After exclusion of diverse pulmonary illnesses, the remaining explanations for chronic cough include medication with angiotensin-converting enzyme (ACE) inhibitor, gastroesophageal reflux disease (GERD), and post-nasal drip. Different clinics report shifting frequencies for both the causes of chronic cough and the success of treatment. However, after all evaluations, differential diagnosis still leaves a group of patients with unexplained cough. This unexplained cough is also known as chronic idiopathic cough (CIC), though there are widely varying opinions as to its existence. Among patients previously diagnosed with CIC, a subgroup has been identified with both upper and lower airway symptoms, including cough induced by odours and chemicals, and with increased cough sensitivity to inhaled capsaicin, which is known to stimulate the airway sensory nerves. A suggested explanation for this condition is a hyperreactivity of the sensory nerves of the entire airways, and hence the condition is known as sensory hyperreactivity (SHR). SHR affects more than 6% of the adult population in Sweden. It is a longstanding condition, and is clearly associated with significant social and psychological impacts.
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