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Cerebellar dyssynergia in humans.

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LETTERS
Cerebellar D y ssy nergia
in Humans
Ronald W. Angel, M D
The recent article by Miller and Freund, Cerebellar dyssynergia in humans-a quantitative analysis (Ann Neurol
8:574-579, 1980), describes an interesting and potentially
valuable method for studying patients with dyssynergia.
Two points deserve comment.
In the Fourier-analyzed power spectrum, the relative
amplitude of the second harmonic, expressed as a percentage of the amplitude corresponding to the fundamental
(input) frequency, was found to be significantly greater in
the dyssynergic group than in normal subjects (p < 0.05).
However, this measure was also greater for the clinically
unaffected hand in patients with a unilateral cerebellar syndrome ( p < 0.005). Thus, thep value for the four clinically
unaffected hands was actually more impressive than that for
the nine dyssynergic hands.
The table indicates that, in normal persons, the mean size
of the second harmonic was 2.14% of the amplitude corresponding to the input frequency. In seven limbs with mild
to moderate dyssynergia the value was 14.9%; in the clinically unaffected hands of four patients with unilateral disease it was 15.09%. If this percentage is taken as a measure
of dyssynergia, one must ask: why was this measure almost
the same in the clinically unaffected limbs and in limbs with
mild to moderate dyssynergia?
A second point concerns the labeling of the abscissa in
Figure 2, which reads “Power Spectrum-Log Frequency
(Hz).” Although the frequencies are displayed on a logarithmic scale, it is clear from the text that each point on
the x-axis stands for a frequency, not the logarithm of a
frequency. If the labeling were correct, then the number
5.0 would stand for the logarithm of the indicated frequency and the frequency would be 10,000. Since the
graph covers only the range up to 5.0 Hz, the correct
labeling for the x-axis would appear to be “Power
Spectrum-Frequency (Hz).”
Department of Neurology
Veterans Administration Medical Center
and Stanford University School of Medicine
3801 Miranda hve
Palo Alto, C h 94304
Reply
Robert G. Miller, MD,” and Hans-J. Freund, M D t
We thank Dr Angel for his incisive comments about our
study of cerebellar dyssynergia. H e is quite correct about
the labeling in Figure 2.
The major point requiring explanation is the increased
amplitude of the second harmonic in the clinically unaffected hand of four patients with a unilateral cerebellar
syndrome. We can only speculate about the basis of this
finding as follows. Standard clinical tests of cerebellar
function were used to determine whether a hand was clini-
202
cally unaffected. These tests involve muscles that are more
proximal and perform less precise movements than those
examined in the visual tracking test (finger flexors and extensors). In addition, the sensitivity of the visual tracking
test may be greater than that of the clinical examination.
These factors may explain the presence of increased
amplitude of the second harmonic in “clinically unaffected
hands.”
That a rough correlation exists between harmonic distortion and clinical rating of dyssynergia is seen in Figure 6
of our paper. However, there is considerable variability
among subjects, which is magnified by comparing, for
example, the four with moderate dyssynergia (second harmonic amplitudes of 1.60, 2.72, 11.4, and 40.8%). The
same variability exists among the four subjects with clinically unaffected hands (second harmonic of 3.46, 11.7,
12.2, and 33.0%). In this very small sample it appears unlikely that the degree of harmonic distortion has much
bearing. The important point in our opinion is the detection of harmonic distortion in limbs contralateral to a focal
cerebellar lesion. The two subjects with greatest harmonic
distortion had a discrete tumor in the cerebellar hemisphere on the opposite side. Although this observation
seems to contradict classic neurophysiological principles,
the same observation has recently been made by Gilman
and associates [l].
+NeuromuscularResearch Unit
Children’s Hospital of San Francisco
San Francisco, CA 941 19
tNeurologische Universitats Klinik
Dusseldorf, West Germany
Reference
1. Gilrnan S, Bloedel JR, Lechtenberg R. Disorders of the Cerebellum (Contemporary Neurology Series, Vol 2 1). Philadel-
phia, Davis, 1981
Prediction of
Huntington’s Disease
C. D. Marsden, MB, MSc, FRCP, MRCPsych
Klawans et a1 [2] gave an excellent review of the various
attempts made to produce a predictive test for the Huntington’s disease gene in those at risk of developing the
illness, but did not discuss when or if such a test should be
used. Children and siblings of persons with Huntington’s
disease commonly and correctly request such a test as they
approach adult life, so as to plan their own reproduction
appropriately. At present, no such proved reliable test
exists, so those at risk cannot be provided with the information they seek.
What will the consequences be when such an established
test does become available? In essence, since there is yet no
cure for Huntington’s disease, those with a positive result
will face a protracted certain death sentence, although
those fortunate enough to prove negative will have the
cloud of uncertainty lifted (assuming that such a test is in-
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