Case: You’re seeing a 64-year-old male with a three-month history of cough. What is your broad differential?

Definition of chronic cough: lasting more than 8 weeks (acute cough is less than 3 weeks, and sub-acute cough is 3-8 weeks) (1,2). 

Diagnostic approach: chronic cough has a long list of differential diagnoses. Using the systems framework is one way to help organize your differential list.

BOTTOM LINE: CHRONIC COUGH IS DEFINED AS LASTING MORE THAN 8 WEEKS. KNOW YOUR COMMON DIFFERENTIAL DIAGNOSES.

Red flags: weight loss, drenching night sweats, hemoptysis (rule out malignancy/tuberculosis), foreign body aspiration (requires urgent bronchoscopy) (2).

Back to the case: He describes the cough as dry and hacking, triggered by perfumes and smoking. He reports a 15 pack per day smoking history. His past medical history is significant for allergic rhinitis (allergies to dust mites and ragweed) for which he uses an intranasal steroid spray once daily. He doesn’t take any other medication. He denies weight loss, drenching night sweats, hemoptysis, recent travel, or sick contacts. Pertinent positive exam findings include wheezes heard at bilateral lower lung bases. What remains on your differential and how will you rule in, or rule out these diagnoses? Would you consider any diagnostic imaging at this point?

Role for Imaging

Chest x-ray: initial work up for chronic cough should include a chest x-ray to exclude mass, consolidation, interstitial lung disease, hilar lymphadenopathy, evidence of emphysema (2,3), pneumonia, bronchiolitis, and sarcoidosis (5). If you have a high index of suspicion for malignancy, keep in mind up to 26% of the lung parenchyma may not be adequately visualized on chest x-ray (5), making it less sensitive and specific compared with a CT. A normal chest x-ray does not rule out interstitial lung disease (4).

CT thorax: should be considered if there is suspicion for malignancy, or for ruling out other causes of chronic cough that are not as readily detected with chest x-ray (if suggestive from the history). CT is more sensitive and specific for ruling out malignancy, hilar and mediastinal lymphadenopathy, bronchiectasis, and interstitial lung disease (4,5).

CT thorax can also be considered after ruling out (and/or treating) common causes of cough (6). However, controversy on this topic exists. Choosing wisely recommends against ordering CT for patients with chronic cough who are at low risk for lung cancer (6). It has been suggested that performing routine CT may not be warranted for chronic cough patients with normal chest x-ray (7).

BOTTOM LINE: ORDER A CHEST X-RAY AS PART OF YOUR INITIAL WORK UP FOR CHRONIC COUGH.

Back to the case: Without any red flags, it is reasonable to evaluate for common causes of chronic cough first and causes that are suggestive from your exam. In this case, you might consider his allergic rhinitis as a contributing factor, but you would also want to consider COPD (smoking history) and asthma (history of atopy). His history of smoking should also alert you to the possibility of cancer, however no obvious b-symptoms are currently present. In this case, ordering spirometry and a chest x-ray are very reasonable initial steps (2). One may also consider ensuring his allergic rhinitis treatment is optimized. If your initial work-up does not land you with a confident diagnosis, additional diagnostic imaging and/or referral to a specialist is warranted. 

Key Take Home Points:

• Rule out red flags of chronic cough that require immediate management. If none are present, ordering a chest x-ray is reasonable to include in your initial work-up, recognizing it has poor sensitivity and specificity for certain diseases.

• Consider a CT if you have a high index of suspicion for ruling out less common causes of chronic cough or if you are concerned about malignancy.

References/readings:

1. British Medical Journal. Assessment of Chronic Cough. 2023. Available from https://bestpractice.bmj.com/topics/en-gb/69

2. Smith JA, Woodcock A. Chronic Cough. The New England journal of medicine. 2016;375(16):1544-51.

3. Satia I, Wahab M, Kum E, Kim H, Lin P, Kaplan A, et al. Chronic cough: Investigations, management, current and future treatments. Canadian journal of respiratory, critical care, and sleep medicine. 2021;5(6):404-16.

4. Canadian Association of Radiologists. Canada. 2021-2022 [2022; June 25, 2023]. Available from: https://car.ca/patient-care/referral-guidelines/

5. Barraclough K. Chronic cough in adults. BMJ British medical journal (International ed). 2009;338(7705):1267-9.

6. Gupta S, Goodridge D, Pakhalé S, McIntyre K, Pendharkar SR. Choosing wisely: The Canadian Thoracic Society's list of six things that physicians and patients should question. Canadian journal of respiratory, critical care, and sleep medicine. 2017;1(2):54-61.

7. An J, Lee J-H, Yoo Y, Kwon H-S, Lee J-S, Lee SW, et al. Chest computed tomography scan utilization and diagnostic outcomes in chronic cough patients with normal chest X-rays: analysis of routinely collected data of a tertiary academic hospital. Journal of thoracic disease. 2023;15(4):2324-32.

Other resources: Irwin RS, Baumann MH, Bolser DC, Boulet L-P, Braman SS, Brightling CE, et al. Diagnosis and management of cough executive summary: ACCP evidence-based clinical practice guidelines. Chest. 2006;129(1 Suppl):1S-23S.