Phrenic Nerve Conduction Studies Are Enhanced by Simultaneous Visualization of the Diaphragm with Ultrasound (P01.198)

Abstract

Objective: To determine if diaphragmatic ultrasound (DU) complements phrenic nerve conduction studies (PNCS) in the evaluation of phrenic neuropathy. Background PNCS are often performed to evaluate phrenic nerve function. However, PNCS can be technically difficult, and associated with false positives and negatives. Design/Methods: PNCS with simultaneous DU was performed in 10 patients (mean age: 42; range: 1-71) referred for phrenic neuropathy. The phrenic nerve was supramaximally stimulated in the neck bilaterally at end-expiration. Both the diaphragmatic compound muscle action potential (CMAP, recording electrode above xiphoid, reference electrode inferolaterally over ipsilateral costal margin) and the evoked diaphragmatic muscle twitch (visualized with percutaneous ultrasound over the lateral chest wall), were recorded. In addition, diaphragmatic movement during spontaneous respiration was visualized with DU and recorded. Correlations were sought between PNCS and DU data. Results: PNCS and DU data were concordant in 17/20 studies, documenting phrenic neuropathy in 8 patients including 2 with a very low amplitude CMAP and twitch. Of 3 discordant studies, 1 had an unevocable diaphragmatic CMAP and twitch but normal diaphragm movement with respiration (false positive), 1 had a low amplitude CMAP but normal diaphragmatic twitch and movement with respiration (false positive), and 1 had a normal CMAP but low amplitude diaphragmatic twitch and movement with respiration (false negative). Conclusions: Unlike other motor NCS, PNCS are limited by inability to visualize the evoked muscle twitch and target muscle during spontaneous movement. Addition of DU to PNCS provides this information, and enhances the diagnostic accuracy of PNCS, specifically by: 1) confirming partial phrenic neuropathy when CMAPs are low amplitude by demonstrating diminished but evocable diaphragmatic twitch and spontaneous movement, 2) reducing false positives when PNCS are technically challenging (e.g., CMAPs unevocable but diaphragmatic spontaneous movement normal), 3) reducing false negatives when CMAPs are of low-normal amplitude but diaphragmatic movement is reduced. Disclosure: Dr. Johnson has nothing to disclose. Dr. Patrick has nothing to disclose. Dr. Downs has nothing to disclose. Dr. Dogra has received personal compensation in an editorial capacity for Ultrasound Clinics. Dr. Logigian has received personal compensation for activities with Genzyme Corporation as a consultant.