Polyneuropathy occurs in 10% of cases of average severity and up to 75% of severe cases. Bulbar symptoms often occur in the first 2 weeks of illness like difficulty in swallowing and paresis of the palatal and ocular muscles. Respiratory dysfunction is the most severe symptom of toxicosis. Bulbar symptoms can progress to paralysis of the proximal and then distal skeletal muscles. However, most patients regain complete neurologic function.