Department of Neurosciences, S. Maria della Misericordia Hospital, Udine, Italy Anna Scalise CORTICAL EXCITABILITY IN RLS: TMS STUDIES

Diagnosis of RLS is currently based on the presence of specific clinical symptoms. ……. … but the patho-physiology?!

……. Is the RLS a disease involving only the PNS? …… Is the RLS a disease involving only the CNS? ……. Is the RLS a disease involving both the PNS and the CNS?

RLS and the alterations at the Spinal level Recent studies investigated whether RLS patients have spontaneous changes in H-reflexes or show altered reflex patterns after (external) inhibition or excitation of the relevant spinal segment. The authors found a diminished inhibition at spinal level in PLMD patients. This is probably due to altered function of the descending spinal tracts, peripheral influence or changes at the inter-neural circuitry at spinal level itself, or combinations of these 3 possibilities. These results stress the importance of the diminished descending inhibitory pathways resulting in a down regulation of inhibition at the spinal level. Clin Neurophysiol 2005;116: Rijsman et al Clin Neurophysiol 2005;116:

Is there an alteration of cortical excitability in RLS? Is the motor excitability influenced by the treatment with a dopamine agonist in RLS ? Is therapy with dopamine agonists able to modify the neuro-physiological findings in RLS?

TMS & RLS STUDIES Motor system excitability in patients with restless legs syndrome. Tergau et al Neurology 1999;52:1060 Change in excitability of motor cortical circuitry in primary restless legs syndrome. Entezari-Taher et al Neurology 1999;53:1201 Motor pattern of periodic limb movement during sleep. Provini F et al Neurology 2001;57:300 Neurophysiological study of corticomotor patways in restless legs syndrome. Quatrale et al. Clin Neurophysiol 2003;114(9):1638 Cortical silent period is shortened in restless legs syndrome independently from circadian rhythm. Stiasny-Kolster et al. Suppl Clin Neurophysiol 2003;56: These authors, despite some differences, conclude that the pyramidal tract is intact in RLS patients, but that the inhibitory system is altered, suggesting a cortical– subcortical origin of the disease.

TMS & RLS…our point of view ! Absence of postexercise and delayed facilitation of motor cortex excitability in restless legs syndrome: evidence of altered cortical plasticity? Scalise A, Pittaro-Cadore I, Golob EJ, Gigli GL, Sleep 2006;29(6): Sleep 2006;29(6): Motor cortex excitability in restless legs syndrome. Scalise A, Pittaro-Cadore I, Gigli GL, Sleep Medicine 2004;5(4):393-6 Sleep Medicine 2004;5(4):393-6

Eleven patients, affected by primary RLS and eleven healthy subjects, age and gender matched, underwent transcranial magnetic stimulation studies, using both the single pulse TMS and the paired-pulse TMS. Absence of postexercise and delayed facilitation of motor cortex excitability in restless legs syndrome: evidence of altered cortical plasticity? Scalise A, Pittaro-Cadore I, Golob EJ, Gigli GL, Sleep 2006;29(6):

For each subject three experimental sessions were performed: 1) 1) Evaluation of MEPs parameters: motor threshold, MEP amplitude, and silent period duration were measured in response to single-pulse magnetic stimulation. 2) 2) Paired-pulse stimulation: the time course of intracortical motor activity was tested using pairs of magnetic stimuli (1- to 6-ms interstimulus intervals). 3) 3) Motor task: cortical excitability was investigated by using single magnetic stimuli before and after a motor task. Experimental procedures

Muscles contraction, immediately after the MEP, is followed by an electrical silence period that interrupts the ongoing EMG activity, a phenomenon which is named “silent period”. The duration of the silent period was shorter in RLS subjects compared to controls, a result which is consistent with some previous studies. The silent period is considered an indicator of inhibitory activity within primary motor cortex. Single-pulse stimulation

