Transcranial magnetic stimulation in lower motor neuron diseases.
OBJECTIVE
To study the diagnostic value of transcranial magnetic stimulation (TMS) in a group of patients with lower motor neuron disease (LMND). Among LMND, several chronic immune mediate motor neuropathies may simulate amyotrophic lateral sclerosis (ALS).


METHODS
Forty patients with LMND were included TMS was performed at the first visit. The patients were seen prospectively every 3 months for a period of 1-4 years.


RESULTS
Three different groups were distinguished at the end of follow-up: (1) ALS group with 7 patients, (2) Pure motor neuropathy with 14 patients and (3) Other LMND including 12 patients with hereditary spinal amyotrophy, 3 patients with Kennedy's disease and 4 patients with post-poliomyelitis. On the basis of the results of TMS variables, 6 out of 7 ALS patients had abnormality of silent period (SP) associated or not with abnormality of excitatory threshold or amplitude ratio. Patients with pure motor neuropathy had normal SP and amplitude ratio. Four out of 14 patients had increased central motor conduction time (CMCT), one had increased CMCT and excitatory threshold, and one patient had a slightly increased excitatory threshold. Considering the abnormality of TMS variables in the groups, SP, excitatory threshold, and amplitude ratio were chosen in a post-hoc attempt to select variables yielding high sensitivity and specificity. The overall sensitivity of TMS for diagnosis of ALS among LMND was 85.7%, its specificity was 93.9%. When only the abnormality of SP was taken into account, the sensitivity was unchanged. But the specificity was improved to 100%.


CONCLUSIONS
TMS helped to distinguish suspected ALS from pure motor neuropathy.
Attarian
S
S
Department of Neurology and Neuromuscular Diseases, CHU La Timone, 264 rue Saint-Pierre, 13385 Marseilles, France. sattarian@ap-hm.fr
Azulay
J-Ph
JP
Lardillier
D
D
Verschueren
A
A
Pouget
J
J
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000187:drug effects; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000503:physiopathology / Q000628:therapy*; D009431:Neural Conduction / Q000528:radiation effects; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011930:Reaction Time / Q000528:radiation effects; D012680:Sensitivity and Specificity; D012684:Sensory Thresholds / Q000528:radiation effects; D018709:Statistics, Nonparametric; D050781:Transcranial Magnetic Stimulation