Phrenic nerve conduction studies (PNCSs) and respiratory muscle potential tests are used to assess respiratory muscle lesions in amyotrophic lateral sclerosis. This study aimed to determine normal values of PNC and respiratory muscle potentials in healthy Japanese school children. PNCS was performed by transcutaneous stimulation in the neck and recording diaphragmatic potentials from surface electrodes placed at the ipsilateral subcostal arch at the midclavicular line. Maximal expiratory and inspiratory potentials were measured using a multifunctional spirometer. In PNCS, amplitude, but not latency, changed with respiration. In the respiratory muscle potential test, the maximal inspiratory potential exhibited moderate correlation with both vital capacity and forced expiratory volume in 1 s. Using the reference values obtained in the current study, we plan to examine the potential utility of PNCS and respiratory muscle potential tests to assess respiratory muscle in school children.

Dropped head syndrome is commonly encountered on a daily clinical practice. Electromyography is often necessary for diagnosis because not only extrapyramidal disease but also neuromuscular disease may be the cause. In cases of suspicion that is caused by posterior neck weakness, repetitive nerve stimulation test, nerve conduction study, and needle electromyography were required to distinguish neuromuscular junction disorders, neurogenic disease, and myogenic disease. If abnormality cannot be found in the limbs, truncal electromyographic examination including the respiratory muscles may be required. The examiner should be familiar with electromyography of the trunk on a routine basis.