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Mixed Connective Tissue Disease — SCE Rheumatology MCQ

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HardAutoimmune SerologyMixed Connective Tissue DiseaseSCE Rheumatology

A laboratory reports the following autoantibody profile: ANA positive 1:1280 speckled pattern anti-U1 RNP strongly positive anti-Sm negative anti-dsDNA negative. Which condition is most strongly associated with this pattern?

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Correct answer: E — Mixed connective tissue disease with high-titre U1-RNP antibody

The best answer is “Mixed connective tissue disease with high-titre U1-RNP antibody”. High-titre anti-U1 RNP antibody with a speckled ANA pattern and absent anti-Sm and anti-dsDNA is the hallmark serological profile of mixed connective tissue disease (MCTD). While anti-U1 RNP can be seen in SLE, it is typically accompanied by other SLE-specific antibodies. Anti-Sm is specific for SLE. The isolated high-titre anti-U1 RNP without other autoantibodies in the context of overlap features points to MCTD. The competing options represent related diagnoses, tests or treatments, but they do not match the decisive phenotype, safety constraint or management point in this stem.

Reference: Mixed connective tissue disease criteria study: https://pubmed.ncbi.nlm.nih.gov/3798041/