Most of the clinical features of MCTD during the initial stages are very non-specific and hence difficult to confirm. Presence of Raynaud’s phenomenon and high levels of serum ANA are useful predictors during this period. The distinctive, overlapping features of the other three connective tissue disorders including SLE, scleroderma and myositis may appear only after a period of disease progression.
The most common sets of clinical manifestations include Raynaud phenomenon and swollen hands/digits, severe form of arthritis and pulmonary hypertension, and high serum titres of anti-U1SnRNPs . Many organs including skin, joints, muscles, heart, lungs, gastrointestinal tract, kidneys, central nervous system, and vascular system are involved in MCTD during various stages of the disease progression. Skin manifestations include Raynaud’s phenomenon, sclerodactyly, swollen digits and calcinosis curtis. Joint involvement is also severe and common in MCTD. Most of the patients develop rheumatoid arthritis, often with in deformities as in boutonniere deformities and swan neck changes. Muscle involvement is in the form of inflammatory myopathy that resemble polymyositis, both clinically and histologically.
Abnormal electrocardiogram is also observed frequently. Right ventricular hypertrophy, right atrial enlargement and abnormality in conduction of signals are commonly reported. About 75% of the patients have pulmonary involvement with a wide variety of problems including pulmonary hypertension, pleural effusions, obstructive airways disease, and pleuritic pain. Also seen are gastrointestinal disorders of different kinds as an overlapping symptom of scleroderma. Low-grade anemia is noted in majority of patients.
Laboratory tests show high serum levels of anti-U1RNP antibodies. Elevated levels of ANA can be observed as speckled pattern in fluorescent antinuclear antibody test. Patients with pulmonary hypertension show antiphospholipid antibodies. More than 60% of the patients are positive to rheumatoid factor. Other immunodiagnostic tests including anti-U1RNA and antibodies against snRNP polyeptides 68kd may also be useful.
Cardiomegaly, effusion, pulmonary hypertension and valvular diseases can be assessed using chest X-ray and echocardiography. CT scan or ultrasonography reveal the presence of visceral perforations, pancreatitis or serositis. Reduced diffusion capacity of lung for carbon monoxide (DLCO) in a pulmonary function test indicate the presence of pulmonary hypertension. Cardiac problems including myocardial ischemia and myocarditis is assessed using ECG. Presence of neuropsychiatric symptoms is monitored through cerebrospinal fluid analysis.
Treatment of MCTD is often based on the organ involved and the progression of the disease. Priority is given to control the symptoms and prevent the development of complications associated with the disorder. Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used to control the symptoms in case of mild MCTD. For those patients who present refractory synovitis, low doses of corticosteroids are recommended. NSAIDs along with hydroxychloroquine is used for symptomatic relief of arthritis. Corticosteroids are suggested in severe forms of MCTD, with the dose depending on the severity and the organ involved.
Calcium channel blockers have vasodilatory effect which is useful in controlling Raynaud’s phenomenon. Phosphodiesterase inhibitors may also be used in Raynaud’s disease and is also helpful in controlling pulmonary hypertension. Pulmonary hypertension, if present, should be the focus of any treatment, as it increases morbidity and mortality. Endothelin receptor antagonists are found to be useful in improving pulmonary hypertension , but has the risk of liver toxicity. Steroid pulse therapy can prevent complications like vascular lesions in patients with pulmonary hypertension . Prostaglandins are also considered to be useful in the management of pulmonary hypertension and the dosage and administration should be done by experts. Immunosuppression using cytotoxic agents along with corticosteroids is suggested in case of organ involvement.
Prognosis is variable in MCTD. Most of the clinical features associated with MCTD develop over a period of time while some like esophageal hypomotility and Raynaud’s phenomenon reduce. In some of the patients the symptoms may enter long-term remission, but in some others it will show severe progression.
A study conducted on a cohort of patients with MCTD showed that features like pulmonary hypertension and pulmonary dysfunction tend to persist even after a period of treatment . This study also reported that most of the patients had a favorable outcome. The most common cause of mortality associated with this disorder is pulmonary hypertension. Morbidity is caused by arthritis, fatigue and dyspnea associated with exertion.
