We thank our correspondent for his constructive comments.
In response to the first point raised: Downbeat nystagmus (DBN) or, better, the downbeat nystagmus syndrome, is usually accompanied by other oculomotor disturbances, especially gaze palsy (1) and saccadic pursuit, because the cerebellar flocculus is also important for the gaze holding function and pursuit. For this reason, the intensity of the DBN depends on the line of gaze.
In response to the second point raised: The most common provable causes of DBN are degenerative cerebellar disorders (2) as well as bilateral brain stem infarctions. All other causes mentioned are relatively rare, some have been described only in individual case reports.
In response to the third point raised: In addition to medication treatment, prism treatment is important and, in case none of the other procedures prove to be effective, even surgery is an option. Today’s medical drugs of choice for the treatment of DBN are the aminopyridines. These are effective even in type 2 episodic ataxia, as was shown by a recent placebo controlled study (3).
Footnotes
Conflict of interest statement
The authors of both contributions declare that no conflict of interest exists.
References
- 1.Glasauer S, Hoshi M, Kempermann U, Eggert T, Buttner U. Three-dimensional eye position and slow phase velocity in humans with downbeat nystagmus. J Neurophysiol. 2003;89:338–354. doi: 10.1152/jn.00297.2002. [DOI] [PubMed] [Google Scholar]
- 2.Wagner JN, Glaser M, Brandt T, Strupp M. Downbeat nystagmus: aetiology and comorbidity in 117 patients. J Neurol Neurosurg Psychiatry. 2008;79:672–677. doi: 10.1136/jnnp.2007.126284. [DOI] [PubMed] [Google Scholar]
- 3.Strupp M, Kalla R, Claassen C, et al. A randomized trial of 4-aminopyridine in EA2 and related familial episodic ataxias. Neurology. In press. 2011 doi: 10.1212/WNL.0b013e318225ab07. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Strupp M, Hüfner K, Sandmann R, et al. Central oculomotor disturbances and nystagmus: a window into the brainstem and cerebellum. Dtsch Arztebl Int. 2011;108(12):197–204. doi: 10.3238/arztebl.2011.0197. [DOI] [PMC free article] [PubMed] [Google Scholar]