Outdated Frameworks, Missed Opportunities: A Call for Establishing Classification Criteria for Patients with Sarcoidosis.

Progress in sarcoidosis research is hampered by inconsistent definitions and study entry criteria that rely on variable local practice patterns and widely differing expert opinions. This, in turn, has resulted in a heterogeneous body of clinical trial data that often cannot be compared, replicated, or generalized. The rheumatology community has successfully distinguished between diagnostic and classification criteria for diseases such as systemic lupus erythematosus, IgG4-related disease, and systemic sclerosis. This task was also successfully accomplished for patients diagnosed with pulmonary diseases, such as pulmonary arterial hypertension, asthma, and chronic obstructive pulmonary disease, for which classification has established distinct treatment pathways between groups. Diagnostic criteria are used at the bedside, on a patient-by-patient basis. They reflect the needs of health care providers and clinicians to consider disease heterogeneity and exercise judgment. Classification criteria, however, are primarily used for research and aim for specificity to define homogeneous populations for study. Unfortunately, sarcoidosis does not have definite classification criteria. Their absence undermines proper interpretation of study outcomes and hampers development of novel therapies. Sarcoidosis can be thought of as "constellations of patient populations" that need to be unified. As clinician-researchers and, above all else, advocates for our patients, we must move beyond diagnosis of exclusion and define sarcoidosis by what it is rather than by not what it is not.