Asthma: Given the presence of scant expiratory wheezing, asthma is a highly plausible diagnosis. Asthma can present with variable symptoms, including wheezing, cough, shortness of breath, and chest tightness, often triggered by respiratory infections or allergens.

Chronic Obstructive Pulmonary Disease (COPD): Although COPD typically presents in older individuals with a history of smoking, it could be considered in a 40-year-old with a significant smoking history or exposure to harmful substances. Symptoms include chronic cough, sputum production, and shortness of breath.
Allergic Rhinitis: This condition can cause upper respiratory symptoms such as sneezing, runny or itchy nose, and nasal congestion, which might be accompanied by wheezing if there's associated asthma or if the allergic reaction affects the lower airways.
Acute Bronchitis: Usually follows a viral upper respiratory infection, characterized by a persistent cough, often with sputum production. Wheezing can be present, especially if there's an underlying respiratory condition.

Pneumonia: Although the patient does not have fever or chills, atypical pneumonia (caused by organisms like Mycoplasma pneumoniae) can present with mild symptoms, including wheezing. Missing this diagnosis could lead to severe consequences.
Pulmonary Embolism: While less common, pulmonary embolism can present with sudden onset of shortness of breath and wheezing, especially if the embolism is large. It's a life-threatening condition that requires immediate attention.
Foreign Body Aspiration: Although more typical in children, adults can also aspirate foreign bodies, leading to sudden onset of respiratory symptoms, including wheezing.

Vocal Cord Dysfunction: Can mimic asthma with symptoms of wheezing and shortness of breath but is due to abnormal vocal cord movement. It's often associated with stress, anxiety, or irritants.
Eosinophilic Pneumonia: A rare condition characterized by an accumulation of eosinophils in the lungs, which can cause respiratory symptoms, including wheezing. It might be related to medications, infections, or idiopathic causes.
Churg-Strauss Syndrome (Eosinophilic Granulomatosis with Polyangiitis): A rare autoimmune condition that can cause asthma-like symptoms, including wheezing, along with eosinophilia and vasculitis affecting multiple organ systems.