<prompt> A 9-year-old boy presents with a several day history of progressive arm and leg weakness. He has been well except for an upper respiratory infection two weeks ago. The patient is ale and oriented. On repeated examination, the hea rate varies between 60 and 140 beatsminute and the blood pressure varies between 9060 and 14090 mm Hg. Respirations are shallow with a rate of 50minute. There is symmetric weakness of the face and all four extremities. Deep tendon reflexes are absent. Sensation is intact. The most likely diagnosis is:PolymyositisMyasthenia gravisTransverse myelitisGuillain-Barre syndrome  <response>: Progressive, symmetric motor weakness, areflexia, and autonomic instability, with mild or absent sensory signs, are typical features of Guillain-Barre syndrome. Frequently there is a history of infection often respiratory in the several weeks preceding clinical onset of the syndrome. Suppoive evidence for the diagnosis includes elevation of cerebrospinal fluid protein concentration with a mild 10 or fewer cellsmL mononuclear pleocytosis and slowing of nerve conduction velocities. Ref: Greenberg D.A., Aminoff M.J., Simon R.P. 2012. Chapter 10. Sensory Disorders. In D.A. Greenberg, M.J. Aminoff, R.P. Simon Eds, Clinical Neurology, 8e. 