Muscle Ultrasound Measures as Biomarkers of Upper Motor Neuron Function

Study Summary

Background: \- Primary lateral sclerosis (PLS) is a rare disease. It leads to weakness in the muscle of the arms, legs, and face. People with PLS develop muscle stiffness called spasticity. Researchers want to find a better way to measure this. They want to see if ultrasound, which uses sound waves to look at parts of the body, can measure spasticity and stiffness in muscles. Objective: \- To see if ultrasound can detect and measure muscle spasticity in people with PLS. Eligibility: * People ages 18 75 who have a diagnosis of PLS and are enrolled in protocol 01-N-0145. * Healthy volunteers ages 18 75. Design: * Participants with PLS will have 1 study visit. Healthy participants will have upto 5 visits. Each visit will be about 2 hours. * Participants will have tests of muscle strength. They will be examined. They will push their arms and legs against researchers in different positions. * Participants will have tests of muscle stiffness. Their arms and legs will be moved while they relax. * Participants will have a muscle ultrasound test. They will lie on a table. Gel will be placed on the skin over the muscles of the arms and legs. A probe, like a microphone, will be moved over the skin. Researchers will look at several muscles. * Participants should try to stay still during the ultrasound. It may be done several times and may be done by different examiners.