Three weeks after an upper respiratory illness, a 25-year-old man develops weakness of his legs, which progresses over several days. On physical examination he has 4/5 strength in his arms but only 2/5 in the legs bilaterally. There is no sensory deficit, but knee and ankle reflexes cannot be elicited. During a 2-day observation period the weakness ascends, and he begins to notice increasing weakness of the hands. He notices mild tingling, but the sensory examination continues to be normal. The workup of this patient is most likely to show which of the following?

This patient presents with an acute symmetrical polyneuropathy characteristic of Guillain-Barre syndrome. This demyelinating process is often preceded by a viral illness or infection with Campylobacter jejuni. Characteristically, there is little sensory involvement; about 30% of patients require ventilatory assistance. Loss of deep tendon reflexes, especially in the lower extremities, is an important clue to the lower motor neuron involvement that characterizes GBS. Guillain-Barre syndrome is characterized by an elevated CSF protein with few, if any, white blood cells. EMG usually shows a demyelinating (not an axonal) process with nonuniform slowing and conduction block. A positive edrophonium test is characteristic of myasthenia gravis, but this patient's loss of tendon reflexes would not occur in MG. CK levels are normal, as there is no damage to muscle in this disease process. Arterial blood gases in Guillain-Barre syndrome might show a respiratory acidosis (not respiratory alkalosis) secondary to hypoventilation.