We have not been impressed with sensitivity of cVEMPs to central disorders such as brainstem strokes. The difficulty seems to be that the latencies in cVEMPs (at least with tone bursts), are so variable that there is inadequate sensitivity to disease. This may be an artifact of our methodology (tone burst), which is temporally a longer stimulus than a click. We don't have any examples to show here, so we will just mention what is in the literature.
cVEMPs are often asymmetrical in spasmodic torticollis (Colebatch, Di Lazzaro et al. 1995).
cVEMP's are reduced in progressive supranuclear palsy (PSP), according to Liao et al (2008). PSP is a rare degenerative disorder of the CNS that generally results in death within 5 years of diagnosis. The average VEMP amplitude was reported to be 54, with a range of 16.8 to 214. This range overlapped substantially with age-matched controls, but may be another helpful method of identifying PSP. No data is presently available concerning progression of VEMP's in PSP patients over time. One would expect a decline. These patients are unusual however and a longitudinal study would not be easy to carry out.
cVEMPS, like other evoked potential tests, can also be abnormal in central diseases such as multiple sclerosis (MS). (Shimizu, Murofushi et al. 2000; Versino, Colnaghi et al. 2002; Murofuschi et al, 2001) and brainstem stroke (Chen et al. 2003). VEMPs test mainly measure lower brainstem function (medulla), while the ABR also tests upper brainstem function (medulla pons and midbrain). Here, latency measures would seem more logical than amplitude measures.
|Normal VEMP in patient with Machado-Joseph disease (Sca-3). The amplitude is low (30-50) but the latency is normal in this middle aged individual with genetically proven sca3 for 5 years, with gait ataxia, a small brainstem, and bilateral upgoing toes.|
cVEMP's are reported abnormal in certain cerebellar degenerations (i.e. Machado Joseph disease), but normal in others (e.g. OPCA, cortical cerebellar degeneration). (Tagegoshi and Murofushi, 2000). As VEMP circuitry is not thought to involve the cerebellum, it would be surprising to find abnormal VEMP's in any purely cerebellar condition. In our own practice (see above), but we have only studied two patients and found abnormally reduced amplitude for age in one and an absent VEMP in the other. As Machado-Joseph affects the brainstem, the mechanism for the reduced VEMP may lie in damage to other locations than the cerebellum.