Diagnostic Utility Of Repetitive Nerve Stimulation Test Of The Trapezius Muscle In Amyotrophic Lateral Sclerosis (P4.113)

OBJECTIVE: To investigate the role of repetitive nerve stimulation (RNS) test in the diagnosis of amyotrophic lateral sclerosis (ALS). BACKGROUND: Early and definitive diagnosis of ALS is always a challenge to neurologists. Needle EMG is widely used for ALS diagnosis, although it causes significant pain. We previously documented high incidence of decremental response in RNS in ALS patients, especially in proximal muscles such as deltoid or trapezius muscles. Furthermore, spontaneous activities in the trapezius muscle were sufficiently sensitive and completely specific for ALS in comparison with cervical spondylosis. Cervical spondylotic amyotrophy (CSA) is a disorder commonly described in Japan, which is characterized by definite weakness and atrophy of proximal or distal upper limb muscles, with no or minimal sensory symptoms. Hence, this condition is an important differential diagnosis of ALS. DESIGN/METHODS: We prospectively enrolled ALS and CSA patients. RNS was conducted for 3 muscles, abductor pollicis brevis (APB), upper trapezius (Trap) and deltoid (Del). RESULTS: Enrolled subjects were 35 ALS and 28 CSA patients. The distribution of weakness in CSA patients were proximal in 12, distal in 13, and both proximal and distal in 3 patients. Abnormal decremental responses were observed in 30%, 34% and 63% of ALS patients for the APB, Trap and Del muscles, respectively. The incidence in CSA patients was 4%, 0% and 13%, respectively. CONCLUSIONS: Abnormal decremental response in RNS was a characteristic finding suggestive of ALS. Especially, decrement in the trapezius muscle was completely specific for ALS at least in comparison with CSA, although the sensitivity may not be extremely high. Less invasive RNS may be used as a substitute for needle EMG in order to document lower motor neuron involvement in the trapezius muscle, which is a key muscle in the differential diagnosis between ALS and CSA or other mimicking disorders. Disclosure: Dr. Hatanaka has nothing to disclose. Dr. Chiba has nothing to disclose. Dr. Ookuma has nothing to disclose. Dr. Kanbayashi has nothing to disclose. Dr. Kuwabara has nothing to disclose. Dr. Higashihara has nothing to disclose. Dr. Sonoo has nothing to disclose.