Optimising the detection of upper motor neuron function dysfunction in amyotrophic lateral sclerosis?a transcranial magnetic stimulation study

Abstract

Evidence of upper motor neuron (UMN) dysfunction is essential in making the diagnosis of amyotrophic lateral sclerosis (ALS). Central motor conduction (CMC) abnormalities detected using transcranial magnetic stimulation (TMS) are presumed to reflect UMN dysfunction. CMC is, however, often normal in patients with classical sporadic ALS. The aim of the study was to determine whether the utility of the CMC measure in ALS could be enhanced. We measured CMC to four pairs of muscles (abductor digiti minimi (ADM), biceps, vastus medialis (VM) and abductor hallucis (AH) in 20 controls and 25 ALS patients. The commonest abnormality detected in the ALS patients was an absent MEP, found in 11 patients (44 %) and in 25 of 200 muscles examined. Studying a minimum of three muscles increased the probability of detecting UMN dysfunction. Weakness in the muscle as well as selecting a distal rather than a proximal muscle was significantly associated with an abnormal CMC. Interside differences in CMC were significantly more pronounced in the patient group. In 30% of patients a significant interside difference in AH CMC time was the sole abnormality, suggesting mild UMN dysfunction on the side with the longer CMC.

Congenitally altered motor experience alters somatotopic organization of human primary motor cortex

“…The similarity of the MEP latencies from lateral and medial M1 area, the similarity of latencies with normative values in the published literature (25,26,32), and the small variability of these latencies favor a mono-synaptic corticospinal projection from both the medial and lateral M1 (22,23). TMS has been reported to activate oligosynaptic pathways as well, such as corticoreticulospinal and corticopropriospinal projections (33).…”

“…3). The latencies of the MEPs in the targeted foot muscle (AH) that were evoked by TMS over both the medial and the lateral hot spots were within the 95% confidence interval of reported latencies for this muscle (25)(26)(27). Within each subject, these laten- In Fü sslers S1-S3, activation in the precentral gyrus is significantly (P Ͻ 0.001 uncorrected) stronger for toe movements of the dominant (C) and nondominant (D) foot when contrasted with 9 control subjects (activation superimposed on the individual T1-weighted MR image of subject S1, z ϭ 66).…”

Magnetic stimulation including the triple‐stimulation technique in amyotrophic lateral sclerosis

“…One of our most striking findings is that TMS was more sensitive than clinical examination in patients with suspected or possible ALS, revealing UMN dysfunction in 75% (9 of 12) of the upper limbs. The sensitivity of CMCT in supporting the diagnosis reportedly increases with the number of muscles studied, 10,12,14,35,38,40,47 and this may apply to the parameters studied herein. We believe that, as for electromyography, several regions of the body, including muscles innervated by bulbar nerves, should be tested to increase the sensitivity of TMS in supporting a diagnosis of ALS.…”

“…Transcranial magnetic stimulation (TMS) is a useful tool for diagnosing UMN dysfunction in ALS and provides a sensitive means of assessing cortical excitatory and inhibitory dysfunction. 10,12,14,35,38,40,47 The most frequently studied variables, which are generally recorded by conventional TMS using simple stimulation techniques, are central motor conduction time (CMCT), amplitude of motor evoked potentials (MEPs), resting motor threshold (RMT), and duration of silent period (SP). CMCT is reportedly not a sensitive variable for the diagnosis of ALS.…”

Amyotrophic Lateral Sclerosis and Primary Lateral Sclerosis

“…These techniques may provide evidence of UMN pathology in PLS and ALS, but may be more sensitive to the primary pathology in PLS than ALS [156][157][158][159]. These techniques may provide evidence of UMN pathology in PLS and ALS, but may be more sensitive to the primary pathology in PLS than ALS [156][157][158][159].…”