Bronchiolitis Obliterans: This condition is characterized by inflammation and obstruction of the small airways, which can lead to air trapping without significantly affecting spirometry results initially. The normal spirometry with significant air trapping is a hallmark of this condition in its early stages.

Cystic Fibrosis: Although cystic fibrosis often presents with abnormal spirometry due to chronic infections and bronchiectasis, early or mild cases might show significant air trapping with relatively preserved spirometry.
Bronchiectasis: Similar to cystic fibrosis, bronchiectasis can cause air trapping, especially if the disease is not widespread or if the patient is seen early in the disease process.
Small Airway Disease: Conditions affecting the small airways, such as respiratory bronchiolitis or follicular bronchiolitis, can lead to air trapping with minimal impact on spirometry.

Alpha-1 Antitrypsin Deficiency: This genetic disorder can lead to panacinar emphysema and significant air trapping, even with normal spirometry in early stages. Missing this diagnosis could lead to delayed treatment and significant morbidity.
Lymphangitic Carcinomatosis: Metastatic cancer to the lungs can cause air trapping due to lymphatic obstruction. Although less common, this diagnosis is critical due to its implications for treatment and prognosis.

Neuroendocrine Cell Hyperplasia of Infancy (NEHI): A rare condition seen in infants, characterized by airway obstruction and air trapping, with spirometry that may be normal or near-normal.
Follicular Bronchiolitis: An inflammatory condition affecting the bronchioles, which can cause air trapping. It is more commonly seen in immunocompromised patients or those with rheumatologic diseases.
Diffuse Panbronchiolitis: A rare condition characterized by chronic inflammation of the bronchioles, which can lead to air trapping and might have a relatively preserved spirometry in early stages.