Overlap/undifferentiated syndromes

Undifferentiated connective tissue disease (UCTD) and overlap syndromes both form part of the broad spectrum of connective tissue disease. They are difficult to define, as the boundaries between them and specific diseases such as systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and myositis are often not clear-cut. This chapter gives a broad overview of diagnosis, clinical features, outcomes, and management. Patients with UCTD have clinical and/or serological features of connective tissue disease but do not fulfil the criteria for any one defined disease. Raynaud’s phenomenon and puffy fingers are often the presenting features but there are many possible others, including arthralgia, sicca symptoms, and breathlessness due to pulmonary fibrosis, usually in the context of a positive anti-nuclear antibody (ANA). A proportion of patients evolve into a defined connective tissue disease: in those who do, this is generally within 5 years of onset. Treatment is dependent upon the clinical features: for example vasodilators for Raynaud’s phenomenon, or hydroxychloroquine for arthralgia/arthritis. Patients with overlap syndromes have features of more than one defined connective tissue disease. Overlap syndromes are therefore highly heterogeneous as many combinations of clinical and serological features can occur. Mixed connective tissue disease (MCTD) is the overlap syndrome that has been most described and includes overlapping features of SLE, SSc, and myositis in patients who are anti-U1 ribonucleoprotein (RNP) antibody positive. Treatment is of the specific clinical manifestations. Patients with overlap syndromes should be kept under regular review to allow early identification of internal organ involvement.