Distinguishing Blau Syndrome from Systemic Sarcoidosis.

Blau syndrome and Sarcoidosis share the characteristic histologic finding of noncaseating granulomas as well as some similar clinical characteristics; nevertheless, they are distinct entities with important differences between them. Blau syndrome and Early Onset Sarcoidosis are due to one of numerous possible gain-of-function mutations in NOD2, commonly presenting before age 5 with a triad of skin rash, arthritis, and uveitis. However, as more cases are reported, expanded clinical manifestations have been described. In systemic Sarcoidosis, there are numerous susceptibility genes that have been identified, and disease is thought to result from an environmental exposure in a genetically susceptible host. It most often presents with constitutional symptoms and pulmonary involvement and typically affects adolescents and adults. This paper reviews the similarities and differences between Blau syndrome and Sarcoidosis. We also discuss the importance of distinguishing between them, particularly with regard to prognosis and outcomes.