Introduction 

Mixed connective tissue disease, which is also known as MCTD, is a rare autoimmune disease. An autoimmune disease is a condition that happens when your immune system mistakenly attacks the healthy cells in your body.

Mixed connective tissue diseases are defined by the combined features of at least 2 connective tissue diseases occurring concurrently in a person's body, including the following:

• Systemic lupus erythematosus (lupus)
• Systemic sclerosis (scleroderma)
• Polymyositis
• Dermatomyositis
• Rheumatoid arthritis

People who experience mixed connective tissue disease (MTCD) may have symptoms like:

• Cold and numb fingers or toes
• Swollen fingers or hands
• Feeling unwell (Having symptoms like fatigue and mild fever)
• Joint and muscle pain
• Rashes (They can be red or reddish brown and are usually seen in the knuckles)
• Raynaud’s phenomenon 
• Inflammation 

The Role of Imaging in MCTD

Because mixed connective tissue disease is difficult to detect, an accurate diagnosis takes time. In some cases, it takes some months and even years, as the symptoms tend to change and worsen over time. 

However, imaging techniques can be used to diagnose, monitor the progression of the disease and guide the optimal treatment for MCTD.⁴

Imaging Techniques by Organ System

Imaging and other diagnostic tests are only needed to be performed if there is a concern that a particular organ in your body is affected. Some of the tests that can be carried out include:

Cardiopulmonary Testing in MCTD

‘Cardiopulmonary’ describes the integrated system of the heart (cadio-) and lungs (pulmonary-). Therefore, cardiopulmonary tests involve checking how well the heart and lungs are functioning to identify potential problems. The following tests may be used for Cardiopulmonary testing in MCTD:

Chest X-ray

This is a simple imaging test that uses radiation to create an image of your heart, lungs, airways, blood vessels, as well as bones of your spine and chest. It can help to identify:

• Lung problems such as pulmonary infiltrates, interstitial lung disease or pleural effusion.
• Changes in the heart, such as cardiomegaly (having an enlarged heart)

Computed Tomography (CT Scan)

It is a diagnostic imaging procedure or test that combines X-rays with computer algorithms to generate detailed images of the inside of your body. It provides a clearer view of your lungs and shows abnormalities like injuries and diseases. It is also tumour sensitive in lung diseases such as Interstitial lung disease (ILD).

Echocardiogram 

An echocardiogram utilise ultrasound to evaluate the structure and function of your heart. By showing how blood flows through your heart and heart valves, It can be used for screening the following diseases:

• Right heart disease (it is often linked to the lungs as its function is to pump blood to the pulmonary system)
• Pulmonary hypertension (having high blood pressure in the lungs)
• Pericardial effusion (fluid around the heart) or pericardial thickening (when your pericardium becomes abnormally thickened)
• Valve abnormalities and overall heart function

Pulmonary Function Testing (PFT)

It is also known as lung function tests (LFT), which show how well your lungs are working.⁷ It measures how much air enters and leaves your lungs, how much air goes from your lungs to your blood and how well your lungs work during exercise. It can be used to diagnose the following:

• Chronic obstructive pulmonary disease (COPD)
• Pulmonary fibrosis
• Asthma
• Weakness of your breathing muscles
• Narrowing of your trachea 

Right Heart Catheterisation

It is a minimally invasive (low risk) procedure that is used to measure how well the heart is pumping. It is used to confirm pulmonary hypertension in MTCD. A thin flexible tube is inserted into your vein (either vein in your neck, groin or arm) and guided into the right side of your heart to your pulmonary artery to measure blood pressure and oxygen in your heart and lungs. A diagnosis is made if the mean pulmonary arterial pressure is greater than 20mmHg.³

Musculoskeletal Imaging

This technique allows doctors to check your bones, joints and muscles. For example, if you are experiencing pain in your bones, joints or muscles, musculoskeletal imaging can be used to visualise the internal anatomy and assess any abnormalities. Musculoskeletal imaging includes radiographs, computed tomography scans, bone scans, magnetic resonance imaging, and musculoskeletal ultrasonography.⁴ However, these are the three major ones:

• X-ray of the joints: An X-ray of the joints scans your knee, shoulder, hip, wrist, ankle or other joint. It reveals joint damage and shows changes in your joints, such as signs of arthritis
• Musculoskeletal ultrasound: Is an ultrasound imaging that allows doctors to see your muscles, tendons, ligaments, joints, and nerves. It is used for diagnosing muscle strains, nerves and arthritis
• Magnetic resonance imaging (MRI): A test that creates clear images of the structures of the internal areas of your body using radio waves, a large magnet, and a computer. It is often used for disease detection, diagnosis, and treatment monitoring. It requires frequent imaging for treatment monitoring or diagnosis because it doesn’t use radiation like X-ray. One of its advantages is that it detects signs of muscle or joint inflammation on time before it shows obvious symptoms

