Excitatory and inhibitory corticospinal responses to transcranial magnetic stimulation in patients with minor to moderate head injury

OBJECTIVES—The changes in excitatory and inhibitory responses to transcranial magnetic stimulation (TMS), as attested by motor evoked potential (MEP) and silent period (SP) parameters, were compared in patients who sustained minor to moderate head injury.
METHODS—A total of 38 patients with brain concussion, and diffuse, focal, and combined brain injury and 20 healthy volunteers were examined. The MEPs and SPs were recorded from the abductor pollicis brevis muscle after single pulse TMS 2 weeks after head trauma. The parameters assessed were the MEP resting threshold, the MEP/M wave amplitude ratio, the central motor conduction time (CMCT), the SP threshold, the interthreshold difference (ITD), and the SP duration (SPD).
RESULTS—The main finding was an increase in the ITD in patients with mild and moderate head injury due to the relatively greater augmentation of the MEP threshold. This was associated with a reduction of the MEP/M wave amplitude ratio. The degree of MEP and SP changes depended on severity of head injury and was not related to the type of brain lesions. The SPD did not differ significantly in brain concussion, or diffuse, focal and combined brain injury groups compared with the control group. The CMCT was prolonged in patients with diffuse and combined brain lesions. Among subjective complaints only fatigue was significantly related to ITD, MEP, and SP threshold abnormalities.
CONCLUSIONS—The results suggest that mechanisms involved in MEP and SP generation are differently affected in head injury, the first being impaired more severely. The increase of the ITD accompanied by reduction of the MEP/M wave amplitude ratio may reflect a dissociated impairment of inhibitory and excitatory components of central motor control in head trauma.


Short Duration Transient Visual Evoked Potentials in Glaucomatous Eyes

Purpose: To investigate the correlation between structural and functional damage in patients with asymmetric glaucoma using a newly developed short duration transient visual evoked potential (SD-tVEP) device.Methods: Twenty-five patients with visual acuity >= 20/30 and asymmetric visual field (VF) loss [inter-eye difference in mean deviation index (MD) of at least 3 dB] were enrolled. Patients underwent optical coherence tomography (OCT) for macular thickness measurement, scanning laser polarimetry with variable corneal compensation for retinal nerve fiber layer measurement, and SD-tVEP (10% and 85% Michelson contrast, acquisition time of 20 s) in both eyes within 2 months. We correlated VF MD and structural test results with SD-tVEP P100 latency and Delta Amplitude (N75-P100).Results: Using 10% contrast, there was a significant difference in SD-tVEP latency and amplitude between eyes with better and worse VF MD (P 0.33, P <= 0.01). When using 85% contrast, SD-tVEP amplitude differed between eyes (P = 0.01) and MD values correlated significantly with amplitude results (r = 0.32, P = 0.01), but not with latency (P = 0.46). in eyes with more advanced VF loss, there was a positive and significant correlation between SD-tVEP amplitude (85% contrast) and macular thickness on OCT (r = 0.47, P = 0.01), but not with retinal nerve fiber layer measured with polarimetry (P = 0.26).Conclusions: in cases of asymmetric glaucoma, SD-tVEP results correlate significantly with the level of VF damage as measured by MD. in the eyes with more advanced VF loss, reduced SD-tVEP amplitude was associated with decreased macular thickness on OCT. These findings suggest that SD-tVEP may be a fast and objective method to assess or screen for functional damage in glaucomatous eyes.Diopsys, IncNew York Eye & Ear Infirm, Dept Ophthalmol, Einhorn Clin Res Ctr, New York, NY 10003 USANYU, Dept Ophthalmol, Sch Med, New York, NY 10016 USANew York Med Coll, Dept Ophthalmol, Valhalla, NY 10595 USAUniversidade Federal de São Paulo, Dept Ophthalmol, São Paulo, BrazilDiopsys Inc, Pine Brook, NJ USAUniversidade Federal de São Paulo, Dept Ophthalmol, São Paulo, BrazilWeb of Scienc