Silent Period Duration Mean 41.8 ms Mean 58.7 ms *

The RLS group showed a marked decrease in central motor inhibition assessed by using paired- pulse TMS at short inter-stimulus intervals (a conditioning TMS pulse presented shortly before a test pulse reduces MEP amplitudes to the test pulse in controls, but not in RLS). Reduced paired-pulse inhibition in RLS is consistent with previous studies Paired-pulse stimulation

Control-subject RLS-patient

FIGURE 1

Single-pulse TMS MEPs were recorded from the first dorsal interosseous muscle (FDI) of the left nondominant hand. A round coil (90 mm) was used, and the lateral edge was placed over the presumed hand area. A moderate contraction allowed the detection of MEP parameter in the 500 ms following TMS. Stimulus intensity during the test execution was determined by adding an intensity equal to 5% of the maximum stimulus output above the motor threshold.

MotorTaskMotorTaskMotorTaskMotorTask In order to perform the motor task, subjects carry out bilateral, repetitive opening and closing movements of the index finger toward the thumb with both digits extended (3-4 movements per second). Three different exercise periods (lasting 30, 60, and 90 seconds respectively) were given to the subjects in progressive order (i.e., first session: 30 seconds; second session: 60 seconds; third session: 90 seconds).

baseline60 s of esercise 30 s of esercise 90 s of esercise 15 m of rest baseline 30 s of ex. 60 s of ex. after rest 90 s of ex. Post-exercise facilitation Delayed facilitation

* Post-exercise facilitation Delayed facilitation

Considerations The physiology of delayed facilitation is not completely clarified, but it seems to involve enduring changes in synaptic strength. During a motor task, the repeated activation of excitatory synapses in the central nervous system may possibly change the neural circuit dynamics and modify the cortical excitability. The induced short-term potentiation, long-term potentiation, and/or unmasking of existing synapses onto motor cortex neurons, represent the neural substrates of physiological learning processes, an important mechanism of practice dependent plasticity. Caramia MD, Scalise A, Gordon R, Michalewski HJ, Starr A Clin Neurophysiol 2000;111: Starr A, Scalise A, Gordon R, Michalewski HJ, Caramia MD Clin Neurophysiol 2000;111:

Considerations In RLS patients the motor task did not affect the cortical excitability; in fact the “Delayed facilitation” was absent. In RLS we hypothesize an alteration in the processes of the “motor skill learning” … ….. a reduction or an alteration in movement-related cortical plasticity …… and which is the role of Dopamine?!

Spinal level and Dopamine In previous studies is suggested that the origin of PLMS can be a result of disinhibition of segmental spinal pathways by interruption of descending spinal pathways. Lee et al., 1996 and Hogl et al., Changes in spinal cord excitability is also supposed by the finding of lower thresholds and greater spatial spread of the spinal flexor reflexes in RLS with PLMS. Bara-Jimenez et al., 2000 The positive reaction to dopaminergic medications and the presence of dopaminergic terminals (group A11) in the spinal dorsal horn as well as in the vicinity of the motor neuron in the ventral horn, provide support to the hypothesis of a functional role of dopamine in the spinal motor control mechanism. Lindvall et al., 1983 and Ondo et al., 2000 Bara-Jimenez et al., 2000

Cortical plasticity and Dopamine Dopamine plays an important role in synaptic plasticity, involving motor cortex and regions of the basal ganglia. Dopamine plays an important role in synaptic plasticity, involving motor cortex and regions of the basal ganglia. Centonze Et al Eur J Neurosci 2001;13: The brain synaptic plasticity in the corticostriatal circuit depends on the activation of dopamine receptors such as those in the prefrontal cortex, in the hippocampus and in the amygdala. The brain synaptic plasticity in the corticostriatal circuit depends on the activation of dopamine receptors such as those in the prefrontal cortex, in the hippocampus and in the amygdala. Calabresi et al Lancet Neurol Nov;5(11): Review. Dopamine might modulate cortical plasticity, which could be related to higher order motor control, including motor learning. In particular, processes such as practice-dependent plasticity are enhanced by dopamine. Dopamine might modulate cortical plasticity, which could be related to higher order motor control, including motor learning. In particular, processes such as practice-dependent plasticity are enhanced by dopamine. Meintzschel Cereb Cortex Aug;16(8): Epub 2005 Oct 12. We suggest that in RLS the alterations in movement-related cortical plasticity could be resulting from a dopaminergic dysfunction

