Electromyography (EMG) has shown limited value in confirming the diagnosis of ulnar nerve entrapment at the elbow when odds were previously high, but nerve conduction studies are showing normal values, according to a study recently published in Frontiers in Neurology. This does not negate the value of EMG in detecting concomitant conditions.
This prospective, observational, cross-sectional cohort study included 166 participants, whose mean age was 54.5±14.5 years (range 19-91) of whom 45% were men. All participants were referred for suspected ulnar nerve entrapment at the elbow in 2016. A standard neurophysical protocol of motor/sensory nerve conduction studies and EMG were used to examine 199 arms in the study population. Descriptive statistics were used in reporting all values.
Of the 123 arms with abnormal nerve conduction studies that received EMG (n=116), spontaneous muscle fiber activity abnormalities were identified in 23.3% (n=27). Nerve conduction studies indicated normal function in 38.2% (n=76) of all arms, with EMG finding no abnormalities in spontaneous muscle fiber activity. Of these 76 arms, 63.2% (n=48) were given additional diagnostics. Isolated abnormal motor unit action potentials were identified by EMG in 11.8% (n=9) of arms that showed normal nerve conduction studies, of which one received a clinical diagnosis of ulnar nerve entrapment at the elbow that was not detected by further nerve conduction studies, EMG, or ultrasound. Neuralgic amyotrophy had already been diagnosed in 1 arm, carpal tunnel syndrome in another, and additional diagnostics but no ulnar nerve entrapment in the other 6 arms.
The study researchers conclude, “[We] suggest a neurophysiological protocol exclusively for the confirmation of clinical [ulnar nerve entrapment at the elbow] in a high prior-odds diagnostic setting, in which EMG is not standard. EMG has limited value for diagnosis [of ulnar nerve entrapment at the elbow] if [nerve conduction studies] are normal, but is necessary for evaluating the differential diagnosis.”
Kurver A, Smolders J, Verhagen WIM, Meulstee J, Nijhuis FAP.The diagnostic sensitivity for ulnar neuropathy at the elbow is not increased by addition of needle EMG of ADM and FDI when nerve conduction studies are normal [published online March 11, 2019]. Front Neurol. doi: 10.3389/fneur.2019.00196