Distinguishing asthma from sarcoidosis: an approach to a problem that is not always solvable.

BACKGROUND: Because pulmonary sarcoidosis often affects the airway, it is commonly confused with asthma.
METHODS: This article reviews the mechanisms of airflow obstruction in sarcoidosis, the symptoms associated with this phenomenon, and the approach to distinguish sarcoidosis from asthma. DISCUSSION: Because asthma is highly likely in a patient with wheeze, cough, and chest tightness, sarcoidosis is usually not considered unless the patient has extrapulmonary manifestations of sarcoidosis or a family history of the disease. When pulmonary sarcoidosis is a consideration, a chest radiograph should be performed. A chest radiograph should also be performed in an asthmatic patient when the presentation is atypical, or fails to respond to standard asthma treatment; chest radiography should be performed in this situation to consider not only pulmonary sarcoidosis but also other possible cardiopulmonary disorders. In a patient with confirmed pulmonary sarcoidosis, the diagnosis of concomitant asthma is problematic. The symptoms associated with the two disorders are often identical. Airflow obstruction is common in sarcoidosis so that pulmonary function testing is unlikely to differentiate these two diseases. Demonstration of airway hyperreactivity may fail to distinguish these disorders as this is common in sarcoidosis. Serum IgE, serum angiotensin-converting enzyme levels, sputum eosinophilia, and exhaled nitric oxide measurements show promise as distinguishing tests, although they have not been studied specifically. Pulmonary imaging is probably of limited value unless baseline studies are available for comparison. We suspect that historical information will be more useful in distinguishing these two diseases. Not infrequently, it may be impossible to exclude or confirm an asthmatic component in a confirmed pulmonary sarcoidosis patient. Fortunately, exacerbations of both these diseases are often treated with systemic corticosteroids initially. Significant variability in pulmonary symptoms and airflow obstruction suggest that an asthma component is present, and inhaled corticosteroids and bronchodilators should be considered in these cases,
CONCLUSIONS: Asthma and sarcoidosis share many of the same symptoms, as sarcoidosis commonly affects the airways. Therefore, it is problematic to distinguish these two diseases. In this article, we have outlined an approach to assess the presence of each of these diseases and an approach to therapy.