Mixed Connective Tissue Disease (MCTD): Overlap Syndrome Features and Management

MCTD is a distinct overlap syndrome combining features of systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and polymyositis (PM), with high-titer anti-U1-RNP antibodies as serologic hallmark.

Clinical Features

• Raynaud's phenomenon: Nearly universal (90–95%); often earliest sign.
• Arthritis/arthralgia: Non-erosive, symmetric (SLE-like).
• Myositis: Proximal weakness, elevated CK (PM-like).
• Skin: SLE-like malar rash, photosensitivity; SSc-like sclerodactyly, telangiectasia.
• Pulmonary: ILD (NSIP pattern), pulmonary hypertension (major mortality driver).
• Cardiac: Pericarditis, myocarditis, conduction defects.
• Renal: Usually mild (mesangioproliferative); less severe than SLE.
• GI: Esophageal dysmotility (SSc-like).
• Neurologic: Trigeminal neuropathy, cognitive, aseptic meningitis.

Diagnosis

• Alarcón-Segovia / Kasukawa criteria: Clinical features plus high-titer anti-U1-RNP.
• Anti-U1-RNP: High titer, speckled ANA pattern; essential for diagnosis.
• Exclude other CTDs (anti-dsDNA, anti-Sm, anti-Scl-70, anti-centromere, anti-Jo-1).

Treatment (Organ-Based)

• General: Hydroxychloroquine (all patients—reduces flares, thrombosis, lipid benefit).
• Raynaud's: Calcium channel blockers (nifedipine), PDE5 inhibitors, topical nitrates.
• Arthritis: NSAIDs, low-dose prednisone, methotrexate, azathioprine.
• Myositis: Glucocorticoids + steroid-sparing (MTX, azathioprine, mycophenolate, IVIG, rituximab).
• ILD: High-dose steroids + mycophenolate or cyclophosphamide; nintedanib for progressive fibrosis.
• Pulmonary hypertension: PAH-specific therapy (ERAs, PDE5i, prostanoids); early referral.
• Severe organ-threatening: Pulse steroids, cyclophosphamide, rituximab.

Monitoring

• PFTs + echo annually (screen PH/ILD).
• CBC, creatinine, LFTs, CK, urinalysis every 3–6 months on immunosuppression.
• Anti-U1-RNP titers not reliable for disease activity.

Prognosis

• 10-year survival >80%.
• Major causes of death: PH, ILD, infection, cardiac.
• Early aggressive management of PH/ILD improves outcomes.

MCTD requires rheumatology-led multidisciplinary care (pulmonology, cardiology, neurology, dermatology) for optimal organ-specific management.