Reversible right vagal neuropathy

Abstract

REVERSIBLE RIGHT VAGAL NEUROPATHYVagus nerve efferent fibers carry the parasympathetic innervation to the heart. The right and left vagal nerve innervation to the heart is believed to be asymmetric, with the right vagal nerve providing most of the parasympathetic innervation to the atria and sinoatrial (SA) node. The left vagal nerve carries parasympathetic innervation to the ventricles. This anatomic and physiologic asymmetry has been studied in animals 1 but not as extensively in humans. Cardiovascular parasympathetic function can be assessed noninvasively by measuring the heart rate variability in response to deep breathing (heart rate deep breathing range [HR DB ]) or heart rate changes during the Valsalva maneuver (Valsalva ratio [VR]). 2 We describe a case of transient right vagal dysfunction and corresponding changes in the cardiovagal function in a patient with a right jugular foramen schwannoma. This report provides additional physiologic data to support the notion that cardiovagal innervation of the SA node comes from right vagus nerve.Case report. A 37-year-old man presented with a history of 3 episodes of syncope over the past 10 years. Results of an extensive cardiac workup were normal. He also noticed occasional difficulty swallowing liquids for the past 2-3 years. Neurologic examination revealed right gaze nystagmus and slight tongue deviation to the right. Results of the rest of the cranial nerve, motor, and sensory examinations were normal. A MRI brain scan revealed an irregularly enhancing mass in the right cerebellopontine and cerebellomedullary cisterns, causing mass effect on the brainstem and a 5-mm shift and distortion of the fourth ventricle without hydrocephalus (figure 1, A and B).As part of evaluation for unexplained syncope, an autonomic reflex screen 3 was performed. Cardiovagal heart rate responses to deep breathing and the Valsalva maneuver were normal ( figure 1, C and D). Beat-to-beat blood pressure changes during the Valsalva maneuver and head-up tilt were normal, indicating normal sympathetic vasomotor reflexes. Preoperative laryngoscopy revealed normal vocal cord movement. The patient went on to have a suboccipital craniotomy and resection of the jugular foramen tumor, which proved to be a schwannoma (figure e-1 on the Neurology ® Web site at www.neurology.org).Immediately after surgery, the patient frequently aspirated when swallowing thicker liquids and required a temporary gastrostomy. His voice became hypophonic and hoarse. Repeat laryngoscopy revealed complete paralysis of the right vocal cord. He also developed unexplained persistent tachycardia with a resting heart rate in the range of 110 -120 beats/min. Repeat autonomic testing revealed a profoundly impaired heart rate response to deep breathing and the Valsalva maneuver (figure 1, E and F) with normal sympathetic vasomotor function. Over the next 4 months, speech and swallowing function gradually improved and tachycardia resolved. Autonomic testing showed normalization of cardiovagal function (figure 1, G and H).Disc...

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