Use sensory studies first when the differential includes root versus plexus disease, because SNAP preservation strongly supports a radiculopathy. Paraspinal denervation supports a root lesion, while multifocal limb-only abnormalities raise concern for plexopathy or more diffuse disease.

SNAPs are often normal in radiculopathy but abnormal in plexopathy; Paraspinal muscle denervation supports a root lesion; Lesions distal to the dorsal root ganglion affect sensory responses; ALS produces widespread denervation in multiple body regions; Electrodiagnostic localization depends on combining sensory, motor, and needle findings