Approach to a cough (subacute and chronic): Clinical sciences

Coughing is a protective physiologic response that facilitates the clearing of secretions and debris from the airways of the lungs. The distinction between acute, subacute, and chronic cough is based on duration. An acute cough lasts less than three weeks, while a subacute cough lasts for three to eight weeks, and a chronic cough lasts more than eight weeks.

For subacute or chronic coughs, an abnormal chest X-ray is usually seen in atypical pneumonia, bronchiectasis, lung cancer, and interstitial lung disease. On the flip side, a normal chest X-ray is typically seen in gastroesophageal reflux disease, non-asthmatic eosinophilic bronchitis, upper airway cough syndrome, asthma, and chronic obstructive pulmonary disease.

Now, if your patient presents with a subacute or chronic cough, first perform a focused history and physical examination. Your patient will report a cough lasting at least three weeks and perhaps eight weeks or more, which might be accompanied by shortness of breath. They may also have a history of tobacco use, as well as known pulmonary conditions, like asthma or COPD. Additionally, the physical exam might reveal labored breathing and adventitious breath sounds such as wheezing or rales. With these clinical findings, diagnose subacute or chronic cough!

Here’s a high yield fact! One of the most common non-disease related causes of cough is ACE inhibitor-induced cough. Individuals who are taking ACE inhibitors for hypertension or heart disease can develop a dry and hacking cough that typically occurs in 1 to 2 weeks after starting the medication; but in some cases, it might occur after 6 months! This is likely due to the accumulation of bradykinin and it typically resolves within a few days of stopping the medication.

Alright, once you diagnose subacute or chronic cough, your next step is to obtain a chest X-ray! If your patient’s chest X-ray is abnormal, meaning there’s radiographic evidence of airway or lung involvement, your next step is to assess the underlying cause.

Let's look at all abnormal cases starting with atypical pneumonia! Along with a cough, your patient will typically report fever, chills, sore throat, and possibly headache. On physical exam, lung auscultation might reveal scattered rales and wheezes; and in some cases, you might even observe a rash! Finally, the chest X-ray will show bilateral patchy infiltrates, which confirms the diagnosis of atypical pneumonia!

Here’s a clinical pearl to keep in mind! Atypical pneumonia is caused by atypical bacteria, like Mycoplasma, Chlamydia, or Legionella. With these pathogens, clinical manifestations develop gradually, in contrast to typical pneumonia caused by Streptococcus pneumoniae, which is more rapid in onset.

Additionally, you can usually diagnose atypical pneumonia based on history and chest X-ray findings, but you could also consider ordering Chlamydia and Legionella urinary antigens, as well as Mycoplasma cold agglutinin testing to confirm the causative bacteria, to help you guide antibiotic management!

Now, let’s move on to bronchiectasis! These patients typically report copious sputum production. On physical exam, lung auscultation typically reveals crackles, rhonchi, and inspiratory wheezes. Chest X-ray usually shows tram-track opacities, which indicate dilated airways with thickened walls that run in parallel like a tram track. At this point, consider bronchiectasis, and order a chest CT!

If the chest CT reveals thickened bronchial walls and dilatation of the bronchial lumen, you can diagnose bronchiectasis! While bronchiectasis is a chronic condition, your patient may have occasional acute flare-ups, typically triggered by a respiratory infection, which will result in acute cough!

Okay, now let’s discuss lung cancer! In this case, your patient will typically report pleuritic chest pain, unintentional weight loss, and fatigue. In some cases, they might report hemoptysis. Additionally, the physical exam might reveal tachypnea and clubbing of the distal extremities; while the chest X-ray will show a lung nodule or mass, with or without pleural effusion.

At this point, consider lung cancer as a cause of chronic cough, and order a bronchoscopy with a biopsy of the mass or nodule. If the biopsy reveals malignant cells, you can diagnose lung cancer.

Finally, let’s take a look at interstitial lung disease! These patients will report shortness of breath on exertion, while the physical exam will reveal wheezing and diffuse inspiratory crackles on lung auscultation. You might also see finger clubbing, cyanosis, and low oxygen saturation.

The chest X-ray usually reveals reticular or nodular opacities. Next, order pulmonary function tests, which will show reduced diffusing capacity for carbon monoxide, sometimes in combination with a restrictive pattern on spirometry. At this point, consider interstitial lung disease, and order a high-resolution chest CT scan.