What Is Mixed Connective Tissue Disease (MCTD)?

A Disease of Overlapping Symptoms

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Mixed connective tissue disease (MCTD) is an autoimmune disease with overlapping characteristics of three other connective tissue diseases—systemic lupus erythematosus, scleroderma, and polymyositis.

Cause

The cause of MCTD is not known. About 80 percent of people diagnosed with MCTD are women. The disease affects people from 5 to 80 years of age with the highest prevalence among adolescents or people in their 20s.

There may be a genetic component but it's not directly inherited.

Symptoms

Early symptoms of mixed connective tissue disease are much like symptoms associated with other connective tissue diseases and may include:

Less common symptoms associated with MCTD include severe polymyositis (mostly affecting the shoulders and upper arms), acute arthritis pain, aseptic meningitis, myelitis, gangrene of the fingers and toes, high fever, abdominal pain, neuropathy of the trigeminal nerve in the face, difficulty swallowing, shortness of breath, and hearing loss. The lungs are affected in up to 75 percent of people with MCTD. About 25 percent of patients with MCTD have kidney involvement.

Diagnosis

Diagnosing mixed connective tissue disease can be very difficult. Features of the three conditions—systemic lupus erythematosus, scleroderma, and polymyositis—typically do not occur at the same time.

Rather, they usually develop one after the other over time.

There are, however, four factors that would suggest a diagnosis of MCTD rather than an individual connective tissue disorder:

  • High concentrations of anti-U1 RNP (ribonucleoprotein) in the blood
  • The absence of certain issues common with systemic lupus erythematosus, such as kidney problems and central nervous system problems
  • Severe arthritis and pulmonary hypertension (not common in systemic lupus or scleroderma)
  • Raynaud's phenomenon, and swollen hands (not common with systemic lupus)

While the presence of anti-U1 RNP is the primary distinguishing characteristic that lends itself to the diagnosis of MCTD, the presence of the antibody in blood can actually precede symptoms.

Treatment

Treatment of mixed connective tissue disease is geared towards controlling symptoms and managing the severe effects of the disease, such as organ involvement. For example, pulmonary hypertension should be treated with anti-hypertensive medications. Inflammatory symptoms may range from mild to severe, and treatment would accordingly be chosen based on the severity. For less severe inflammation, NSAIDs or low-dose corticosteroids may be given. Moderate to severe inflammation may require higher dose corticosteroids. When there is organ involvement, immunosuppressants may be prescribed.

Outlook

Even with an accurate diagnosis and appropriate treatment, a prognosis can be difficult to formulate. How well a patient does depends on which organs are involved, the severity of inflammation, and the progression of the disease. According to the Cleveland Clinic, 80 percent of people survive at least 10 years after being diagnosed with MCTD.

The prognosis for MCTD tends to be worse for patients with characteristics that are tied to scleroderma or polymyositis.

It is important to note that there can be extended periods which are symptom-free, even with no treatment for MCTD.

Sources:

Bennett R. Anti-U1 RNP Antibodies in Mixed Connective Tissue Disease. UptoDate. http://www.uptodate.com/contents/anti-u1-rnp-antibodies-in-mixed-connective-tissue-disease.

Firestein GS, Kelley WN. Kelleys Textbook of Rheumatology. Philadelphia, PA: Elsevier/Saunders; 2013.

Gunnarsson R, Hetlevik SO, Lilleby V, Molberg Ø. Mixed connective tissue disease. Best Practice & Research Clinical Rheumatology. 2016;30(1):95-111. doi:10.1016/j.berh.2016.03.002.

Mixed Connective Tissue Disease. Cleveland Clinic. https://my.clevelandclinic.org/health/articles/mixed-connective-tissue-disease .

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