Pulmonary Embolism (PE): A leading cause of acute onset of symptoms such as shortness of breath, chest pain, and minimal pleural effusion, especially in patients with risk factors for thromboembolism.

Pneumonia: Can present with minimal pleural effusion, especially if caught early or if the pneumonia is not severe. Bacterial, viral, or fungal etiologies are possible.
Acute Coronary Syndrome (ACS): Although more commonly associated with cardiac symptoms, ACS can lead to minimal pleural effusion, particularly if there is associated heart failure or pulmonary edema.
Pulmonary Hypertension: Can cause right heart strain leading to minimal pleural effusion, among other symptoms like dyspnea and fatigue.

Aortic Dissection: A life-threatening condition that may present with chest pain, shortness of breath, and a small pleural effusion due to leakage of blood into the pleural space. Prompt diagnosis is crucial.
Pneumothorax: Especially if traumatic, can present with minimal symptoms and a small pleural effusion, but requires immediate intervention to prevent further complications.
Malignancy: Metastatic disease to the lung or pleura can cause a small pleural effusion. Although less common as an initial presentation, it's critical not to miss due to its implications for treatment and prognosis.

Lymphangitic Carcinomatosis: A rare condition where metastatic cancer infiltrates the lymphatic vessels of the lung, potentially causing minimal pleural effusion among other respiratory symptoms.
Eosinophilic Pneumonia: A group of diseases characterized by an accumulation of eosinophils in the lungs, which can lead to a small pleural effusion and other pulmonary symptoms.
Sarcoidosis: Although more commonly associated with hilar lymphadenopathy, sarcoidosis can rarely present with a minimal pleural effusion as part of its pulmonary involvement.