12. Sensory nerve action potential ratios in acute inflammatory demyelinating polyneuropathies

Abstract

Introduction: Poliomyelitis involves the anterior horn cells experiencing peripheral denervation, which alters the motor unit (MU) properties. The noninvasive motor unit number index (MUNIX) method and the invasive macro electromyography (EMG) method are the two techniques used to evaluate the MU involvement. Objective: To compare the two techniques in characterizing the MU properties in prior polio. Method: MUNIX and macro EMG were performed in 50 tibial anterior (TA) muscles in 34 patients with the diagnosis of prior polio. Clinical assessment of force and muscle atrophy was performed. Results: The MUNIX and the relative macro EMG parameters showed a moderate correlation. The MUNIX for the prior polio group was decreased, compared to the age-matched control subjects by 24% on average. The elevation of themacromotor unit action potential (MUAP)amplitude for thepatientgroupcompared toagematchedcontrol subjects (relative macro MUAP amplitude) was 5.1 corresponding to an estimated loss of 61% of the neurons. However, there was a great scatter of the individual results in both groups. MUNIX and macro MUAP amplitudewere correlatedwith both force andmuscle atrophy. Conclusion: The MUNIX describes the number of MUs, regardless of the effectiveness of the reinnervation process, in contrast to the macro EMG which is reflecting the mechanism of collateral reinnervation. Pros and cons for the two techniques in characterizing the MU properties in prior polio are discussed.