Q: What is the differential diagnosis for a cough that lasts longer than 8 weeks?
A: A key feature when evaluating a patient with cough is symptom duration. Acute cough lasts less than 3 weeks and is usually caused by respiratory tract infection. Cough lasting longer than 8 weeks is considered chronic and is most often due to postnasal drip, asthma, or gastroesophageal reflux disease.
Teaching topics from the New England Journal of Medicine - Vol. 358, No. 6, February 7, 2008