Application Value of the Motor Unit Number Index in Patients With Kennedy Disease.

Dongsheng Fan,Yingsheng Xu,Xiaoxuan Liu,Shuo Zhang,Yongmei Luo,Xin Yang

doi:10.3389/fneur.2021.705816

Abstract

The aim of this study was to evaluate the usefulness of the motor unit number index (MUNIX) technique in Kennedy disease (KD) and test the correlation between the MUNIX and other clinical parameters. The MUNIX values of the bilateral deltoid, abductor digiti minimi (ADM), quadriceps femoris (QF), and tibialis anterior (TA) were determined and compared with the course of the disease. The MUNIX sum score was calculated by adding the MUNIX values of these 8 muscles. Disability was evaluated using the spinal and bulbar muscular atrophy functional rating scale (SBMAFRS). The MUNIX scores of patients with KD were negatively correlated with the course of the disease (p < 0.05), whereas their motor unit size index (MUSIX) scores were positively correlated with the course the of disease (p < 0.05). MUNIX sum scores were correlated with SBMAFRS scores (r = 0.714, p < 0.05). MUNIX was more sensitive than compound muscle action potentials or muscle strength as an indicator of neuron loss and axonal collateral reinnervation. The MUNIX sum score is an objective and a reliable indicator of disease progression, and it is a potential choice for therapeutic clinical trials. The MUNIX can assess the functional loss of motor axons and is correlated with disability. The MUNIX sum score may be especially suitable as an objective parameter.

Highlights

Kennedy’s disease (KD), known as X-linked recessive spinal and bulbar muscular atrophy (X-SBMA), is a rare, late-onset, slowly progressive X-linked recessive neuromuscular disease with an incidence of ∼1/400,000 [1]
We explored the feasibility and usefulness of the motor unit number index (MUNIX) technique in Kennedy disease (KD)
Our findings demonstrated that the MUNIX values of the deltoid, abductor digiti minimi (ADM), quadriceps femoris (QF), and tibialis anterior (TA) muscles were significantly lower in patients with KD than in control subjects due to motor neuron loss

Summary

Introduction

Kennedy’s disease (KD), known as X-linked recessive spinal and bulbar muscular atrophy (X-SBMA), is a rare, late-onset, slowly progressive X-linked recessive neuromuscular disease with an incidence of ∼1/400,000 [1]. The clinical manifestation is characterized by weakness and atrophy localized proximally in the limbs, bulbar involvement, and abnormalities of the sensory nerves and endocrine system [2]. KD may have similar symptoms to amyotrophic lateral sclerosis (ALS), including morbidity due to weakness, but KD has a greater zchronic progression rate with a fairly normal lifespan. A good biomarker is needed to reflect both neuron loss and collateral reinnervation. Neither muscle strength nor Application of MUNX in KD the amplitude of compound muscle action potentials (CMAPs) directly reflects the change in motor neuron loss in KD, probably due to chronic compensatory collateral sprouting [6, 7]

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Conclusion