About 12 days after a mild upper respiratory infection, a 12-year-old boy complains of weakness in his lower extremities. Over several days, the weakness progresses to include his trunk. On physical examination, he has the weakness described and no lower extremity deep tendon reflexes, muscle atrophy, or pain. Spinal fluid studies are notable for elevated protein only. Which of the following is the most likely diagnosis in this patient?

The paralysis of Guillain-Barre often occurs about 10 days after a nonspecific viral illness. Weakness is gradual over days or weeks, beginning in the lower extremities and progressing toward the trunk. Later, the upper limbs and the bulbar muscles can become involved. Involvement of the respiratory muscles is life-threatening. The syndrome seems to be caused by a demyelination in the motor nerves and, occasionally, the sensory nerves. Measurement of spinal fluid protein is helpful in the diagnosis; protein levels are increased to more than twice normal, while glucose and cell counts are normal. Hospitalization for observation is indicated. Treatment can consist of observation alone, intravenous immunoglobulin, steroids, or plasma-pheresis. Recovery is not always complete. Bell palsy usually follows a mild upper respiratory infection, resulting in the rapid development of weakness of the entire side of the face. Muscular dystrophy encompasses a number of entities that include weakness over months. Charcot-Marie-Tooth disease has a clinical onset including peroneal and intrinsic foot muscle atrophy, later extending to the intrinsic hand muscles and proximal legs. Werdnig-Hoffmann disease is an anterior horn disorder that presents either in utero (in about one-third of cases) or by the first 6 months of life with hypotonia, weakness, and delayed developmental motor milestones.