Differential Diagnosis for Lingering Cough

Single Most Likely Diagnosis

• Postnasal Drip (Upper Airway Secretion Syndrome): This is often the most common cause of a chronic cough without fever, especially when it persists for more than a month. It occurs due to the dripping of secretions from the nose or sinuses down the back of the throat, irritating the cough reflex.

Other Likely Diagnoses

• Asthma: Cough can be a predominant symptom of asthma, especially in cases where wheezing is not prominent. Asthma can cause a chronic cough due to airway inflammation and hyperresponsiveness.
• Gastroesophageal Reflux Disease (GERD): Stomach acid reflux into the esophagus can irritate the throat and trigger a cough. This is more likely if the cough is worse after eating or at night.
• Chronic Bronchitis: Part of chronic obstructive pulmonary disease (COPD), chronic bronchitis involves inflammation of the bronchial tubes, leading to a persistent cough, often with mucus production.
• Allergic Rhinitis: Similar to postnasal drip, allergic reactions can cause chronic cough through the same mechanism of upper airway irritation.

Do Not Miss Diagnoses

• Lung Cancer: Although less common, lung cancer can present with a persistent cough as an early symptom. It's crucial to consider this, especially in smokers or those with a significant smoking history.
• Tuberculosis (TB): A chronic cough can be a symptom of pulmonary TB. Although less common in some regions, it's a critical diagnosis not to miss due to its public health implications and the need for specific treatment.
• Pneumonia (if initially mild or atypical): Some forms of pneumonia can present with a cough that lasts for weeks without significant fever, especially in older adults or those with compromised immune systems.
• Pulmonary Embolism: While typically presenting acutely, in some cases, a pulmonary embolism can cause a chronic cough, especially if it's recurrent or if there's associated pulmonary infarction.

Rare Diagnoses

• Cystic Fibrosis: More commonly diagnosed in childhood, but can be diagnosed later in life, presenting with chronic cough among other symptoms.
• Sarcoidosis: An autoimmune disease that can affect the lungs, causing a chronic cough among other symptoms like shortness of breath.
• Eosinophilic Pneumonia: A rare condition characterized by an accumulation of eosinophils in the lungs, which can cause a chronic cough.
• Histiocytosis X (Langerhans Cell Histiocytosis): A rare disorder that can cause a variety of pulmonary symptoms, including chronic cough.

Each of these diagnoses should be considered based on the patient's full clinical presentation, including history, physical examination, and diagnostic tests as appropriate.