Sunday, April 27, 2008

Cough: differential diagnosis and treatments

The demographics of cough are impressive. Cough is the second most common reason for all office visits to physicians. In 1992, this was 24,997,000 visits or 3.6% of all visits. Cough is the most common reason for acute office visits to physicians. 76% of patients with cough are seen within 6 days of onset.

After the vagus nerve is stimulated, a cough may be reflexively generated. The goal of coughing is to remove the stimulus. Initially, the body creates a large pressure differential between the distal airways and mouth. Next, the cough produces air flow with a high velocity and strong shearing force.

Cough can be caused by many disorders, which usually stimulate the vagus nerve. The 3 most common causes are rhinitis or sinusitis with post-nasal drip, bronchial asthma, and gastroesophageal reflux. Other causes include chronic bronchitis (smoke, fume), abnormal airways (bronchiectasis, growths, foreign bodies, compression), pulmonary infections like tuberculosis, infiltrative lung diseases, aspiration, psychologic, and medications (beta-blockers, ace-inhibitors).

The diagnostic evaluation should include a detailed history (the key !) and physical examination. The 2 most useful studies are a chest x-ray and spirometry. Other useful studies include sputum examination, methacholine challenge, blood tests, sinus x-rays, CT scan of the chest, gallium scan, gastroesophageal reflux studies, cardiac evaluation, and bronchoscopy.

When evaluating a patient with cough, do not forget to search for complications, such as vomiting, abdomenal wall pains, elevated blood pressure, syncope, hypoxia, bone fractures, muscle strains or tears, cartilage strains or tears of the neck, chest or back, pneumothorax, pneumomediasteinum, laryngitis, urine incontinence, and fatigue (physical, psychologic).

Ideally, treatment should be focused on the cause, not just suppression. Non-specific treatments work by 3 mechanisms. First, the cough reflex may be prevented by anesthetics (xylocaine, benzocaine, benzonatate). Second, the cough reflex may be suppressed by anti-tussives, such as over-the-counter dextromethorphan, over-the-counter diphenhydramine, or prescription anti-cholinergics (promethazine), or prescription opiates (codeine, hydrocodone). Finally, make productive coughing less difficult with demulcents to increase salivation (lozenges and sprays with menthol, honey) or expectorants to "loosen" the saliva (guaifenesin, water, steam). Specific treatments should also be prescribed to treat the underlying cause.

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