Mixed Connective Tissue Disease (MCTD)

What MCTD is

In autoimmune diseases, the immune system attacks the body's own tissues. In MCTD, the immune system makes antibodies against a protein complex in cell nuclei called U1 small nuclear ribonucleoprotein (U1 RNP). People have a mix of features from three diseases:

• Lupus: rashes, joint pain, mouth ulcers, low blood counts, pleurisy
• Scleroderma: Raynaud's, swollen and tight finger skin, esophageal problems, lung scarring
• Polymyositis: muscle inflammation and weakness

Features of rheumatoid arthritis and Sjögren's syndrome can also occur. MCTD is one of the connective tissue disorders. Some experts consider it a distinct disease, while others see it as an overlap syndrome. Over years, some people's disease evolves to look more like lupus or scleroderma alone.

Symptoms

Early symptoms

• Raynaud's phenomenon: present in nearly everyone with MCTD and often the first sign, sometimes years before anything else. Fingers turn white, then blue, then red with cold or stress.
• Puffy, swollen hands and "sausage-like" fingers.
• Joint pain and swelling, usually in the hands, wrists and knees.
• Muscle aches, and sometimes true muscle weakness.
• Fatigue, low-grade fever and feeling generally unwell.

Later or organ-related symptoms

• Esophagus: heartburn and food sticking, from weak esophageal muscle. This is very common.
• Lungs: breathlessness and dry cough from interstitial lung disease, or pleurisy.
• Pulmonary arterial hypertension: high blood pressure in the lung arteries, causing breathlessness on exertion, fatigue, chest pain, fainting and ankle swelling.
• Skin: tightening of finger skin, rashes, hair thinning and finger ulcers.
• Heart: inflammation of the lining around the heart (pericarditis).
• Nerves: trigeminal neuralgia (sharp facial pain) and, less often, aseptic meningitis.
• Blood: low red cells, white cells or platelets.
• Kidney problems are less common than in lupus.

Causes and risk factors

The cause is unknown. As with other autoimmune diseases, a combination of genes (certain HLA types) and environmental triggers is thought to be involved. About 80% or more of patients are women. It is not contagious and is not usually passed directly from parent to child.

How MCTD is diagnosed

There is no single definitive test, and several sets of diagnostic criteria exist. Diagnosis rests on:

1. Symptoms and exam: especially Raynaud's, swollen hands, arthritis and muscle findings.
2. Antinuclear antibody (ANA): strongly positive, usually with a speckled pattern.
3. Anti-U1 RNP antibodies: high levels are required for the diagnosis. Antibodies typical of lupus (anti-dsDNA, anti-Sm) and scleroderma (anti-Scl-70, anticentromere) are usually absent.
4. Muscle tests: creatine kinase (CK) blood test, and sometimes EMG, MRI or muscle biopsy.
5. Organ screening: pulmonary function tests, a high-resolution chest CT, an echocardiogram to estimate lung artery pressure, and sometimes a right heart catheterization.
6. Other tests: blood count, kidney function, urine tests and nailfold capillaroscopy (a magnified look at the small vessels at the nail base).

MCTD vs lupus and scleroderma

Treatment

Treatment depends on which features are active. A rheumatologist leads care, often with lung, heart and skin specialists.

• Joint pain and fatigue: NSAIDs if safe for you, and hydroxychloroquine, which is commonly used long-term.
• Inflammation flares, myositis and serositis: corticosteroids such as prednisone, ideally at the lowest effective dose for the shortest time.
• Steroid-sparing drugs: methotrexate, azathioprine or mycophenolate.
• Lung scarring: mycophenolate, and cyclophosphamide or rituximab for severe disease.
• Pulmonary arterial hypertension: specialist drugs that widen the lung arteries, along with immunosuppression in some people.
• Raynaud's: keeping warm, stopping smoking and avoiding decongestants, plus calcium channel blockers such as nifedipine if needed.
• Heartburn and swallowing problems: acid-suppressing medicines and lifestyle measures.

Living with MCTD

• Keep warm and protect your hands from cold and injury.
• Do not smoke, because smoking worsens Raynaud's and lung disease.
• Stay active with regular exercise to maintain muscle strength and joint movement.
• Keep up with vaccines. Ask before live vaccines if you take immunosuppressants.
• Plan pregnancies with your rheumatologist, because some medicines must be stopped beforehand and pregnancy needs closer monitoring.

Outlook

The course varies. Many people have mild disease that responds well to treatment, sometimes with long periods of remission. Others develop lung involvement. Pulmonary hypertension is the leading cause of death in MCTD, which is why yearly screening with an echocardiogram and lung function tests is recommended even without symptoms. With modern treatment and monitoring, most people live for many years with the condition.

Frequently asked questions

What are the first signs of mixed connective tissue disease?

The first sign is usually Raynaud's phenomenon, with fingers turning white or blue in the cold. Puffy, swollen hands, joint pain, muscle aches, fatigue and low-grade fevers commonly follow. These early symptoms can come on gradually over months to years.

What is the life expectancy with MCTD?

Most people with MCTD live for many years, and many have a near-normal life span, especially with mild disease. Outlook depends mainly on lung and heart involvement. Pulmonary hypertension is the most serious complication, so regular screening and early treatment are important.

Is MCTD the same as lupus?

No. MCTD shares some features with lupus, such as joint pain and rashes, but also includes features of scleroderma and myositis. It is defined by high anti-U1 RNP antibodies, while serious kidney disease, common in lupus, is less common in MCTD. Over time some people's MCTD evolves into lupus.

What does a positive anti-U1 RNP test mean?

Anti-U1 RNP antibodies are found at high levels in almost everyone with MCTD and are required for the diagnosis. They also occur in some people with lupus and other autoimmune diseases. A positive result is interpreted together with symptoms and other tests by a rheumatologist.

Can mixed connective tissue disease go into remission?

Yes. Some people have long periods with few or no symptoms, especially with treatment. Others have flares, and the disease can change over time to resemble lupus or scleroderma more closely. Regular follow-up helps adjust treatment as the disease changes.