Vagus nerve ultrasound in a patient with amyotrophic lateral sclerosis

High-resolution ultrasound has become a valuable diagnostic tool in neuromuscular disorders. For many years, it has been utilized to evaluate entrapment neuropathies, but researchers have recently begun to investigate its diagnostic role in generalized neuromuscular diseases. The initial results regarding amyotrophic lateral sclerosis (ALS) are promising and suggest a potential role for ultrasound to identify disease biomarkers. Studies have focused so far on peripheral nerve and muscle ultrasound, and none have addressed cranial nerve ultrasonography in ALS. I report the use of ultrasonography to evaluate the vagus nerve in an ALS patient with mild bulbar symptoms. The study was approved by the local ethics committee, and informed consent was obtained from the patient. A 46-year-old man was referred to the electromyography laboratory for evaluation of a 1.5-year history of progressive weakness of the upper and lower limbs. He reported bulbar symptoms in the form of occasional choking, difficulty swallowing, and a harsh voice. He did not have sensory symptoms or bladder or bowel dysfunction. Cranial nerve examination yielded normal results. The thenar, hypothenar, and intrinsic hand and foot muscles were wasted on both sides. The lower limb muscles were mildly hypertonic, and muscle weakness was more evident distally in the upper and lower extremities. The tendon stretch reflexes of the lower limbs were exaggerated, and extensor plantar responses were noted on both sides. Sensory examination was normal. Motor conduction studies revealed low compound muscle action potential amplitudes in the median, ulnar, and tibial nerves on both sides. The distal motor latencies and conduction velocities were within normal ranges, and there was no evidence of focal conduction block. Sensory nerve conduction studies were normal. Needle electromyography revealed fibrillation potentials, positive sharp waves, and enlarged, polyphasic motor unit action potentials distributed across multiple myotomes. Fasciculation potentials were evident in the biceps brachii and triceps muscles. Fibrillation potentials were also detected in the thoracic paraspinal and sternocleidomastoid muscles. Based on the clinical and electrodiagnostic findings, the patient was diagnosed with clinically probable laboratory-supported ALS according to the revised El Escorial criteria. The vagus nerve was scanned bilaterally using an ultrasound system (Logiq P5; GE Healthcare, New York) and a 13-MHZ linear-array transducer. The transducer was positioned transversely in the lateral neck, and the nerve was identified inside the carotid sheath posterior to the internal jugular vein and carotid artery. The crosssectional area (CSA) was measured by tracing the nerve along the inner aspect of the hyperechoic rim. The vagus nerve CSA was 1 mm on both sides (Fig. 1), which was much smaller than the previously reported reference values obtained from healthy volunteers (means of 5 mm and 5.5 mm). This finding suggests there is vagus nerve atrophy in ALS, and it may reflect a type of degeneration that precedes the occurrence of overt bulbar manifestations. If the observed vagus nerve atrophy is further validated in a large-scale study, it may help establish sonographic criteria for diagnosis of ALS in conjunction with peripheral nerve and muscle ultrasound.