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Low intensity F-wave stimulation as a marker of excitability of lower motor neurons innervating hand muscles
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Introdução: O “split-hand syndrome” é um fenómeno de desenervação preferencial dos músculos laterais relativamente aos músculos mediais da mão, observado na Esclerose Lateral Amiotrófica (ELA). Alguns autores sugerem que este possa ser um fenómeno fisiológico evidenciado por processos de desenervação, e não um achado específico da ELA. O objetivo deste trabalho foi investigar diferenças fisiológicas entre os músculos envolvidos nesta “síndrome” analisando ondas-F obtidas com estímulos de baixa intensidade como marcador de excitabilidade dos neurónios motores espinhais. Métodos: Foram recrutados 27 voluntários saudáveis e registadas ondas-F a partir dos músculos Abductor Pollicis Brevis (APB), primeiro interósseo dorsal (FDI) e Abductor Digiti Minimi (ADM), utilizando 20 estímulos supramáximos e 20 estímulos de intensidade baixa, necessária para obter ondas-M com amplitude 10% do CMAP máximo. Os parâmetros das ondas-F avaliados incluíram latências, cronodispersão, persistência, amplitude, rácio amplitude F/CMAP e número de ondas-F “repeaters”. Também foram analisados índices “split-hand” baseados na persistência (SIFP) e rácio amplitude/CMAP (SIF/M) das ondas-F, recentemente descritos na literatura. Resultados: Comparando a estimulação de baixa intensidade com a estimulação supramáxima convencional, encontrámos valores de amplitude, persistência e SIFP menores e rácios amplitude F/CMAP e SIF/M maiores, mas nenhuma diferença significativa para as latências e cronodispersão das ondas-F. Comparando os três músculos, o ADM e o APB mostraram persistências e rácios amplitude F/CMAP superiores ao FDI e verificou-se um maior número de ondas-F “repeaters” no ADM. Foi encontrada uma correlação positiva entre o SIF/M e a idade. Discussão: Um número pequeno de estímulos de baixa intensidade parece adequado para estudar latências das ondas-F. Não ficou demonstrado um verdadeiro padrão “split-hand” fisiológico das propriedades dos neurónios motores espinhais que inervam os músculos da mão. O aumento do SIF/M com a idade pode estar relacionado com uma atrofia “split-hand like” associada ao envelhecimento.
Introduction: The “split-hand syndrome” refers to the phenomenon of preferential thenar muscle wasting with relative hypothenar muscle sparring, observed in Amyotrophic Lateral Sclerosis (ALS). Some authors have suggested this could be a normal physiological phenomenon enhanced by denervation processes, rather than a specific ALS finding. We aimed to investigate such physiological differences between involved hand muscles using low-intensity F-wave stimulation to assess lower motoneuronal excitability. Methods: We recruited 27 healthy volunteers. F-waves were recorded from the abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM) using 20 supramaximal stimuli followed by 20 stimuli at a low-intensity required to obtain M-waves with 10% amplitude of maximal CMAP. Evaluated F-wave parameters included latencies, chronodispersion, persistence, amplitude, F/CMAP amplitude ratios and number of F repeaters. Recently devised splithand indexes based on F-wave persistence (SIFP) and F/CMAP amplitude ratios (SIF/M) were also analyzed. Results: Comparing low-intensity stimulation with the standard supramaximal stimulation, we found lower F-wave amplitudes, persistence and SIFP, higher F/CMAP amplitude ratios and SIF/M, but no significant differences in F-wave latencies and chronodispersion. Comparing the three muscles, we found higher F-wave persistence and F/CMAP amplitude ratios when recording over the ADM and APB compared to the FDI. We also found a bigger number of F-wave repeaters in the ADM. SIF/M was positively correlated with age. Discussion: A small number of low-intensity stimuli seem to be appropriate to study F-wave latencies and chronodispersion. A true split-hand pattern of lower motoneuronal properties could not be found in healthy subjects. The increase of SIF/M with age can be an extension of the previously described “split-hand like” pattern of senile hand “abiotrophy”.
Introduction: The “split-hand syndrome” refers to the phenomenon of preferential thenar muscle wasting with relative hypothenar muscle sparring, observed in Amyotrophic Lateral Sclerosis (ALS). Some authors have suggested this could be a normal physiological phenomenon enhanced by denervation processes, rather than a specific ALS finding. We aimed to investigate such physiological differences between involved hand muscles using low-intensity F-wave stimulation to assess lower motoneuronal excitability. Methods: We recruited 27 healthy volunteers. F-waves were recorded from the abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM) using 20 supramaximal stimuli followed by 20 stimuli at a low-intensity required to obtain M-waves with 10% amplitude of maximal CMAP. Evaluated F-wave parameters included latencies, chronodispersion, persistence, amplitude, F/CMAP amplitude ratios and number of F repeaters. Recently devised splithand indexes based on F-wave persistence (SIFP) and F/CMAP amplitude ratios (SIF/M) were also analyzed. Results: Comparing low-intensity stimulation with the standard supramaximal stimulation, we found lower F-wave amplitudes, persistence and SIFP, higher F/CMAP amplitude ratios and SIF/M, but no significant differences in F-wave latencies and chronodispersion. Comparing the three muscles, we found higher F-wave persistence and F/CMAP amplitude ratios when recording over the ADM and APB compared to the FDI. We also found a bigger number of F-wave repeaters in the ADM. SIF/M was positively correlated with age. Discussion: A small number of low-intensity stimuli seem to be appropriate to study F-wave latencies and chronodispersion. A true split-hand pattern of lower motoneuronal properties could not be found in healthy subjects. The increase of SIF/M with age can be an extension of the previously described “split-hand like” pattern of senile hand “abiotrophy”.
Descrição
Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2023
Palavras-chave
Abductor digiti minimi Abductor pollicis brevis Primeiro interósseo dorsal Onda-F Split-hand Neurologia