Clinical Reasoning: A 40-year-old woman presenting with distal leg weakness

A 40-year-old Caucasian woman reported 15 years of progressive lower leg and hand weakness. Weakness began asymmetrically in the legs. She had trouble standing on her toes and developed progressive bilateral foot drop, worse on the right. Over the years, she developed difficulty arising from low seats and climbing stairs. She began falling with her knees buckling bilaterally. She was a hairstylist, but stopped working about 2 years prior after the onset of weakness in her hands, including difficulty opening jars or using scissors. These symptoms progressed insidiously over the years without fluctuation.