Does respiratory onset als cause weakness in the arms or legs?

Sooner or later, ALS will cause weakness all over. Visit this site for information on this topic: https://www.mayoclinic.org/diseases-conditions/amyotrophic-lateral-sclerosis/symptoms-causes/syc-20354022

Typically, ALS results in need for respiratory support late in the illness. Presentation of pulmonary compromise initially, would suggest consideration of an alternative diagnosis