Prevalence and Clinical Associations of A-Waves in Routine Nerve Conduction Studies: A Retrospective Analysis.

Introduction: A-waves are late responses following the motor response during motor nerve conduction studies (NCSs) observed in healthy people and patients with neurological disorders. The aim was to define the prevalence and clinical associations of A-waves in a cohort referred to the electrophysiology laboratory for routine NCSs. Methods: This is a retrospective study. We analyzed the medical and electrophysiological data of 456 patients admitted to our neurophysiology laboratory between January 2022 and December 2022, evaluated by a single examiner (A.G.), and had F-wave studies. Results: We included 1197 nerves from 404 patients in this cohort. The most common diagnosis was entrapment neuropathy, followed by polyneuropathy, radiculopathy, motor neuron disease, myopathy, and other diagnoses. Twenty-five patients had multiple conditions, and 185 patients had no abnormal NCSs. The A-waves were seen in 42.2% of individuals with otherwise normal NCSs. The A-waves were most commonly found in patients with polyneuropathies, followed by motor neuron disorders, radiculopathy, and myopathy. However, the majority of polyneuropathy patients had multiple A-waves. A-waves were detected in 78 of 185 normal NCSs; 7 % had multiple A-waves. Multiple and single A-waves were more commonly recorded in the tibial nerves. The A-waves were more frequently observed in older subjects. Conclusions: Other than multiple A-waves, A-waves were commonly seen in subjects with normal NCSs. As far as we know, this is the first study reporting the presence of A-waves in myopathy and neuromuscular junction disorders. Still, this finding should be interpreted cautiously given the limited clinical data available.