Mixed, overlap, and undifferentiated connective tissue diseases in current rheumatology

Hrnčíř Zb. Mixed, overlap, and undifferentiated connective tissue diseases in current rheumatology

The diagnostic classification of systemic connective tissue diseases (CTDs) is descriptive. For classic CTDs internationally authorized classification criteria are generally used, but for CTDs outside of classic CTDs no comparable classification systems are available. This group of CTDs includes the following diseases: (a) Mixed connective tissue disease (MCTD) with the obligatory condition of high seropositivity of anti-U₁RNP antibodies and particular manifestations of classic CTDs, which are the basis for four parallelly used diagnostic classifications, (b) overlap syndromes of classic CTDs and MCTD, and (c) undifferentiated connective tissue disease (UCTD) with long-term persistence of particular clinical symptoms of CTDs, and seropositivity of autoantibodies. A minor part of patients with MCTD/UCTD differentiate into one of the classic CTDs in time, but in the majority of patients, persistence is long-term. Interstitial lung disease represents a serious prognostic risk. Long-term monitoring of patients with MCTD, overlap syndromes and UCTD is a prerequisite of good clinical practice. Education, hydroxychloroquine in standard regimen, and therapy according to actual clinical manifestations is an obligatory triad of measures during regular follow-ups. An overview of current knowledge on these atypical CTDs, which are an integral part of rheumatology practice, is the subject of this article.