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Abstract The aims of this study were to identify the motor cortical representation of the diaphragm and to assess the corticodiaphragmatic pathway from both hemispheres. Specially designed bipolar surface electrodes were used to record the ipsilateral and contralateral compound motor evoked potentials (CMEPs) of the diaphragm after transcranial magnetic stimulation (TMS) of the motor cortex. In addition, the response to cervical magnetic stimulation of the phrenic nerve roots, effected using a figure-of-eight magnetic coil, was also recorded. The study involved 30 normal adult male volunteers. The average point of optimal excitability (POE) was determined to be 3.7 cm lateral to the mid-sagittal plane and 0.89 cm anterior to the preauricular plane. The largest response was obtained at a stimulus coil orientation of 0-90 degrees. The TMS of either hemisphere produced CMEPs in the contralateral and ipsilateral diaphragm muscles. TMS of either hemisphere elicited CMEPs that had significantly greater amplitudes and shorter latencies from the contralateral muscles compared with the ipsilateral response (P0.0001). The central motor conduction time of the crossed tract (8.8 ms) was significantly shorter than that of the uncrossed tract (12.2 ms). No significant interhemispheric differences were recorded. The recorded CMEPs recorded in response to TMS were facilitated during volitional inspiration. Phrenic nerve latency was 5.7 ms and 5.6 ms for the right and left phrenic nerves, respectively, with no significant difference between these values. Both bilateral crossed and uncrossed corticospinal connections to the diaphragm were usually present, with the crossed tract predominating. The technique used in this study may be useful for investigations into the function and integrity of central and peripheral pathway of the diaphragm muscles in various neurological disorders.

Abstract The purpose of this study is to evaluate objectively the functional changes in the nervous system in hypothyroidism by different electrophysiological parameters and to determine the frequencies of these changes in patients with hypothyroidism. We enrolled 23 patients (17-64 years old, mean 38.2) with biochemical evidence of hypothyroidism, with thyroxine less than 4 microg/dl and thyrotropin above 4.5 mU/ml, and 200 age- and sex-matched normal subjects. Detailed clinical examination and electrophysiological measurements included electromyography, motor conduction velocity, visual-evoked potentials (VEPs), brainstem auditory-evoked potentials (BAEPs) and event-related potentials. Determinations of P300, Wechsler Adult Intelligence Scale (IQ) and electroencephalography (EEG) were performed. Of the hypothyroid patients 52% had peripheral nervous system (PNS) involvement. Entrapment neuropathy was the commonest (35%). Axonal neuropathy was recorded in 9% and myopathy was recorded in another 9%. The central nervous system (CNS) was affected in 78% of the cases. Significant prolongations of P100 latency of VEP, latency and interpeak latency of BAEPs of different waves of hypothyroid patients were compared to the control group. 52% had abnormal VEPs and BAEPs above the mean +/- 2 SD of the normal control group. Six patients (26%) had prolonged P300 latency while 16 patients had an IQ below 90. Eight patients (35%) had EEG changes. Diffuse slowing of background activity was the commonest. No significant correlation was observed between hormonal levels and the different electrophysiological parameters. Thus, the CNS is more vulnerable to the effect of hypothyroidism than the PNS. Therefore, we suggest performing electrophysiological studies in hypothyroid patients, even in the asymptomatic ones, early in the course of disease in order to detect the nervous system involvement.