Correlation between clinical phenotype and electromyographic parameters in amyotrophic lateral sclerosis

Introduction Even if electromyography (EMG) is routinely used to confirm the diagnosis of amyotrophic lateral sclerosis (ALS), few studies have analysed the correlation between electrophysiological parameters and clinical characteristics of ALS.

We assessed if the quantification of active denervation (AD) and chronic denervation (CD) provides clinicians with information about phenotype, disease progression and survival in ALS patients.

Methods We studied a cohort of 689 ALS patients recording the following parameters: age and site of onset, survival, MRC scale for muscle strength evaluation, burden of upper and lower motor signs as measured with specific scales (PUMNS and LMNS, respectively), ALSFRS-R, progression rate (ΔFS), MITOS and King’s Staging systems (KSS).

We performed EMG on 11 muscles, and calculated semiquantitative AD and CD scores for each limb, as well as for the bulbar and spinal regions.

Results We found a positive correlation between AD and CD scores with LMNS (respectively p =  4.4 × 10^–37 and p =  2.8 × 10^–45) and a negative correlation with MRC (respectively p =  4.5 × 10^–35 and p =  3.0 × 10^–35).

Furthermore, patients with higher spinal AD and CD scores had significantly lower ALSFRS-R scores, and higher KSS and MITOS stages.

Conversely, only AD was associated to higher ΔFS ( p =  1.0 × 10^–6) and shorter survival ( p =  1.1 × 10^–5).

Conclusion Our results confirmed that EMG examination represents not only a diagnostic instrument, but also a prognostic tool.

In this context, AD seems to be a reliable predictor of disease’s progression and survival while CD better describes functional disability.