[Asthma--a disease difficult to define. Patients can receive correct treatment by means of differential diagnosis criteria].

Asthma is a well defined disease in international consensus reports. However, in clinical praxis patients are often presenting asthma-like symptoms that are not explained by asthma and not by chronic obstructive pulmonary disease (COPD), the later being reported as the most common differential diagnosis. In an asthma and allergy clinic the most common differential diagnoses are asthma-like disorders, of which sensory hyperreactivity (SHR) can be identified by a capsaicin inhalation test. This review presents aspects on the investigation of adult patients with airway symptoms based on 20 years of clinical studies. It is pointed out that a careful asthma investigation strictly following diagnostic criteria is the first step. After this further diagnostic steps may be taken, especially as sensory mechanisms are often involved. Sensory hyperreactivity may also be present in patients with "classical" asthma sometimes explaining the lack of effect of asthma medication.