Correlation between electromyographic reflex and MR imaging examinations of the trigeminal nerve

Previous studies have shown that clinical localization of trigeminal nerve lesions is inaccurate as compared with MR imaging findings. The purpose of our study was to ascertain the added value of electromyographic (EMG) investigation of the trigeminal nerve reflexes for the improvement of lesion localization and for the preselection of patients for MR imaging.

We reviewed the EMG studies of the trigeminal reflexes and the MR imaging studies of 20 patients with unilateral symptoms and signs related to the trigeminal nerve (40 trigeminal nerves examined). The results of the two studies were compared to assess the value of EMG in predicting MR imaging outcome. Lesion localization as demonstrated by EMG was compared with localization at MR imaging. MR imaging was used as the standard of reference.

Eight (40%) of 20 patients had MR imaging findings related to presenting trigeminal symptoms, including five brain stem lesions and three peripheral lesions. Fourteen (70%) of 20 patients had EMG abnormalities related to presenting symptoms and signs. For brain stem lesions, lesion localization as shown by EMG corresponded well with MR imaging findings. EMG yielded a sensitivity of 100%, a specificity of 81%, a positive predictive value of 57%, and a negative predictive value of 100% in predicting MR imaging results. Interobserver agreement was good for both the EMG reflex and MR imaging examinations.

Our data suggest that EMG recordings of the trigeminal reflexes can be used to exclude structural lesions in patients with symptoms related to the trigeminal nerve. When a lesion is localized in the brain stem with EMG, a tailored MR imaging examination of this region may be sufficient.