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Undifferentiated systemic rheumatic (connective tissue) diseases and overlap syndromes

Richard S Panush, MD, MACP, MACR
Neil Kramer, MD, FACR, FACP
Elliot D Rosenstein, MD, FACR, FACP
Section Editor
Robert H Shmerling, MD
Deputy Editor
Monica Ramirez Curtis, MD, MPH


As much as 25 percent of rheumatic disease patients with systemic symptoms cannot be definitively diagnosed. Furthermore, the majority of these patients will remain undiagnosed during 5 to 10 years of follow-up [1-3].

Such patients were historically described as having "collagen" or "connective tissue" diseases, since they shared similar clinical and pathologic features of widespread inflammation [3-6]. Subsequently, these patients have been considered to have "diffuse" or "undifferentiated" (or sometimes "early undifferentiated") "connective tissue diseases" (UCTD) [3,7-12]. Other patients with rheumatic diseases have systemic features that overlap two or more specific, recognized entities and also cannot be definitively diagnosed [2,3,13-15].

Increasingly, the term "systemic rheumatic" disease has replaced "collagen," "collagen-vascular," or "connective tissue" disease. This change reflects the recognition that these disorders probably represent perturbations of the immune system with resultant inflammatory tissue injury rather than primary disorders of collagen, vasculature, or connective tissue; the inciting events are not yet clear.

This topic review provides an overview of undifferentiated systemic rheumatic diseases and overlap disorders, together with an overall approach to the patient.


The American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) have developed classification criteria to assist in the categorization and diagnosis of patients with rheumatic diseases. These classification criteria do not substitute for identification of unique, defining etiologic, clinical, or immunopathologic features for systemic rheumatic diseases, which remain unknown for most of these disorders.

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Literature review current through: Oct 2017. | This topic last updated: Oct 05, 2017.
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