Mixed Connective Tissue Disease Diagnosis and Management

Diagnostic Approach

The American Thoracic Society recommends that all patients suspected of having Mixed Connective Tissue Disease (MCTD) must undergo high-resolution computed tomography (HRCT) and pulmonary function tests (PFTs) including spirometry and DLCO at the time of diagnosis, as interstitial lung disease occurs in 40-80% of patients and represents a major cause of mortality 1, 2, 3
Clinical features to assess include Raynaud's phenomenon, sclerodactyly, arthritis, myositis, esophageal dysmotility, and skin manifestations that overlap with systemic sclerosis, SLE, polymyositis, and rheumatoid arthritis 4

The European Respiratory Society identifies high-risk features that predict worse outcomes, including esophageal dilatation and motor dysfunction/dysphagia 5, rheumatoid factor positivity 1, absence of arthritis history 1, high anti-U1RNP antibody titers at baseline 1, and fibrosis on HRCT 3

The American College of Rheumatology recommends mycophenolate as the preferred first-line therapy for MCTD-associated interstitial lung disease, with a target dose of 2g daily 6, 3, 7
Azathioprine is an alternative first-line option 6, 3
Rituximab is an alternative first-line option, particularly if active inflammatory arthritis is present 6, 7
Tocilizumab is an additional first-line option 6, 3

The American Thoracic Society recommends patients with SSc phenotype undergo PFTs every 6 months and annual HRCT for the first 3-4 years after diagnosis 1, 3
All other MCTD patients should undergo annual clinical examination and PFTs, with HRCT only if PFTs show abnormalities 1, 2
Complete blood count should be performed every 2-4 months for immunosuppression monitoring 7
Monitor for FVC and DLCO decline every 3-6 months 7
Nearly 50% of patients experience ILD progression, which is generally slow but continues for several years after diagnosis 1, 3