TMS & RLS & THERAPY STUDIES Kutukcu Y, Dogruer E, Yetkin S, et al. Evaluation of periodic leg movements and associated transcranial magnetic stimulation parameters in restless legs syndrome. Muscle Nerve Jan;33(1): Nardone R, Ausserer H, Bratti A, et al. Cabergoline reverses cortical hyperexcitability in patients with restless legs syndrome. Acta Neurol Scand Oct;114(4): Gorsler A, Liepert J. Influence of carbegoline on motor excitaility in patients with restless legs syndrome. J Clin Neurophysiol 2007;24: These authors, despite some differences, conclude that some TMS parameters could be influenced by treatment with dopamine agonists

TMS & RLS & THERAPY…our point of view! Changes of cortical plasticity after dopaminergic-treatment in restelss legs syndrome Scalise A, Pittaro-Cadore I, Janes F, Marinig R, Gigli GL. submitted

TMS: PRE e POST Therapy TMS: PRE e POST Therapy Twelve right-handed patients (8 woman and 4 men, mean age 52.7 ±11.4 years), affected by primary (idiopathic) RLS, were included in our study and underwent to TMS studies both in basal condition and after a month of dopaminergic treatment with pramipexole. (dose di 0.18 mg\die) After a month of treatment, all patients reported a significant improvement of RLS symptoms

Following pharmacological treatment, RLS patients show a marked increase of the central motor inhibition, assessed by using paired-pulse TMS at short inter- stimulus intervals. On the contrary, the duration of the silent period from the muscles of the upper limbs was unchanged in RLS patients after treatment, compared to the pre- treatment condition. These results confirm the findings of the others studies Central motor inhibition

Paired-pulse stimulation

Motor task SMT “traces” RLS-patient pre-therapy Control subject RLS-patient post-therapy baseline 30 s of ex. 60 s of ex. after rest 90 s of ex. baseline 30 s of ex. 60 s of ex. after rest 90 s of ex. baseline 30 s of ex. 60 s of ex. after rest 90 s of ex.

PRE and POST Treatment PRE and POST Treatment * Delayed facilitation Post-exercise facilitation

Considerations In RLS patients the motor task affects the cortical excitability after the dopaminergic treatment,; mainly the “Delayed facilitation ”reappears. In RLS we suppose that the dopaminergic treatment “restore” the alterations in the processes of the “motor skill learning” … …we can conclude that the alterations in movement-related cortical plasticity in RLS …..could be the result of a dopaminergic disfunction. In RLS patients the motor task did not affect the cortical excitability; in fact the “Delayed facilitation” is absent. In RLS we hypothesize an alteration in the processes of the “motor skill learning”... a reduction or an alteration in movement-related cortical plasticity …. and which is the Dopamine role?! Conclusions

CNS Dopaminergic dysfunction Alterations in movement related cortical plasticity RLS PNS

….. Central Nervous System structures seems involved in RLS pathophysiology…… ….. functional alterations at Peripheral Nervous System level could reverberate across the spinal cord to the cortical-subcortical regions, that triggering the neurotransmitter modifications cause the RLS clinical manifestations. RLS could be considered a multi-factorial result of many neuronal circuits involvement, the dopaminergic system seems to play the most crucial role

So far no etiopathogenetic hypothesis seems to be exhaustive…. Every hypothesis seems to be an essential element of the puzzle but ….. lack the last plug to complete the picture! Since TMS is able to disclose SNC alterations and can follow the time and drug related modifications, it may became, in the future, a diagnostic tool for the evaluation of the RLS.