Influence of comorbid conditions on asthma.

Various conditions such as rhinosinusitis, gastro-oesophageal reflux disease, psychological disturbances, chronic infections and obstructive sleep apnoea are often observed in asthmatic patients and may affect asthma control and outcomes. These comorbidities may change the asthma phenotype, be part of the same pathophysiological process, act as confounding factors in the diagnosis or assessment of control of asthma, and/or result from specific environmental exposures. The influences of these conditions on asthma are variable and for many of them still uncertain; nevertheless, they may alter asthma responses to current therapy. A systematic evaluation and an appropriate treatment of asthma-associated comorbid conditions should be part of asthma management, particularly for severe disease. With regard to clinical research, associated conditions may influence the results of trials and should be taken into account in the subjects' inclusion criteria and analysis of data.