Needle electromyography does not meaningfully impact findings in MR-neurography/-myography

Introduction: Magnetic resonance neurography (MRN) and myography (MRM) are emerging imaging methods for detecting diseases of the peripheral nerve system (PNS). Most patients with PNS diseases also undergo needle electromyography (EMG). This study examined whether EMG led to lesions that were detectable using MRN/MRM and whether these lesions could impair image interpretation. Methods: Ten patients who underwent clinically indicated EMG were recruited. MRN/MRM was performed before and 2-6 h after EMG, and if achievable, 2-3 days later. T2 signal intensity (SI) of the tibialis anterior muscle (TA) was quantified, and sizes and SI of the new lesions were measured. Visual rating was performed independently by three neuroradiologists. Results: T2 lesions at the site of needle insertion, defined as focal edema, were detectable in 9/10 patients. The mean edema size was 31.72 mm(2) (SD = 14.42 mm(2)) at the first follow-up. Susceptibility-weighted imaging lesions, defined as (micro) hematomas were detected in 5/10 patients (mean size, 23.85 mm(2) [SD = 12.59 mm(2)]). General muscle SI of the TA did not differ between pre- and post-EMG examinations. Lesions size was relatively small, and the readers described image interpretation as not impaired by these lesions. Discussion: This study showed that focal edema and hematomas frequently occurred after needle EMG and could be observed using MRN/MRM. As general muscle SI was not affected and image interpretation was not impaired, we concluded that needle EMG did not interfere with MRN/MRM.