A clinical study of corticospinal and peripheral conductions to proximal lower limb muscles

Upper motor neuron assessment in amyotrophic lateral sclerosis using the patellar tendon reflex and motor-evoked potentials to the lower limbs

Amyotrophic lateral sclerosis (ALS) diagnosis relies on signs of progressive damage to both lower motoneuron (LMN), given by clinical examination and electromyography (EMG), and upper motoneuron (UMN), given by clinical examination only. Recognition of UMN involvement, however, is still difficult, so that diagnostic delay often remains too long. Shortening the time to clinical and genetic diagnosis is essential in order to provide accurate information to patients and families, avoid time-consuming investigations and for appropriate care management. This study investigates whether combined patellar tendon reflex recording with motor-evoked potentials to the lower limbs (T-MEP-LL) is relevant to assess corticospinal function in ALS, so that it might serve as a tool improving diagnosis. T-MEP-LL were recorded in 135 patients with suspected motor neuron disease (MND) from February 2010 to March 2021. The sensitivity, specificity, and ability to improve diagnosis when added to Awaji and Gold Coast criteria were determined. The main finding of the study is that T-MEP-LL can detect UMN dysfunction with a 70% sensitivity and 63% specificity when UMN clinical signs are lacking. The sensitivity reaches 82% when considering all MND patients. Moreover, at first evaluation, using T-MEP-LL to quantify reflex briskness and to measure central conduction time, can improve the diagnostic accuracy. T-MEP-LL is easy to perform and does not need any electrical stimulation, making the test rapid, and painless. By the simultaneous quantification of both UMN and LMN system, it could also help to identify different phenotype with more accuracy than clinical examination in this broad-spectrum pathology. The question whether T-MEP-LL could further be a real biomarker need further prospective studies.

Combined tendon reflex and motor evoked potential recordings in amyotrophic lateral sclerosis

OBJECTIVE

This retrospective (case-control) collaborative study evaluates tendon reflex recordings combined with transcranial magnetic stimulation motor evoked potentials recordings (T-MEPs) at lower limbs in amyotrophic lateral sclerosis (ALS).

METHODS

T-MEPs were recorded in 97 ALS patients distinguished according to their patellar reflex briskness. Patients' electrophysiological data were compared with values measured in 60 control patients matched for age and height. Correlations studies between parameters or with some patients' clinical characteristics were also performed.

RESULTS

The central motor conduction time yields the highest sensitivity (82%) and specificity (93%), allowing twice more upper motor neuron (UMN) dysfunction detection than clinical examination, and being more altered in late stages of the disease. The T response to MEP response amplitude ratio (T/MEP ar) is nearly as sensitive to detect ALS and better identifies abnormal hyperreflexia. It is not correlated with evolutive stage, contrarily to conduction time-related parameters. In addition, T-MEPs detect asymmetries escaping clinical examination.

CONCLUSIONS

The corticospinal conduction to lower limbs is slowed in ALS. The T/MEP ar helps deciding when patellar reflexes are abnormal in a given patient suspected of ALS.

SIGNIFICANCE

The T-MEP technique provide powerful electrophysiological biomarkers of UMN involvement in ALS. This simple and painless procedure introduces the clinically useful concept of electrophysiological hyperreflexia and might be expanded to future exploration of proximal upper limbs and bulbar territories.

Impaired conduction of Ia sensory fibers in multifocal motor neuropathy: An electrophysiological demonstration

Objectives

To report the clinical and electrophysiological findings in two patients with multifocal motor neuropathy (MMN) and bilateral absent patellar and Achilles tendon reflexes despite normal strength of quadriceps and calf muscles.

Methods

The medical history and clinical evaluation were completed by electrophysiological tests: sensory and motor nerve conduction studies, needle electromyography, motor-evoked potentials (MEPs) after transcranial magnetic stimulation, patellar T (tendon) responses, quadriceps and soleus H (Hoffman) reflex recordings.

Results

In the two patients, history, clinical evaluation, nerve conduction studies, favorable response to intravenous immunoglobulins, and positive anti-GM1 antibodies fulfilled the diagnosis of MMN. The lower limbs were asymptomatic, except for a unilateral weakness of foot dorsiflexion. The patellar and Achilles tendon reflexes disappeared during the course of the disease. The sensory nerve conduction studies were normal or minimally modified, M-wave and MEP/M amplitude ratio to the quadriceps were normal, patellar T (tendon) responses were virtually absent, and H-reflex to the quadriceps and soleus muscles were absent.

Conclusions

These observations, which show the interruption of the reflex afferent pathway, raise the question of Ia afferent involvement in the lower limbs of these two patients with MMN. Further investigations should determine the frequency and significance of these findings in this disorder.

Four-pulse transcranial magnetic stimulation using multiple conditioning inputs. Normative MEP responses

A four-pulse pattern of transcranial magnetic stimulation (TMS) was compared to traditional dual-pulse TMS for its ability to modulate motor cortical excitability. This novel pattern consisted of a three-pulse train of subthreshold conditioning pulses followed by a suprathreshold test pulse (i.e., SC-T). The intervals between these superconditioning (SC) pulses (1, 3, or 6 ms) and the follow-on test pulse (1, 3, 10, or 25 ms) were varied, and the resultant MEPs were compared to those elicited by: (1) single-pulse TMS; and (2) dual-pulse conditioning-test (C-T) TMS with either short (3 ms) or long (10 ms) intervals to elicit short-interval intracortical inhibition (SICI) or intracortical facilitation (ICF), respectively. Testing included abductor pollicis brevis (APB) and tibialis anterior (TA) in 15 neurologically normal adults. For superconditioning inputs, 10 ms test intervals caused especially strong facilitation of the test MEP, while 1 ms test intervals were particularly effective at causing inhibition of the test response. For both muscles and across all subjects, the most effective of the 12 SC-T inputs tested for causing either facilitation or inhibition was-with rare exception-superior to the dual-pulse TMS input for causing facilitation (i.e., ICF) or inhibition (i.e., SICI), while the overall magnitude of effect was more pronounced in APB compared to TA. Nevertheless, after normalization, the impact of a superconditioning input train on the test MEP was similar in APB and TA muscles, suggesting similar mechanisms of action. Limited findings from a single subject with amyotrophic lateral sclerosis (ALS) are included to further illustrate the potential advantages of using a train of conditioning pulses preceding a TMS test pulse to selectively investigate abnormal motor cortical excitatory and inhibitory circuitry.

The accuracy of subjective clinical assessments of the patellar reflex

INTRODUCTION

Measurement precision and accuracy of spinal reflexes plays an essential role in the clinical neurological examination. Reflexes are conventionally assessed either electromyographically or with rating scales. In this study we compared objective kinematic T-reflex and subjective assessments of patellar reflexes in 15 normal healthy subjects.

METHODS

Randomized recordings of objectively quantified reflexes were rated by 24 medical students, 16 general practitioners, and 12 neurologists, using a visual analog scale and the NINDS and Mayo clinical reflex scales.

RESULTS

For all groups of raters, Spearman rank correlations showed that subjective ratings significantly correlated with change of knee angle (R2 = 0.72-0.79, P < 0.001) and maximum T-reflex amplitude (R2 = 0.84-0.94, P < 0.001). Stepwise multiple regression analysis showed that all subjective rater groups relied most on the change of knee angle to assess the reflex.

CONCLUSIONS

These findings show that subjective assessments of reflexes using reflex rating scales correlate strongly with biomechanical and electromyographic measures.