François-Charles Wang

Normalizing shoulder EMG: An optimal set of maximum isometric voluntary contraction tests considering reproducibility

Normalization of the electromyography (EMG) signal is often performed relatively to maximal voluntary activations (MVA) obtained during maximum isometric voluntary contraction (MVIC). The first aim was to provide an inter-session reproducible protocol to normalize the signal of eight shoulder muscles. The protocol should also lead to a level of activation >90% of MVA for >90% of the volunteers. The second aim was to evaluate the influence of the method used to extract the MVA from the EMG envelope on the normalized EMG signal. Thirteen volunteers performed 12 MVICs twice (one week interval). Several time constants (100ms to 2s) were compared when extracting the MVA from the EMG envelope. The EMG activity was also acquired during an arm elevation. Our results show that a combination of nine MVIC tests was required to meet our requirements including reproducibility. Both the number of MVIC tests and the size of the time constant influence the normalized EMG signal during the dynamic activity (variations up to 15%). A time constant of 1s was a good compromise to extract the MVA. These findings are valuable to improve the reproducibility of EMG signal normalization.

iMAX: a new tool to assess peripheral motor axonal hypoexcitability

https://doi.org/10.1016/j.clinph.2017.09.111 1388-2457/ 2017 International Federation of Clinical Neurophysiology. In routine electrodiagnostic procedures, classical parameters allow assessment of motor unit loss/reinnervation (CMAP amplitude) and motor conduction slowing (motor distal latency, motor conduction velocity, F waves), but none evaluates peripheral motor axon hypoexcitability. Yet everyone has experienced that in a demyelinating neuropathy it is often necessary to increase above normal the amount of current to obtain a supramaximal motor response. Excitability properties of human peripheral nerves can be assessed by various neurophysiological methods (Brismar, 1985; Kiernan et al., 2000; Burke et al., 2001), but they are not often used in daily practice because they are time consuming and they require a specific collection system and software. The median nerve innervated thenar muscles were studied here with classical motor nerve conduction settings. The ground and recording electrodes consisted of pre-gelled disposable surface electrodes (Alpine Biomed, REF 9013L0453). The recording electrode was placed over the thenar eminence in close proximity to the muscle endplates halfway between the midpoint of the distal wrist crease and the first metacarpophalangeal joint. The reference electrode was placed over the proximal phalanx of the thumb. The ground electrode was placed over the ventral part of the forearm. All data were collected by the same investigator using a Keypoint G3 EMG machine (Natus Medical Incorporated). Compound motor responses were evoked by 1ms constant current square waves through bipolar surface stimulation with two 7 mm diameter felt tip pads, 2.3 cm apart (Natus Medical Incorporated, REF 9013L0362). Despite the fact that previous studies showed that motor nerves have lowest threshold with a stimulus duration of typically 0.2 ms, while sensory nerves can be excited at lowest threshold with a stimulus duration of 1.0 ms (Panizza et al., 1992), we used the longest stimulus duration of 1 ms in order to have if necessary the greater amount of current and to avoid technical limitation in the case of a severe motor axon hypoexcitability. The cathode was 2 cm proximal from the distal wrist crease and the anode was 2.3 cm proximal from the cathode. The bandpass filter setting was set from 2 to 5000 Hz. In accordance with Ohm’s law (voltage = current resistance), skin impedances under the cathode, anode and ground electrode were systematically measured and kept less than 20 kX by gently abrading the skin and wiping it with alcohol. The hand temperature was maintained above 30 C. The iMAX was the minimum stimulus intensity to elicit a maximal compound muscle action potential (CMAP) amplitude. The motor threshold (minimum intensity required to evoke a motor response of at least 100 mV of amplitude) was first measured. Then, the iMAX determination was a 3-step procedure. Firstly, the stimulus intensity was gradually and manually (about

Correlations between MUNIX and adapted multiple point stimulation MUNE methods

OBJECTIVEnThe aim of this study was to evaluate how the motor unit number index (MUNIX) is related to the adapted multiple point stimulation (AMPS) technique.nnnMETHODSnMUNIX and AMPS technique were prospectively performed on thenar muscles in 20 consecutive patients referred to our neurophysiological laboratory with the clinical diagnosis of a possible motoneurone disorder (MND). The clinical and paraclinical assessment confirmed the diagnosis of MND in 13 out of 20 patients, amyotrophic lateral sclerosis (ALS) in 9 (with MND group). In the other 7 patients, there were neither evidence of MND, nor of any peripheral nervous system disease (without MND group).nnnRESULTSnAMPS and MUNIX data were significantly (pu202f<u202f0.001) lower in patients with MND than in patients without MND. There was a strong significant positive linear correlation between AMPS and MUNIX values (nu202f=u202f20; Ru202f=u202f0.83; pu202f<u202f0.01).nnnCONCLUSIONnBoth MUNIX and AMPS methods could serve as a reliable marker to document the motor unit loss.nnnSIGNIFICANCEnThe present paper constitutes one more clue of MUNIX reliability.

Nerf interosseux antébrachial postérieur : élaboration de normes de laboratoire

Le syndrome du nerf interosseux antebrachial posterieur (NIAP), decrit pour la premiere fois par Agnew en 1863 [1] , consiste en une neuropathie motrice pure du NIAP au niveau du coude. Le tableau clinique est caracterise par une faiblesse des muscles extenseurs des doigts et abducteur du pouce. Le site de compression le plus souvent reconnu est l’arcade proximale du chef superficiel du muscle supinateur, decrite en 1908xa0par Frohse et Frankel [2] . En 1996, Seror decrit une technique electrophysiologique originale d’evaluation de la conduction du NIAP, permettant d’evaluer de facon sensible, specifique et reproductible sa conduction afin d’identifier la neuropathie du NIAP [3] . L’objectif de ce travail est l’elaboration des normes de laboratoire sur la difference de latence entre la reponse distale motrice du muscle extensor ulnaris carpi (EUC) et du muscle brachioradialis (BR) (LDM EUC-BR) apres stimulation du nerf radial au bras et la comparaison droite/gauche de ce parametre (D/G d). Nous avons realise des enregistrements de surface des reponses distales motrices de l’EUC (active au milieu de l’avant-brasxa0; reference sur la styloide cubitale) et du BR (active a 1xa0cm sous le pli du coudexa0; reference sur la styloide cubitale) evoquees apres stimulation percutanee du nerf radial au bras. Dans notre echantillon de 30xa0volontaires sains (âgexa0: 40xa0±xa016xa0ansxa0; taille 168xa0±xa09,8xa0cm), nous avons enregistre les resultats suivantsxa0: LDM EUC-BR droitxa0: 1,0xa0±xa00,32xa0ms, gauchexa0: 1,0xa0±xa00,31xa0ms, D/G dxa0: 0,2xa0±xa00,18. Nous avons fixe la limite superieure de la normale a la valeur moyennexa0+xa01,65xa0ecart-type pour atteindre une valeur de risque d’erreur egale a 5xa0%. Notre travail a permis d’etablir une valeur seuil de 1,5xa0ms pour la LDM EUC-BR tant a gauche qu’a droite et de 0,5xa0ms concernant la D/G d.