Key distinguishing features of the most common diagnoses
|URTI||LRTI||Asthma||COPD||ACE Inhibitor Side Effect|
|Associated Shortness of Breath||No||Possible||Possible||Yes||No|
|Persistent or Recurrent Cough||No||No||Yes||Yes||Yes|
|On ACE Inhibitor||Possible||Possible||Possible||Possible||Yes|
Possible:FBC, ESR/CRP, spirometry, PEFR.
Small Print:Sputum, cardiac investigations, serum precipitins, hospital-based investigations such as CT scan and bronchoscopy.
- FBC: Hb may be reduced in malignancy and chronic illness; WCC raised in infections, eosinophils raised in allergic conditions.
- ESR/CRP: Raised in neoplasia, infective and inflammatory conditions.
- CXR: May show signs in a variety of the relevant differentials, such as LRTI, tumour and TB.
- Spirometry: May show characteristic patterns particularly in asthma, COPD and pulmonary fibrosis.
- Serial peak flow: May be helpful in diagnosis of asthma (guidance recommends testing fractional exhaled nitric oxide in suspected asthma but this may not be practical, or available).
- Sputum: May be useful in diagnosing TB and occasionally helps guide antibiotic treatment in LRTI or exacerbation of COPD.
- Cardiac investigations: Such as BNP or echocardiogram if LVF suspected.
- Serum precipitins: In suspected extrinsic allergic alveolitis.
- Hospital-based investigations: Further investigations such as CT scan or bronchoscopy may be required to clarify CXR abnormalities or pursue clinical suspicion.
- Explain to patients that it is not unusual for the cough of a simple URTI to go on for 3 weeks – this will reduce unnecessary re-attendances.
- Take a careful history of provoking factors in the case of persistent cough – this is more likely to reveal the diagnosis than is chest auscultation.
- Have a low threshold for arranging a CXR in the middle-aged and elderly smoker with a cough.
- ACE inhibitor-associated cough may come on many months – or even longer – after initiating treatment. It starts to improve within 1–4 weeks of stopping treatment but may take 3 months to settle completely.
- In a persistent cough with a normal CXR and no chest signs, think asthma, GORD and rhinitis – a therapeutic trial for each may be needed to clinch the diagnosis.
- Remember to ask about foreign travel. Atypical pneumonias are infrequent, and TB rare, but both can still present.
- Beware of persistent cough, weight loss and voice change in a smoker – arrange an X-ray to exclude malignancy.
- Night sweats with persistent cough suggest significant pathology such as TB or malignancy.
- Beware the patient on immunosuppressants – these drugs may alter the clinical picture, predispose to serious complications and in some cases (e.g. methotrexate) may be the cause of the cough itself.