Movement Disorders Vol. 5, No. 1, 1990, pp. 32-35 0 1990 Movement Disorder Society
Impaired Habituation of Long-Latency Stretch Reflexes of the Wrist Muscles in Huntington’s Disease G. Abbruzzese, D. Dall’Agata, M. Morena, *L. Spadavecchia, S. Ratto, and E. Favale Department of Neurology, University of Genoa, and *Institute of Cybernetics and Biophysics, C . N . R . , Genoa, Italy
Summary: Electromyographic responses to sudden wrist extension were recorded from the forearm and finger flexor muscles in 10 patients with Huntington’s disease (HD) and in 10 normal controls. Stretch reflexes were characterized by a short-latency (SL) and a long-latency (LL) component both in patients and controls. Latency, duration, and size of the S L component were not different in the two groups, whereas the LL component was delayed in latency and reduced in size in HD patients. Increasing the stretch repetition rate from 0.1 to 0.4 cyclesh did not affect the S L component of either group, whereas the LL stretch reflex was reduced in size and duration in normal controls, but not in HD patients. These findings suggest an impairment of the “gain” mechanisms of the sole LL component, responsible for a desaturation of this component. This study supports the hypothesis that L L stretch reflexes are mediated by a transcortical long loop, possibly damaged in HD. Key Words: Stretch reflexes-Habituation-Huntington’s disease-Long-loop mechanisms.
PATIENTS AND METHODS
Stretching of a contracting muscle produces a series of electromyographic (EMG) responses. The first, at “short latency” (SL), is generally regarded to be equivalent to the spinal monosynaptic reflex. After this early response, one or more “longlatency” (LL) components are observed, which also appear to be reflexive in nature, but the mechanisms underlying the latter responses are still controversial (for a review, see ref. 1). It has been reported recently (2,3) that the size of the stretch reflex components can be differently affected by the presentation rate, which may induce an habituation of the sole LL component, thus suggesting that SL and LL stretch reflexes are mediated by two different pathways. Indirect evidence (4-6) suggests that habituation of stretch reflexes may be abnormal in Huntington’s disease (HD). The present study was prompted to clarify this issue.
Ten patients, six women and four men, ages 3659 years, with clinically manifested HD were studied. The diagnoses were established on the basis of the clinical features and positive family histories of the disease. The main clinical features of the patients are summarized in Table l . Patients were evaluated according to the “chorea severity rating scale” (7). Ten age-matched normal volunteers served as controls. The stretch reflexes of the forearm and finger flexor (FF) muscles were studied while the subjects were seated comfortably in a chair with the forearm semipronated and strapped to a platform and the finger encased in a rigid splint. A potentiometer coaxial with the wrist joint monitored the angular position of the wrist, while angular velocity was obtained by analog differentiation of the position signal. EMG activity was recorded with Ag/AgCl surface electrodes applied 2-3 cm apart over the FF muscles and amplified (DISA 15C01, bandpass: 505,000 Hz, - 3 dB), full-wave rectified and inte-
~
Address correspondence and reprint requests to Dr. G. Abbruzzese, Clinica Neurologica dell’Universita’, Via De Toni 5, 1-16132 Genoa, Italy.
32
STRETCH REFLEX HABITUATION IN HUNTINGTON
33
TABLE 1. Clinical features of Huntington’s disease Case 1
2 3 4 5 6 7 8 9 10 Mean (SD)
Sex
F F M F F F F M M M
Age (yr)
Duration (Yd
41 55 44 43 36 59 43 54 53 49 47.7 (7.0)
4 12 10 3 2 2 5 1 4 4 4.7 (3.4)
Severity” 7 10 11 8 6 11 6 7 12
8 8.6 (2.1)
Muscle Tone -
> > < -
< -
<
Impaired Habituation of Long-Latency Stretch Reflexes of the Wrist Muscles in Huntington’s Disease G. Abbruzzese, D. Dall’Agata, M. Morena, *L. Spadavecchia, S. Ratto, and E. Favale Department of Neurology, University of Genoa, and *Institute of Cybernetics and Biophysics, C . N . R . , Genoa, Italy
Summary: Electromyographic responses to sudden wrist extension were recorded from the forearm and finger flexor muscles in 10 patients with Huntington’s disease (HD) and in 10 normal controls. Stretch reflexes were characterized by a short-latency (SL) and a long-latency (LL) component both in patients and controls. Latency, duration, and size of the S L component were not different in the two groups, whereas the LL component was delayed in latency and reduced in size in HD patients. Increasing the stretch repetition rate from 0.1 to 0.4 cyclesh did not affect the S L component of either group, whereas the LL stretch reflex was reduced in size and duration in normal controls, but not in HD patients. These findings suggest an impairment of the “gain” mechanisms of the sole LL component, responsible for a desaturation of this component. This study supports the hypothesis that L L stretch reflexes are mediated by a transcortical long loop, possibly damaged in HD. Key Words: Stretch reflexes-Habituation-Huntington’s disease-Long-loop mechanisms.
PATIENTS AND METHODS
Stretching of a contracting muscle produces a series of electromyographic (EMG) responses. The first, at “short latency” (SL), is generally regarded to be equivalent to the spinal monosynaptic reflex. After this early response, one or more “longlatency” (LL) components are observed, which also appear to be reflexive in nature, but the mechanisms underlying the latter responses are still controversial (for a review, see ref. 1). It has been reported recently (2,3) that the size of the stretch reflex components can be differently affected by the presentation rate, which may induce an habituation of the sole LL component, thus suggesting that SL and LL stretch reflexes are mediated by two different pathways. Indirect evidence (4-6) suggests that habituation of stretch reflexes may be abnormal in Huntington’s disease (HD). The present study was prompted to clarify this issue.
Ten patients, six women and four men, ages 3659 years, with clinically manifested HD were studied. The diagnoses were established on the basis of the clinical features and positive family histories of the disease. The main clinical features of the patients are summarized in Table l . Patients were evaluated according to the “chorea severity rating scale” (7). Ten age-matched normal volunteers served as controls. The stretch reflexes of the forearm and finger flexor (FF) muscles were studied while the subjects were seated comfortably in a chair with the forearm semipronated and strapped to a platform and the finger encased in a rigid splint. A potentiometer coaxial with the wrist joint monitored the angular position of the wrist, while angular velocity was obtained by analog differentiation of the position signal. EMG activity was recorded with Ag/AgCl surface electrodes applied 2-3 cm apart over the FF muscles and amplified (DISA 15C01, bandpass: 505,000 Hz, - 3 dB), full-wave rectified and inte-
~
Address correspondence and reprint requests to Dr. G. Abbruzzese, Clinica Neurologica dell’Universita’, Via De Toni 5, 1-16132 Genoa, Italy.
32
STRETCH REFLEX HABITUATION IN HUNTINGTON
33
TABLE 1. Clinical features of Huntington’s disease Case 1
2 3 4 5 6 7 8 9 10 Mean (SD)
Sex
F F M F F F F M M M
Age (yr)
Duration (Yd
41 55 44 43 36 59 43 54 53 49 47.7 (7.0)
4 12 10 3 2 2 5 1 4 4 4.7 (3.4)
Severity” 7 10 11 8 6 11 6 7 12
8 8.6 (2.1)
Muscle Tone -
> > < -
< -
<
