Incidental complex repetitive discharges on needle electromyography

Complex repetitive discharges (CRDs) are spontaneous electromyography (EMG) waveforms often associated with chronic neurogenic or myopathic diseases, but incidentally identified CRDs have also been described. In this study we describe the distribution and possible significance of incidentally seen CRDs in otherwise normal electrodiagnostic studies.

A retrospective chart review was performed of all patients with CRDs incidentally documented on otherwise normal electrodiagnostic studies at Mayo Clinic from January 2013 through December 2020. Each patient's clinical symptoms, referral reason, electrodiagnostic report, and imaging studies were analyzed using descriptive statistics.

Ninety-four patients (86 females; mean age, 62 years; range, 20 to 86 years) and 107 CRDs were studied. The most common neuromuscular reasons for electrodiagnostic referrals included radiculopathy, peripheral neuropathy, and myopathy. Mean symptom duration was 43 months (range, 1 to 312 months). Eighty-five patients had a CRD identified in one muscle (range, in all patients, one to five muscles). CRDs were identified most frequently in tensor fasciae latae (n = 21), biceps brachii (n = 16), and gluteus maximus (n = 9). Of the 58 patients in whom imaging was available, 46 (79%) had abnormalities that corresponded to the myotome in which the CRDs were visualized, most commonly L5 (n = 19) and C6 (n = 12). Of these 46 patients, 28 (61%) were referred for radicular or limb pain.

CRDs can be incidentally noted on otherwise normal electrodiagnostic studies, most commonly in L5 and C6 myotomes. The mechanism of CRDs in the absence of electrodiagnostic features of axon loss or remodeling is unknown.