A differential comes up short in a patient with shortness of breath.

Chronic obstructive pulmonary disease (COPD) exacerbation and allergic bronchopulmonary aspergillosis (ABPA), in spite of sharing common features such as airway inflammation, airflow obstruction, and mucus hypersecretion, differ significantly from each other. We report a case of ABPA that was unsuccessfully treated as a COPD exacerbation. The history of non-exertional progressive dyspnea, absence of a symptom-free interval, and hemoptysis combined with a minimal, distant smoking history and prior employment at a fertilizer plant favor a diagnosis other than COPD exacerbation. The patient's disease progression and delay in diagnosis testify to the sway of cognitive biases. This case serves as a reminder that generating a thorough differential diagnosis early in a patient's care prevents misdiagnoses and hastens the initiation of definitive therapy.