Differential Diagnosis for 78-year-old Female with Recent Illness

Single Most Likely Diagnosis

• Acute Bronchitis: Given the patient's symptoms of a bad cough that started as a regular cough and worsened over two weeks, with phlegm sensation in the chest, acute bronchitis is a likely diagnosis. The recent travel to Florida could have exposed her to new pathogens, contributing to the illness.

Other Likely Diagnoses

• Pneumonia: The patient's symptoms of cough and phlegm sensation in the chest, especially with a history of malignant neoplasm of the lung, make pneumonia a plausible diagnosis. The fact that the cough worsened over time also supports this possibility.
• Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: Although the patient's history of lung malignancy is noted, COPD could be a comorbidity, and the current symptoms could represent an exacerbation, especially if she has a history of smoking or other risk factors not mentioned.
• Asthma: Less likely but possible, especially if the patient has allergies (considering the use of azelastine nasal spray) and the cough is related to allergic reactions or asthma exacerbation.

Do Not Miss Diagnoses

• Lung Metastasis or Recurrence: Given the patient's history of malignant neoplasm of the lung, it is crucial not to miss a potential recurrence or metastasis, which could present with similar respiratory symptoms.
• Pulmonary Embolism (PE): Although less common, PE is a life-threatening condition that can present with cough and chest discomfort, especially in patients with a history of malignancy, which increases the risk of thromboembolic events.
• Tuberculosis (TB): While less likely, TB can present with chronic cough and should be considered, especially if the patient was exposed to TB during her travel or has risk factors not mentioned.

Rare Diagnoses

• Bronchiectasis: A condition characterized by damaged, widened airways, which could result from recurrent infections or other conditions. It's less likely but could explain chronic cough and phlegm production.
• Sarcoidosis: An autoimmune disease that can affect the lungs, among other organs, and present with cough and respiratory symptoms. It's rare and would require further investigation for diagnosis.

Next Steps in Treatment and Diagnosis

1. Complete Physical Examination: Including lung auscultation to check for abnormal sounds.
2. Imaging: Chest X-ray or CT scan to evaluate the lungs for signs of infection, malignancy, or other abnormalities.
3. Laboratory Tests: Complete blood count (CBC), blood cultures if fever is present, and possibly sputum analysis for culture or cytology.
4. Pulmonary Function Tests (PFTs): If COPD or asthma is suspected.
5. Consider Consultation: With a pulmonologist or oncologist given the patient's history of lung malignancy.

These steps will help narrow down the differential diagnosis and guide appropriate treatment.