blocker 4-aminopyridine is effective in interictal cerebellar symptoms in episodic ataxia type 2-A video case report. Mov Disord. 2008;23:1314–1316
19. Strupp M, Kalla R, Dichgans M, Freilinger T, Glasauer S, Brandt T. Treatment of episodic ataxia type 2 with the potassium channel blocker 4-aminopyridine. Neurology. 2004;62:1623–1625
20. Bense S, Best C, Buchholz HG, Wiener V, Schreckenberger M, Bartenstein P, Dieterich M. 18F-fluorodeoxyglucose hypometabolism in cerebellar tonsil and flocculus in downbeat nystagmus. Neuroreport. 2006;17:599–603
21. Judge SI, Bever CT Jr. Potassium channel blockers in multiple sclerosis: Neuronal Kv
channels and effects of symptomatic treatment. Pharmacol Ther. 2006;111:224–259
22. Halmagyi GM, Curthoys IS. Clinical sign of canal paresis. Arch Neurol. 1988;45:737–739
23. Zingler VC, Kryvoshey D, Schneider E, Glasauer S, Brandt T, Strupp M. A clinical test of otolith function: static ocular counterroll with passive head tilt. Neuroreport. 2006;17:611–615
24. Kalla R, Spiegel R, Wagner J, Rettinger N, Jahn K, Strupp M. Pharmacotherapy of central oculomotor disorders. Nervenarzt. 2008;79:1377–1385
25. Sprenger A, Rambold H, Sander T, Marti S, Weber K, Straumann D, Helmchen C. Treatment of the gravity dependence of downbeat nystagmus with 3,4-diaminopyridine. Neurology. 2006;67:905–907
26. Leigh RJ. Potassium channels, the cerebellum, and treatment for downbeat nystagmus. Neurology. 2003;61:158–159
27. Bever CT. The current status of studies of aminopyridines in patients with multiple sclerosis. Ann Neurol. 1994;36:S118–S121
28. Etzion Y, Grossman Y. Highly 4 aminopyridine sensitive delayed rectifier current modulates the excitability of guinea pig cerebellar Purkinje cells. Exp Brain Res. 2001;139:419–425
29. Alviña K, Khodakhah K. The therapeutic mode of action of 4-aminopyridine in cerebellar ataxia. J Neurosci. 2010;30:7258–7268
30. Hayes KC, Katz MA, Devane JG, Hsieh JT, Wolfe DL, Potter PJ, Blight AR. Pharmacokinetics of an immediate-release oral formulation of Fampridine (4-aminopyridine) in normal subjects and patients with spinal cord injury. J Clin Pharmacol. 2003;43:379–385
31. Kalla R, Spiegel R, Rettinger N, Glasauer S, Strupp M. Therapy of downbeat nystagmus: 4-aminopyridine versus 3,4-diaminopyridine. Klinische Neurophysiologie. 2009;40:69
32. Lemeignan M, Millart H, Lamiable D, Molgo J, Lechat P. Evaluation of 4-aminopyridine and 3,4-diaminopyridine penetrability into cerebrospinal fluid in anesthetized rats. Brain Res. 1984;304:166–169
33. Jones RE, Heron JR, Foster DH, Sneglar RS, Mason RJ. Effects of 4-aminopyridine in patients with multiple sclerosis. J Neurol Sci. 1983;60:353–362
34. Stefoski D, Davis FA, Faut M, Schauf CL. 4-Aminopyridine improves clinical signs in multiple sclerosis. Ann Neurol. 1987;21:71–77
35. Davis FA, Stefoski D, Rush J. Orally administered 4-aminopyridine improves clinical signs in multiple sclerosis. Ann Neurol. 1990;27:186–192
36. Spiegel R, Kalla R, Rettinger N, Schneider E, Straumann D, Marti S, Glasauer S, Brandt T, Strupp M. Head position during resting modifies spontaneous daytime decrease of downbeat nystagmus. Neurology. 2010;75:1928–1932