Differential Diagnosis for Hypoxia in a 77-year-old Female Patient

Single Most Likely Diagnosis

• Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: Given the patient's age and the presence of possible mucous plugging or bronchiolitis on the CT chest, a COPD exacerbation is a plausible cause for hypoxia, even without a history of tobacco use, as other factors like environmental exposures or alpha-1 antitrypsin deficiency could be contributing factors.

Other Likely Diagnoses

• Pulmonary Embolism (PE) despite normal CT chest: Although the CT chest did not show evidence of PE, it is essential to consider that small PEs might not be visible on CT, especially if the study was not specifically a CT pulmonary angiogram (CTPA).
• Cardiac Causes: The slight elevation in troponin suggests some cardiac involvement, which could be contributing to hypoxia, possibly through heart failure or ischemia not evident on the EKG.
• Aspiration Pneumonia: Given the patient's Parkinson's disease, which can affect swallowing, aspiration pneumonia is a possibility, even if the CT does not show clear evidence of pneumonia, as it might be early or patchy.

Do Not Miss Diagnoses

• Pulmonary Venous Thromboembolism: Similar to PE, but originating from the pulmonary veins, which could be life-threatening and might not be immediately apparent on a non-contrast CT.
• Cardiac Tamponade: Although there's no mention of specific echocardiogram results, cardiac tamponade could cause hypoxia and slight troponin elevation without significant EKG changes initially.
• Aortic Dissection: This is a life-threatening condition that could cause hypoxia and slight cardiac enzyme elevation without clear EKG changes or chest pain, especially if the dissection involves the aortic arch or descending aorta.

Rare Diagnoses

• Pulmonary Alveolar Proteinosis: A rare condition characterized by the accumulation of surfactant-like protein and phospholipids in the alveoli, leading to hypoxia.
• Lymphangitic Carcinomatosis: Infiltration of the lymphatic vessels of the lung by metastatic cancer, which could cause hypoxia without significant findings on CT chest initially.
• Acute Interstitial Pneumonia (AIP): A rare, severe form of interstitial lung disease that can present with hypoxia and might not have distinctive features on CT chest early in the disease course.