Cough is also a common presenting symptom in primary care. Although cough can be part of a constellation of symptoms that leads to a specific diagnosis, it can also be the primary symptom in an undifferentiated patient. In these cases, the diagnosis must be obtained through a combination of careful history, physical examination, limited diagnostic testing, and often a trial of empiric therapy. Several elements of the history guide the initial differential diagnosis, especially a history of smoking, immunocompromise (HIV/AIDS or cancer chemotherapy), chronic pulmonary disease, medication use (ACE inhibitors), specific occupational exposures, or exposure to TB patients or TB-endemic areas.

Acute episodes of cough, defined as less than 3 weeks, are almost always caused by an acute infection (usually viral) or an acute exacerbation of chronic disease such as asthma or COPD, and the first rule should be to "do no harm" (primum non nocere) by treating conservatively and using time as a diagnostic test. Most episodes of acute cough caused by infection are viral in origin, mainly viral upper respiratory tract infections or acute bronchitis. Acute bacterial infections include sinusitis as well as bacterial overgrowth in exacerbations of chronic bronchitis or COPD. Fever, hemoptysis, or significant shortness of breath in association with cough indicates a chest radiograph or other immediate diagnostic evaluation. Frank hemoptysis can require urgent bronchoscopy for diagnosis and potentially for treatment (electrocoagulation of bleeding site). Without evidence of bacterial infection (clear evidence of sinusitis or pneumonia), previously healthy patients should generally be treated symptomatically without antibiotics, unless symptoms persist for more than 3 weeks.

Foreign body aspiration is a diagnostic consideration in children with either acute or chronic cough. Exacerbations of asthma, as well as infections by Bordetella pertussis (whooping cough) or Bordetella parapertussis, can lead to a persistent cough for as long as 3 to 8 weeks. Cough might indeed be the only symptom experienced by some patients with asthma (cough-variant asthma). In patients with underlying chronic bronchitis or COPD, antibiotics may be indicated during episodes of increased shortness of breath, wheezing, hypoxia, or limitations of activity if accompanied by a sudden change in sputum from thin and clear to thick or copious or yellow-green. Other subacute or chronic infections include bronchiectasis, which can manifest with a cough productive of mucopuru-lent, blood-tinged, or foul-smelling sputum. In children with chronic productive cough or recurrent pulmonary infections, cystic fibrosis must be considered. Survivors of premature birth with mechanical ventilation in neonatal intensive care may have chronic lung disease with acute exacerbations.

In adults, the most common causes of chronic cough in nonsmokers are postnasal drip, asthma, gastroesophageal reflux disease (GERD), and angiotensin-converting enzyme (ACE) inhibitors (Holmes and Fadden, 2004). Among smokers, chronic bronchitis, bronchiectasis, and bronchogenic carcinoma (lung cancer) must also be considered. Additional elements of the history can suggest other diagnoses. For example, occupational exposures can suggest specific diagnoses such as coal miner's lung or farmer's lung. Immigration from or travel to TB-endemic areas could suggest tuberculosis.

After the history and physical examination, a chest radiograph is the most valuable diagnostic test in evaluating the patient with chronic cough. Chest x-ray films can reveal infections (atypical pneumonia or TB), mass lesions (carcinoma), granulomatous disease (sarcoidosis), or evidence of occupational lung disease. Radiography can also reveal non-pulmonary causes of chronic cough, such as early CHF or pleural lesions. Office spirometry may also be performed to rule out obstructive lung disease.

In an otherwise healthy nonsmoker with chronic cough and a normal chest x-ray film, a trial of simple measures may be indicated. Persons being treated with an ACE inhibitor should be switched to alternative medication. Patients with occupational exposures should avoid the exposure or use protective equipment and should begin keeping a log to document the association of symptoms with days spent in workplace areas of exposure. Patients with signs of allergic rhinitis or postnasal drip may begin a simple trial of antihistamines. Patients with symptomatic GERD may begin taking a protein pump inhibitor (e.g., omeprazole) or H2 antagonist. In some cases, chronic cough is the only symptom of GERD, and a successful trial of these agents is diagnostic.

Follow-up is essential, and the primary care practitioner must document instructions to patients that those who do not respond to empiric therapy in 2 to 3 weeks need further diagnostic evaluation. If asthma is suspected and initial office spirometry revealed normal pulmonary function, a simple approach is to ask the patient to keep a log of symptoms and peak flow meter readings, with peak flow tested within 30 minutes of rising each morning. In patients with an abnormal chest radiograph or in smokers with a normal radiograph and a chronic cough that does not respond to empiric therapy, a HRCT scan or even bronchoscopy may be indicated to rule out malignancy. Additional causes of chronic cough that might require further testing include sarcoidosis, TB, and other gran-ulomatous or interstitial lung diseases, as well as pulmonary manifestations of autoimmune disease such as rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE).

Patients with HIV/AIDS or other compromise of the immune system deserve specific evaluation (see Chapter 17). HIV testing may be indicated in patients with any risk factors, because pulmonary symptoms can be the first manifestation of symptomatic HIV disease. In patients known to be HIV positive, tests in addition to chest radiography and HRCT could include gallium scan, PET, bronchoscopy with BAL for stains and cultures, PPD, and sputum testing for PCP.

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