Additional rests may be required depending on the symptoms:

• To check digestive issues, tests like esophagram, upper endoscopy or colonoscopy may be done for you
• To check for muscle or nerve disease, an electromyogram (EMG) and nerve conduction study may be done. These tests help to know and measure how well your nerves are working

Treatment

How to manage mixed connective tissue disease?

The treatment you receive for MTCD depends mainly on the organs that are affected, the symptoms you feel, and how severe your condition is. In some cases, some people only need medications when the symptoms worsen, while others may need ongoing treatment. The treatment for MTCD is similar to that of lupus, systemic sclerosis, and idiopathic inflammatory myopathy.⁸ There is currently no cure for MTCD, however, it can be managed with the use of the following medications:

• Corticosteroids: They are a class of steroids that can be used to reduce inflammation in your body. In mild cases, your doctor can give you a low dose of this medication to stop your immune system from attacking the healthy cells in your body and to reduce inflammation. However, if it is more severe, you’ll need to take a higher dose
• Antimalarial drugs: Antimalarial drugs such as hydroxychloroquine can be used to treat MCTD in its early stage and help to prevent flare-ups
• Calcium channel blockers: Relax the muscles in your blood vessel walls and help to improve circulation. If you or anyone you know has Raynaud’s syndrome (also known as Raynaud’s phenomenon), calcium channel blockers may be prescribed
• Other immunosuppressants: If the major organs in your body, such as your lungs, the heart or kidneys, are affected by this disease, you'll need a stronger immunosuppressant that will be able to control the immune system and prevent it from having further damage
• Antihypertensive medications: If pulmonary hypertension occurs, you will need to take blood pressure medication to lower your blood pressure. Pulmonary hypertension can lead to heart failure if it's not treated on time. It's the most common cause of death in people with MTCD

FAQ’s

What is the diagnostic test for mixed connective tissue disease?

Going for a blood test can help to detect the specific antibodies that are associated with MTCD. They include antiribonucleoprotein antibodies (it is also called anti-RNP antibodies) and antinuclear antibodies (it is also called ANAs). These antibodies need to be present because they are important for the diagnosis.

What is the difference between lupus and MCTD?

Systemic lupus erythematosus (SLE) is an autoimmune disease and a long-term condition that affects the body and causes joint pain, skin rashes and tiredness, while Mixed connective tissue disease (MTCD) is a rare autoimmune disease that has symptoms of several other diseases, such as lupus, scleroderma, and rheumatoid arthritis.

Can I live a long life with mixed connective tissue disease?

People who experience this disease have an overall survival rate of 96%, but the prognosis varies depending on the severity of the person’s symptoms.⁵

Summary

Mixed connective tissue disease is a rare systemic autoimmune disease. It has the combined features of at least 2 autoimmune diseases. Examples include lupus, rheumatoid arthritis, scleroderma, and other connective tissue diseases. Some of its symptoms include feeling unwell, having cold and numb fingers and toes, Raynaud's phenomenon, joint and muscle pain, e.t.c. As it doesn’t have unique clinical features, it can be misdiagnosed. It affects the skin, muscles, the heart, lungs and the intestine. 

Because of how MCTD can affect the organs of your body, imaging techniques serve as a smart move for detecting, diagnosing, and monitoring this condition. Using only one imaging technique may not be sufficient because of the number of affected organs. Therefore, using two or more imaging techniques may be recommended. The selection of imaging technique depends on the affected organs.   

Cardiopulmonary imaging techniques, such as chest X-rays, help to detect heart and lung complications, such as interstitial lung disease and cardiomegaly. Although right heart catheterization is minimally invasive, it remains the best standard for confirming pulmonary hypertension. 

X-rays, musculoskeletal ultrasounds, and MRI scans are musculoskeletal imaging techniques, used to generate the images of your bones, joints and muscles. One of the advantages of MRI is that it detects inflammation even before obvious symptoms appear in your body.

Tests such as esophagrams and colonoscopy may be used to determine if your nerves are functioning properly. 

Currently, there is no cure for MTCD and it can only be managed to prevent further damage. Applying imaging techniques and using medication is an excellent approach for treating mixed connective tissue disease.