Electromyographic examination of ongoing denervation and reinnervation in anterior horn diseases

Introduction: Amyotrophic lateral sclerosis (ALS) is a relentlessly progressive and fatal disease that is characterized with degeneration of both upper and lower motor neurons. Lower motor neuron degeneration leads to denervation of target muscle that can only be reinnervated by collateral sprouting. These sprouts and newly settled neuromuscular junctions are immature that may lead crippled neuromuscular junction transmission. So showing the presence of neuromuscular junction transmission defect in a muscle by single fiber EMG may herald the presence of ongoing denervation and reinnervation. Objective: The aim of this study is to evaluate neuromuscular junction transmission defect and calculate peak number as an analogue to fiber density as a marker of reinnervation by using concentric needle electrode for the diagnosis of ALS. Method: Twelve patients who were diagnosed with definitive ALS according to Awaji criteria were enrolled. Quantitative Motor Unit Potential Analysis (Q-MUPA) was done in right extensor digitorum communis (EDC) muscle, Single Fiber Electromyography (SFEMG) was done both in right EDC and left frontalis muscles during voluntary contraction. Concentric needle electrode was used for both recordings. Results: In 11 of 12 patients (4 females, 8 males; aged between 42-80 years) Q-EMG of right EDC muscle was performed and overall 449 MUPs acquired and analyzed. Mean MUP duration of these MUPs were not diagnostically significant. However, the jitters calculated from EDC and frontalis muscles were high enough to prove the presence of neuromuscular junction transmission failure. Increased jitter was accompanied by high peak number that is a finding reflecting the presence of reinnervation. Conclusion: As it is necessary to show the presence of ongoing denervation and reinnervation both in extremity and trunk muscles for the diagnosis of widespread anterior horn involvement in ALS, measuring the jitter and counting the peak number with concentric needle electrode by means of SFEMG would be a reasonable approach. Keywords: Amyotrophic Lateral Sclerosis, Quantitative Motor Unit Potential Analysis, Single Fiber EMG, Fiber density