Mixed connective tissue disease — SCE Rheumatology MCQ

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ModerateConnective Tissue DiseasesMixed connective tissue diseaseSCE Rheumatology

A 28-year-old woman has Raynaud's phenomenon, swollen fingers, inflammatory arthritis and mild proximal weakness. ANA is speckled at high titre and anti-U1 RNP antibody is strongly positive. Anti-dsDNA, anticentromere and anti-Jo-1 are negative. Urinalysis is normal. What is the most likely diagnosis?

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Correct answer: C — Mixed connective tissue disease

Explanation lettering: D = shown as B · B = shown as C · E = shown as D · C = shown as E

Mixed connective tissue disease is best because overlap features with high-titre anti-U1 RNP support mixed connective tissue disease. A is less suitable because antisynthetase syndrome would be supported by anti-Jo-1 or related antibodies and ILD; C is less suitable because early RA does not explain Raynaud's, swollen fingers and myositis features; D is less suitable because diffuse systemic sclerosis would have proximal skin thickening and SSc-specific antibodies; E is less suitable because SLE is less likely without dsDNA/Sm and with dominant swollen-hand overlap phenotype. Clinical pearl: anti-U1 RNP is the key serological clue in MCTD-style stems.

Reference: EULAR/ACR classification criteria; Oxford Textbook of Rheumatology