Mixed connective-tissue disease (MCTD)

Mixed connective-tissue disease is an overlap syndrome — an autoimmune connective-tissue disease that borrows features from several others rather than fitting neatly into one. It combines elements of systemic lupus, systemic sclerosis (scleroderma) and inflammatory muscle disease (myositis), and its defining laboratory feature is a high-titre anti-U1-RNP antibody (with a positive ANA). The typical early picture is Raynaud's phenomenon (fingers turning white and blue in the cold) and puffy, swollen fingers, often with joint pains. Over time, features from the constituent diseases may appear: skin changes and reflux (scleroderma-like), rashes and blood-count changes (lupus-like), and muscle weakness with raised muscle enzymes (myositis-like). The most important organ to watch is the lungs, because interstitial lung disease and raised lung-artery pressure (pulmonary hypertension) can develop and are the main causes of serious harm. It is more common in women. Diagnosis rests on the combination of the overlap features and the high anti-U1-RNP antibody, and it is distinguished from lupus, scleroderma and myositis by that pattern. Treatment targets the active features and, importantly, monitors and manages any lung involvement, under specialist care.

• Anti-U1-RNP antibody — high titre; the defining feature of MCTD.
• ANA — positive, typically in a high titre.
• Creatine kinase — may be raised if there is muscle involvement (myositis overlap).
• Full blood count — for lupus-like changes (low counts).
• Inflammatory markers (ESR, CRP) — may be raised.
• Note — lung function tests and imaging (not blood tests) are central to monitoring for lung involvement.

• Raynaud's phenomenon (fingers turning white/blue in the cold)
• Puffy, swollen fingers or hands
• Joint pains and swelling
• Muscle weakness and pain
• Skin changes and reflux (scleroderma-like features)
• Tiredness
• Breathlessness if the lungs are involved