Effects of 1-Hz repetitive transcranial magnetic stimulation on long-latency reflexes and cortical relay time.

Long-latency reflexes (LLRs) of hand muscles include a transcortical component. Cortical relay time estimated by the subtraction of motor and somatosensory evoked potentials from LLR reflects the physiology of the central neural pathway of LLR. It is believed that 1-Hz repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex can decrease cortical excitability for approximately 15 minutes at intracortical level. The aim of the study was to analyze LLR and cortical relay time before and after 1-Hz rTMS. Long-latency reflex and H reflex obtained from the thenar muscles by electrical stimulation of the median nerve of 16 healthy subjects. Additionally, motor evoked potentials and somatosensory evoked potentials were also recorded. Cortical relay time was calculated by the subtraction of motor evoked potential and somatosensory evoked potential latencies from LLR. These electrophysiologic recordings were performed before and after 15 minutes of 1-Hz rTMS over the motor area for the thenar muscles in the primary motor cortex. The amplitudes of LLR and motor evoked potential were significantly decreased after rTMS, but the H reflex of the thenar muscle and somatosensory evoked potentials were unchanged. The major finding of our study was a shortened duration of cortical relay time after rTMS. In conclusion, our findings suggest that the LLR of the thenar muscles has a transcortical pathway and cortical relay time that can give some information about the physiology of the intracortical pathway of LLR.

Adductor T reflex abnormalities in patients with decreased patellar reflexes.

The adductor reflex (AR) is a tendon reflex that has various features that differ from other tendon reflexes. This reflex was tested in different disorders presenting with diminished patellar reflexes such as diabetic lumbosacral radiculoplexus neuropathy (DLRPN), L2-L4 radiculopathy, and distal symmetric diabetic neuropathy (diabetic PNP). The AR and crossed-AR (elicited by tapping the contralateral patellar tendon) were recorded using concentric needle electrodes. Additionally, the patellar T reflex (vm-TR) and vastus medialis H reflex (vm-HR) were recorded using surface electrodes. AR was recorded in only one out of eight patients with DLRPN, but it was recorded in 21 out of 22 patients with L2-L4 radiculopathy (95.5%). Of these reflexes, only AR showed prolonged latency in the L2-L4 radiculopathy group. The latencies of AR, vm-TR, and vm-HR were prolonged in patients with diabetic PNP. We conclude that AR can be useful in the differential diagnosis of some lower motor neuron disorders that present with patellar reflex disturbance. Muscle Nerve 40: 264-270, 2009.