The overlap of Sjögren's syndrome with other systemic autoimmune diseases.

OBJECTIVE: To analyze the main diagnostic problems caused by the overlap between Sjögren's syndrome (SS) and other systemic autoimmune diseases (SAD).
METHODS: We performed a MEDLINE search for articles published between January 1966 and December 2005 that specifically analyzed the overlap between SS and other SAD. We identified a list of diagnostic problems in patients with primary SS who had features considered typical of other SAD.
RESULTS: Clinically, the main diagnostic problems occur in SS patients presenting with arthritis, Raynaud phenomenon, cutaneous features (subacute cutaneous lupus erythematosus, purpura, livedo reticularis, erythema nodosum), interstitial pulmonary disease, and cytopenias (leukopenia, thrombocytopenia). Immunologically, antiphospholipid antibodies (aPL) and antineutrophil cytoplasmic antibodies (ANCA) are the most frequent atypical autoantibodies found in primary SS, with a prevalence ranging between 10 and 20%. However, coexisting antiphospholipid syndrome or systemic vasculitis is only detected in around 10% of SS patients with aPL or ANCA. Anti-DNA and anticentromere antibodies have a prevalence of 5 to 10%, but are more closely related to clinical and/or laboratory data suggestive of associated systemic lupus erythematosus and limited systemic sclerosis, respectively, leading to the fulfillment of classification criteria for these diseases in more than 25% of cases.
CONCLUSION: The wide variety of clinical and immunological manifestations of patients with primary SS often overlap with other SAD, making the differentiation between primary SS, SS associated with SAD, and SS-like presentations of some other SAD difficult. This overlap suggests that the current classification criteria are useful in differentiating between autoimmune and non-autoimmune processes but fail to clearly differentiate among SAD.