Periodicity in the Hoffmann reflex recovery curve

Soleus H-reflex measures in patients with focal and generalized dystonia

OBJECTIVE

The purpose of this study was to examine neurophysiological characteristics of dystonia patients using electromyographic soleus H-reflex methods.

METHODS

Thirty normal healthy individuals were compared to 27 patients with focal (cervical) or generalized dystonia. Three H-reflex assessment methods were included: the ratio of maximum H-reflex to direct muscle potential (H/M ratio); vibration inhibition (H(v)/H(c) ratio); and H-reflex recovery curves (HRRC).

RESULTS

Average H/M ratios between groups were not statistically significant. The average H(v)/H(c) ratio for the generalized dystonia group was significantly greater than the focal dystonia and normal groups. Average values of the HRRC showed the generalized dystonia group had significantly greater disinhibition than the focal dystonia and control groups during the early inhibition phase. The HRRC for the focal dystonia group was greater than normal and more similar to the generalized dystonia group during the late phases of the recovery curve. The average value of the localized late facilitation phase for the focal dystonia group was significantly greater than the control group and less than the generalized dystonia group. No differences were observed between groups for the average localized late inhibition phase of the recovery curve.

CONCLUSIONS

Soleus H-reflex measures identified neurophysiologic differences between generalized dystonia, cervical dystonia and normal conditions.

SIGNIFICANCE

This methodology enables analysis of the underlying characteristics of dystonic pathologies using soleus H-reflex methods rather than upper extremity H-reflex techniques.

H-reflex recovery curves differentiate essential tremor, Parkinson's disease, and the combination of essential tremor and Parkinson's disease

The purpose of this study was to examine H-reflex parameters among the pathophysiologic conditions of essential tremor (ET), Parkinson's disease (PD), combined essential tremor with Parkinson's disease (ETPD), and a control group. H-reflex latencies, amplitude of maximum H-reflex to maximum M-response ratio (H:M), vibration H-reflex to control H-reflex (Hv:Hc), and H-reflex recovery curves (HRRCs) were recorded and compared between a control group and patient groups with ET, early-stage PD, and with ETPD. No statistically or clinically significant differences were found between the patient groups and the control group for latency, H:M ratio, or Hv:Hc ratio. Significantly greater ratio values were observed for the PD group over the other groups for the HRRC tests at each interstimulus interval between 200 and 300 msec (p < 0.05), but values were not different between PD and ETPD patients for intervals between 350 and 1,000 msec. Patients with ET, PD, and ETPD apparently have different underlying pathologies. HRRC tests do not distinguish ET patients from normal, but differentiates specifically between PD and ETPD, and normal individuals. HRRC testing may be a useful method for evaluating pathologies between ET, PD, and ETPD patients.

Methods of H-reflex evaluation in the early stages of Parkinson's disease

Differentiating the early stages of Parkinson's disease from the normal consequences of aging or from other common neurologic conditions can be diagnostically problematic. The purpose of this study was to compare methodologies for measuring motor neuron excitability of Parkinson's disease patients with a control group. H-reflexes were monitored in 16 patients diagnosed in the early stages of Parkinson's disease (Hoehn & Yahr stages I and II) compared with 30 subjects who were disease free. Methods of measurement included H-reflex latencies, the relative values of maximum H-reflexes to maximum direct motor responses (H-to-M ratio), the relative values of H-reflex amplitudes during vibration compared with control H-reflex amplitudes (Hv-to-Hc ratio), and double-stimulation H-reflex recovery curves using different interstimulus interval parameters. No significant differences were observed for the H-to-M or Hv-to-Hc ratios, or for the H-reflex latencies. The H-reflex recovery curves for the patients with Parkinson's disease demonstrated significantly greater ratio amplitudes than the control group during the double-stimulus responses between the 150-msec and 700-msec interstimulus intervals. Although comparisons of simple H-reflexes and H-reflexes during vibration did not differentiate the patients in the early stages of Parkinson's disease from the control group, the double-stimulation paradigm was a sensitive method for detecting early diagnoses of this disease.

Evidence of a contralateral motor influence on reciprocal inhibition in man

The role of contralateral movement on both H reflex and reciprocal inhibition was studied. In normal men H reflex was induced by median nerve stimulation. Reciprocal inhibition was achieved through stimulation of the antagonist radial nerve. On this basis the effects of contralateral arm movement were analyzed. Furthermore the putative influence of exteroceptive origin was also verified by means of digit stimulation. Results showed that contralateral arm movement did not affect H reflex amplitude; on the contrary, it was able to enhance reciprocal inhibition induced by extensors on flexors. Study of cutaneous afferents demonstrated that contralateral digit stimulation failed to elicit modifications on both H reflex and reciprocal inhibition. On the other hand, ipsilateral digit stimulation lowered H reflex amplitude and increased the degree of reciprocal inhibition. Experimental findings underline the possibility that an informational array reaches the contralateral IA interneuron: therefore a mutual (bilateral) interaction among IA interneurones may accordingly be hypothesised.