The concept of overlap syndromes implies the occurrence of two or more well-defined connective tissue diseases in the same patient. OSs are not frequent, and their descriptions in the literature are limited to a few case reports and case series.
Iaccarino, L., Gatto, M., Bettio, S., Caso, F., Rampudda, M., Zen, M., . . . Doria, A. (n.d.). Overlap connective tissue disease syndromes. Autoimmunity Reviews., 12(3), 363-373.
Overlap Syndromes have been defined as entities satisfying classification criteria of at least two connective tissue diseases occurring at the same or at different times in the same patient. Connective tissue diseases include systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis, polymyositis/dermatomyositis, and Sjögren syndrome. Every combination between these disorders has been reported. In some overlap syndromes a specific autoantibody has been identified, supporting the hypothesis that these syndromes are not a mere association of two or more connective tissue diseases in the same patient, but a well-defined clinical entity with specific clinical characteristics