Passage: The most common symptoms of COPD are sputum production, shortness of breath, and a productive cough. These symptoms are present for a prolonged period of time and typically worsen over time. It is unclear whether different types of COPD exist. While previously divided into emphysema and chronic bronchitis, emphysema is only a description of lung changes rather than a disease itself, and chronic bronchitis is simply a descriptor of symptoms that may or may not occur with COPD.

Question: What disease are professionals unclear if multiple iterations of exist?
COPD