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Sensory (Touch)
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Download DOC: Sensory (Touch)
Caring For People With Huntington's Disease
Kansas University Medical Center
Editor: Edmond Chiu, AM
Chapter 5, Physiotherapy
Elizabeth Barraclough, Janet Hodge, Jill Groom, Anne Hoy
Assessment results indicate that some HD persons may experience disturbance of sensory function loss of discriminative ability.
Generally the ability to discriminate between the two remains intact. However, there are instances where:
(a) Sensation is dulled e.g., reduced ability to discriminate between, say, hot and very hot.
(b)It takes longer for the information to reach the cortex. The correct response may be given, but the test tube had to be held against the skin for several seconds longer than normal.
Two Point:
Discriminative ability is generally diminished and becomes more so as the disease progresses
Touch Localization
Particularly in latter stage sufferers the ability to localize touch is very poor.
Steroegnosis (the ability to recognize familiar objects by touch with vision occluded):
Overall this was within normal limits in the early stages of the disease. However, in the later stages problems with stereognosis were recognized, due either to reduced manipulative skills or the inability to put a name to the object, i.e., the problem was primarily a word finding difficulty.
Anesthesia and Pain Tolerance
Localized areas of anesthesia are not common, and are usually only found in persons with additional problems, e.g., stroke or alcoholism. However, staff at Arthur Preston Centre have noted high levels of pain tolerance in many residents. For instance, smokers can burn their fingers without complaining of pain. Similarly, patients have been known to lie on open sores with no apparent discomfort.
Sensation of effort is altered in Huntington's disease.
Lafargue G, Sirigu A.
Neuropsychologia. 2002;40(10):1654-61.
Institut des Sciences Cognitives, CNRS, 67 Boulevard Pinel, 69675 Bron, France.
These results suggest that effort sensation critically involves the basal ganglia. This signal and/or the integration of sensory feed-back which generates what is experienced as the sense of effort, would be altered in HD.
In this study, we investigated sensation of effort in Huntington disease (HD). We tested the hypothesis that the basal ganglia are involved in processing effort sensation.

The experimental paradigm consisted in a contralateral matching procedure where normal subjects (N=6) and HD patients (N=6) were required to lift a reference weight with their non-dominant index, and then compare the target-weight with variable weights lifted by the dominant index.

Two kinds of sequences were administered:
(1) increasing, where the first weight was lighter than the reference weight and progressively increased in 20g steps,
(2) decreasing, where trials started with a heavier weight and progressively decreased.
We calculated the discrimination threshold (DT) across sequences as the weight for which the subject's response changed
The difference between the higher and the lower threshold was defined as "uncertain area".
We predicted that controls should over-estimate the reference weight lifted by their non-dominant hand because the same effort produces more force when applied to stronger muscles.
If the basal ganglia mediates sensation of
effort, patients' capability to discriminate weights should be degraded.

As expected, normal subjects overestimated the reference weight lifted by their non-dominant index and showed a restricted uncertain area, thus, indicating that were able to discriminate minimal differences in generated forces.

By contrast, patients with HD under-estimated the reference weight lifted by their non-dominant hand and showed a broad uncertain area, thus, demonstrating that they could detect only important differences in the matched efforts.

These results suggest that effort sensation critically involves the basal ganglia. In normal conditions, in parallel with the efferent command of force, an efferent copy reflecting the magnitude of the voluntary motor command is transmitted to sensory centres.
This signal and/or the integration of sensory feedback which generates what is exper-ienced as the sense of effort, would be altered in HD.
Source: PubMed