We aimed at establishing MUNIX repository of Poliomyelitis survivors, determining the rate of MUNIX decline longitudinally and comparing patient characteristics and disease parameters among polio subgroups.

Motor Unit Number index (MUNIX) is a non-invasive method that that involves utilizing the surface-recorded compound muscle action potential (CMAP) and electromyographic (EMG) interference pattern to compute the motor unit number index (MUNIX). This is the first study of this scale that applied MUNIX in Poliomyelitis (Polio).

 We performed longitudinal MUNIX measurements in 6 muscles in 41 Polio patients, 3-monthly, over 21 months period on the least affected side or the side with clinically not affected fourth limb. Detailed clinical data was also collected.

Of 41 (34 spinal and 7 spinobulbar) enrolled patients (M: F= 19:21), subgroup results varied.

Mean age (±SD) of patients was 62.1(±6.8) years. Mean disease duration at visit1 was 59.8(±6.6) years. 

Slight longitudinal decline in MUNIX values were recorded in 7 participants (17%). There were no differences between the later cohort and the rest of participants as regards to: demographics, polio onset age, gender, subtype, duration or post-polio syndrome (PPS) metrics (symptoms, onset age, duration and recovery type).

MUSIX values temporarily increased in 8 participants (19.5%) at time of muscle pain, returning to about 80-90% of baseline. Disease metrics were similar in this subgroup compared to other participants. 

This is the largest scale MUNIX study in Poliomyelitis. Our observation of the effect of pain on MUSIX needs further research perhaps using a combination of Neurophysiological techniques. 

Keywords: MUNIX, Poliomyelitis, Longitudinal study.