Pathogenesis of this autoimmune disorder is not fully known yet. One of the most characteristic feature of the disease is the presence of high titre of antibodies to U1RNPs. Induction of these antibodies along with alterations of self-antigens and antigenic changes during cell apoptosis are hypothesized to trigger an immune process that result in abnormal activation and responses of B- and T-lymphocytes which in turn lead to clinical manifestations of the disorder .
Some of the hypothesized mechanisms that lead to U1SnRNP induction include spreading of epitopes, modifications during cell apoptosis and activation of toll-like receptor (TLR) .
Prevalence of this disorder remains unknown in different parts of the world. In Japan, MCTD is estimated to affect one in 37,000 people. A multicenter survey conducted in Norway showed a prevalence of 3.8 per 100,000 adults . Females were found to be more affected than males and incidence of MCTD was lower when compared to other connective tissue disorders including SLE, polymyositis and systemic sclerosis.
One of the distinctive features of this disease is the presence of increased levels of U1RNP and U1-70 kd antibodies. Levels of human leucocyte antigens HLA-DR4 and HLA-DRw53 were found to be more in patients with this connective tissue disorder .
MCTD patients have an increased frequency of the allele MICA 129 when compared to patients with other forms of connective tissue diseases . Majority of the patients with MCTD also showed the presence of increased levels of anti-endothelial cell antibodies (AECA) and these were associated with disease activity and vasculitic manifestations . Elevated levels of AECA correlate with increased levels of plasma immunoreactive endothelin-1 .
There is no guideline for the prevention of MCTD.
Mixed connective tissue disease or MCTD is an autoimmune disorder, first identified in patients presenting features of three different connective tissue diseases – systemic lupus erythematosus (SLE), scleroderma and myositis . The differentiating feature of MCTD is the presence of high amounts of antinuclear antibodies (ANAs) and antibodies against U1 small nuclear ribonucleoprotein (SnRNP).
MCTD was considered as a separate disease entity after years of controversies but is now fully characterized as having increased frequency of features including Raynaud’s syndrome, sclerodactyly, myositis, esophageal dysmotility, arthritis, and polymyositis  . As the disease progresses, a subgroup of patients may evolve into having other connective tissue disorders.
MCTD is a rare form of autoimmune disorder characterized by the presence of ‘overlapping’ symptoms of three different connective tissue diseases including SLE (or lupus as it is commonly known as), scleroderma and myositis. As the disease progresses, the symptoms may gradually evolve and become dominated by one of the above-mentioned diseases. The actual cause of the disease is not yet known. MCTD may occur at any age but is more common among women under 30 years of age.
Patients with this disease have high serum levels of anti-U1snRNP antibodies that trigger an abnormal immune response in which the immune system attacks the body’s own tissues. Symptoms of MCTD are varied and may differ from person to person. During the early stages of the disease, non-specific symptoms like fever and fatigue exist. Raynaud’s phenomenon is a common feature of this disease in which the fingers may become cold and numb during stress or in cold conditions. Constriction of blood vessels may cause the fingers to turn pale and then purple. Swelling in the fingers or hands is yet another symptom of MCTD. Swelling and pain in the joints, typical of arthritis, are also common. Some patients may have joint deformities as in the case of rheumatoid arthritis. MCTD may lead to complications including pulmonary hypertension, in which the high blood pressure may affect the blood vessels of the lungs. MCTD may affect many organs. It may also lead to kidney problems and cardiac abnormalities. Some people may develop gangrene, acute arthritis, meningitis, neuropathy, high fever or abdominal pain depending on the organ affected.
Clinical examination and laboratory tests are used to diagnose MCTD. Presence of ‘overlapping’ symptoms along with high serum levels of ANA and anti-U1RNP antibodies are the most important indicators of MCTD. These antibodies are different from the ones present in SLE or scleroderma and thus help in distinguishing MCTD from other common connective tissue disorders.
Treatment of MCTD depends on the symptoms and the type and severity of organ affected. People with mild MCTD may be prescribed NSAIDs for symptomatic relief. Antihypertensive medications are recommended for those who have pulmonary hypertension. Treatment of pulmonary hypertension is very important as it is most important cause of death associated with MCTD. In moderate to severe form of the disease, corticosteroids and immunosuppressants are recommended. For controlling arthritic inflammation, low doses of corticosteroids are used. Patients should regularly monitor their heart condition to prevent cardiac problems. The outcome of MCTD is favorable in most of the cases and timely treatment of the different conditions will help in reducing morbidity associated with connective tissue disorders.