Onset of lower extremity paresthesias and weakness and flaccid paralysis with progression (hours to days) to trunk, arms, neck, and cranial nerves; also accompanied by fevers, muscle stiffness, and myalgias. Specific etiology is unknown; 50% of cases follow upper respiratory infections. Condition is also associated with bacterial, parasitic, and other viral infections; surgery; vaccines; insect bites; and leukemia and lymphoma. Degree of resolution is variable; plasma-pheresis is indicated in severe cases. Supportive ventilation may be required. Prognosis is better in children than in adults.