Visual electrophysiology in Parkinson's disease: relation to clinical and functional impairments

Degenerative changes in Parkinson's disease [PD] may cause visual problems that may interfere with the quality of life. Special tests measuring electrical activity in the eye and the brain such as visual evoked potentials [VEP] and electroretinogram [ERG] have shown abnormalities in PD patients. It is not clear whether these visual abnormalities are the result of degeneration in the brain or whether some may be due to lowered dopamine levels in the retina. The interest in visual deficits in PD is enhanced by the possible relation between vision and control of balance. The aim of this work was to assess visual electrophysiological abnormalities in PD patients and their relation to clinical and functional [postural] impairments. The study included ten parkinsonian patients and ten apparently healthy control subjects. Assessment of disease severity was conducted using the Hoehn Yaher scale. Visual electrophysiological studies included pattern reversal VEP and ERG. The ability to effectively use visual information to control balance was assessed using sensory organization test [SOT]. Compared to the control group, PD patients had significantly prolonged VEP latencies mainly for bilateral full field and temporal halves of the retina. VEP amplitude was significantly increased for binocular stimulation. Flash ERG showed significantly low b-wave amplitude. Performance on SOT revealed the presence of significantly low visual ratio and visual preference ratio. Electrophysiological abnormalities were not correlated with clinical manifestations. VEP amplitudes were found to correlate with some ERG parameters. SOT findings were not found to correlate with electrophysiological abnormalities. Disturbed visual function as evidenced by visual electrophysiological abnormalities seems to be an inherent property in PD. Contribution of visual dysfunction to balance problem in these patients is evident. The mechanism by which visual disturbance contributes to balance disorders seems to differ from that responsible for VEP and ERG abnormalities signifying the important role played by dopamine in mediating different visual functions through different pathways

Proprioception and stabilizing reactions of the quadriceps and hamstrings in knee osteoarthitis

Knee joint proprioception has been shown to be deficient in patients with knee osteoarthritis. This might be the outcome of the operating pathology. Proprioceptive-mediated postural evoked responses of the quadriceps and hamstring muscles may be affected by the deficient proprioception. Such impairment may have a deleterious effect on the joint integrity as these muscular responses are protective for the joint during loading. To evaluate the proprioceptive-mediated stabilizing quadriceps and hamstring muscles activity posturally evoked by support surface perturbation in patients with knee osteoarthritis. The postural-evoked response surface EMG [SEMG] of the quadriceps and hamstrings following downward perturbation of the support surface were studied in 40 patients with knee osteoarthritis and compared to 20 matching healthy control subjects. In addition, knee joint proprioception was assessed by measuring inaccuracy of reproducing target 10, 20 and 30 degrees active flexion angel while standing. Postural stability was assessed by recording parameters of the center of pressure [COP] of single legged stance using a force platform. Patients showed significantly larger SEMG normalized response amplitude [mean, for right and left 0.9517 +/- 0.45222 and 0.9411 +/- 0.40585] compared to control [0.3524 +/- 0.1408 and 0.4777 +/- 0.2663, for right and left side respectively] [Z=-3.994 and -3.035, p=0.000 and 0.002]. Patients showed significantly delayed peak latency of hamstring activation [patients mean 175.04 +/- 63.03 ms and 197, 27 +/- 59.9 ms, control mean 133.50 +/- 32.67 and 135.50 +/- 33.62, for the right and left sides respectively] [Z=-1.966 and -2.666, p=0.049 and 0.008]. In addition, significant asymmetry of activation latency and amplitude were observed in patients compared to control regarding the quadriceps and hamstring bilateral responses. Patients showed significant proprioception inaccuracy with 30 degree active knee flexion reproduction [percent proprioception inaccuracy at 30[o] target angle for patients = 12.85 +/- 10.34, control= 3.55 +/- 5.25; Z=-2.443, p=0.015]. A set of significant correlations has been found between SEMG variables and each of the COP parameters, knee joint proprioception inaccuracy as well as pain score on visual analogue scale. Abnormalities of postural-evoked quadriceps and hamstring responses were found in patients with knee osteoarthritis. Direct and indirect relationship could be emphasized between these variables and deficient knee joint proprioception. The results support the assumption that previously reported deficiency of knee joint proprioception has a significant effect on the postural-evoked responses of the quadriceps and hamstrings in patients with knee osteoarthritis. Accordingly, improvement of thigh muscles proprioceptive-mediated postural activity could be a valuable component of the rehabilitation exercises designed for those patients

Partial body weight-supported treadmill training for gait restoration in hemiplegic patients: evaluation of using motor evoked potentials

Partial body weight support treadmill training [PBWST] is a task-oriented gait rehabilitation protocol for hemiplegic/paretic patients with proven clinical efficiency. At the neurophysiologic level, motor-evoked potentials [MEP] induced by transcranial magnetic stimulation [TMS] and recorded from target lower limb muscles may be used to assess the post-rehabilitation effects. Assessment of the effects of PBWST on the MEPs recorded from target lower limb muscles in chronic post-stroke hemiparetics. Thirty patients with post-stroke chronic hemiparesis were randomly allocated to one of 2 groups; PBWST group and conventional rehabilitation group. Initial evaluation included recording the MEP parameters from the quadriceps, tibialis anterior and gastrocnemius muscles. In addition, functional assessment tools included Fugel-Meyer assessment [FMA], functional ambulation category as well as Standing Balance Test. Endpoint evaluation using the same methods were obtained by the completion of 8 weeks of rehabilitation at a frequency of 3 times a week. Both study groups have shown significant post rehabilitation improvement of most of the recorded MEP parameters. The magnitude of post-rehabilitation change in the PBWST group was generally larger than in the other group. Significant correlation was observed between some parameters of the MEPs and the isolated movement subset of the FMA of both groups. Post-rehabilitation tibialis anterior latency was a significant predictor of post-rehabilitation co-ordination subset of the FMA in PBWST group. Pre- and post-rehabilitation latency and amplitude of the quadriceps MEP were significant predictor of the co-ordination subset of the FMA in the conventional rehabilitation group. MEPs parameters can monitor rehabilitation effects of PBWST at the neurophysiological level. The magnitude of PBWST post-rehabilitation effects was generally higher. MEP parameters can be used as predictors of functional outcome