Transcranial magnetic stimulation of motor pathways directed to muscles supplied by cranial nerves in amyotrophic lateral sclerosis.
OBJECTIVE
In amyotrophic lateral sclerosis (ALS), transcranial magnetic stimulation (TMS) detects remarkable abnormalities of central motor circuits: cortical excitability threshold, silent period (SP) duration and intra-cortical inhibition. TMS directed to cranio-facial musculature was performed in ALS patients in order: (1) to document the neurophysiological involvement of motor central and peripheral cranial pathways by evaluating changes of threshold and SP; (2) to discover a possible correlation between the clinical picture and abnormal excitability properties.


METHODS
Motor evoked potentials (MEPs) were recorded from masseter, genioglossus and orbicularis oris muscles of both sides in 25 ALS patients and 25 controls, in response to TMS delivered over the face M1 area and the vertex.


RESULTS
TMS gave rise to two orders of responses: bilateral MEPs during contraction represented the central responses, and motor action potentials (MAPs) during rest represented the peripheral responses. MEPs were followed by SPs, which increased linearly with increasing TMS intensity (r=0.8). At least one of the analyzed parameters was abnormal in all patients: central abnormalities (increased active threshold, delayed MEPs, reduced SP) were found in 96% of patients, alone or combined with abnormalities of the MAPs (reduced area and/or prolonged latency). The reduction of SP was linearly related to the Norris score (r=0.95).


CONCLUSIONS
Our study shows that TMS is able to detect the involvement of multiple cranial muscles in ALS. This finding offers often pre-clinical information about the disease picture. Therefore, it can be employed as a valuable means for early diagnosis.
Desiato
Maria Teresa
MT
Clinica Neurologica, Dipartimento di Neuroscienze, Università Tor Vergata, Ospedale S. Eugenio, Piazzale Umanesimo, 10, 00144 Rome, Italy.
Bernardi
Giorgio
G
Hagi H
Abdikarim
A
Boffa
Laura
L
Caramia
Maria D
MD
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D003391:Cranial Nerves / Q000503:physiopathology*; D004574:Electromagnetic Fields; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology*