What Is Mixed Connective Tissue Disease (MCTD)?

Mixed connective tissue disease (MCTD) is a rare autoimmune condition; it is often referred to as an overlap disease because the symptoms of MCTD overlap with other connective tissue conditions, including polymyositis, scleroderma and systemic lupus erythematosus (SLE). In some cases, MCTD also mimics symptoms of rheumatoid arthritis.

Autoimmune diseases develop when the immune system mistakenly attacks healthy cells; mixed connective tissue disease occurs when the immune system attacks the fibers that support the framework of the body. An estimated 25% of individuals with a connective tissue disease develop another connective tissue condition over the course of several years.

Symptoms

Symptoms of mixed connective tissue disease gradually develop over a number of years. Symptoms vary from person to person and include, but are not limited to, the following:

Common symptoms

• Raynaud’s phenomenon*
• Joint pain and/or swelling, especially in the fingers
• Skin rash or tight patches of skin (especially on the knuckles)
• Fatigue
• Mild fever
• Muscle weakness or pain (similar to that of rheumatoid arthritis)
• Stomach inflammation
• Acid reflux
• Chest pain
• Difficulty breathing
• High blood pressure

*An estimated 90% of people with MCTD also have Raynaud’s phenomenon, which is characterized by cold and numb fingers or toes that may become blue, white or purple due to reduced blood flow from stress or cold. Raynaud’s phenomenon can develop years before other symptoms appear.

Less common symptoms

• Polymyositis (an autoimmune disorder that causes severe muscle weakness, especially in the shoulders and upper arms)
• Aseptic meningitis (inflammation of the brain and spinal cord)
• High fever
• Gangrene of the fingers or toes
• Myelitis (inflammation of the spinal cord)
• High fever
• Abdominal pain
• Hearing loss
• Swelling or edema of the hands
• Loss of hair
• Peripheral neuropathy

Advanced stages of mixed connective tissue disease may affect the lungs, heart or kidneys.

Causes

The exact cause of mixed connective tissue disease is unknown; however, researchers are currently attempting to identify proteins produced by the immune system that may play a role in the development of MCTD.

Risk factors

Although mixed connective tissue disease may occur more often in people who have a family history of the condition, the role of genetics is unclear. Other risk factors include, but are not limited to, the following:

• Exposure to certain viruses may increase the risk of developing MCTD.
• Exposure to chemicals, such as polyvinyl chloride and silica, may cause MCTD.
• MCTD can occur at any age; however, it is diagnosed more frequently in women under the age of 50.