Diagnostic role of triple stimulation technique in patients with multifocal motor neuropathy

Abstract

To detect the conduction block (CB) between nerve root and Erb's point by triple stimulation technique (TST) in patients with multifocal motor neuropathy (MMN). The subjects were recruited from Peking University Third Hospital during the period of April 2010 to April 2011. Twelve MMN patients, 30 healthy subjects, 30 patients with cubital tunnel syndrome and 30 patients with amyotrophic lateral sclerosis (ALS) underwent TST along with clinical assessments and nerve conduction studies. TST combined transcranial magnetic stimulation (TMS) of motor cortex with peripheral collision studies. The results were expressed by the TST amplitude ratio. And the conduction block was judged by TST amplitude ratio or the amplitude ratio of compound muscle action potential (CMAP). The TST amplitude ratio of healthy volunteers was 93.0% ± 2.7%. And it was 42.3% ± 7.1% in patients with MMN indicating a proximal CB. There were 47 CBs in distal segments by routine nerve conduction study. Compared with the baseline levels, the patients with definite MMN increased (χ(2) = 6.31, P < 0.05). The TST amplitude ratio (30.5% ± 4.8%) of those with ALS indicated the lesion of pyramid tract (t = 2.43, P < 0.05). And the TST amplitude ratio (92.2% ± 2.6%) of those with cubital tunnel syndrome was normal (t = 0.68, P > 0.05) while the nerve conduction velocity of cubital tunnel syndrome patients (below elbow-above elbow) was slower ((23.6 ± 3.5) m/s) (t = 2.00, P < 0.05). TST may be used to detect proximal CB and facilitate the diagnosis of MMN.