There are two types of connective tissue diseases: mixed connective tissue disease (MCTD) and undifferentiated connective tissue disease (UCTD). The symptoms and signs of mixed connective tissue disease sometimes overlaps with the other autoimmune diseases and it’s difficult to diagnose if it is mixed connective tissue disease or if it’s an autoimmune disease. The clinical features seen are a combination of systemic lupus erythematosus (SLE), scleroderma, rheumatoid arthritis and polymyositis clinical features.
Therefore, mixed connective tissue disease is also known as overlap syndrome.
There are many antibody tests done when mixed connective tissue disease is suspected. These tests are done to diagnose or rule out other autoimmune diseases.
Sometimes patients with mixed connective tissue disease will have those antibodies tests positive and there is only one antibody test specific to mixed connective tissue disease, but that also can be positive falsely in some instances. It is really difficult to diagnose mixed connective tissue disease; the diagnosis is based on the history, physical examination and investigation findings.
What Antibody Is Associated With Mixed Connective Tissue Disease?
The exact etiology of mixed connective tissue disease is unknown, it may be due to B lymphocytes hyperactivation, T lymphocytes increased activity causing the autoimmune reactions.
There are several antibody tests done for mixed connective tissue disease since, it shows clinical features of auto immune diseases therefore, the antibody tests become positive and may be these antibodies are associated with the pathogenesis of mixed connective tissue disease.
Antinuclear Antibodies (ANA). Positive in patients with systemic lupus erythematosus patients (SLE), this test is very sensitive in detecting SLE but less specific. If ANA is negative it’s unlikely that person has SLE, but it can be positive in other diseases such as liver diseases, virus infections, due to drugs and even in healthy people. ANA is positive almost in all SLE patients.
Anti-Double-Strand DNA Antibodies (anti-ds DNA). More specific in diagnosing SLE. If both ANA and anti-dsDNA antibodies are positive the diagnosis of SLE can be confirmed. 43-92% of cases with mixed connective tissue disease had anti-dsDNA positive, the specificity was about 89-99% and sensitiveness was about 8-54%.
Anti–Ribonucleoprotein (RNP) Antibodies. Anti-RNP bodies are needed for the diagnosis of mixed connective tissue disease and usually titers are typically high. Anti-RNP is found in 95-100% of mixed connective tissue disease cases. Anti–U1-RNP is characteristic of mixed connective tissue disease. Anti-RNP antibodies are helpful in the disease monitoring as well because, these become undetectable when the disease goes into a remission stage. These antibodies are frequently associated with nuclear coarse speckled pattern on Hep2 cells.
Scleroderma-Specific Antibodies. There are lots of antibodies associated with scleroderma also known as systemic sclerosis. Anti-centromere, anti–Scl-70 (topoisomerase), Anti-RNA polymerase III, Anti-U1-RNP, Anti-Ku and anti–PM-1 (Pm-Scl). Anti-centromere, anti–Scl-70 (topoisomerase) and anti–PM-1 (Pm-Scl) can be positive in mixed connective tissue disease.
Anti-Ro/SSA And La/SSB Antibodies. Commonly positive in primary Sjogren’s syndrome, it’s positive in 60-70% of cases. It can be positive in SLE, mixed connective tissue disease and scleroderma sometimes. Anti-Ro/SSA immunoglobulin G (IgG) antibodies are very common in UCTD.
Antiphospholipid Antibodies. Anticardiolipin antibodies and lupus anticoagulant can be positive when pulmonary hypertension is present.
Myositis Associated Antibodies. There are many types of different myositis associated antibodies and these also can be positive with mixed connective tissue disease.
High-Titer Speckled Pattern Fluorescent Antinuclear Antibody (FANA). Seen typically in mixed connective tissue disease, however this is not specific for mixed connective tissue disease.
Rheumatoid Factor. This can be positive in many of the patients with mixed connective tissue disease and it can be positive in patients with rheumatoid arthritis (50-70%).
Conclusion
The symptoms and signs of mixed connective tissue disease (MCTD) sometimes overlaps with the other autoimmune diseases and it is difficult to diagnose if it is mixed connective tissue disease or if it is an autoimmune disease. The clinical features seen are a combination of systemic lupus erythematosus (SLE), scleroderma, rheumatoid arthritis and polymyositis clinical features. Therefore, mixed connective tissue disease is also known as overlap syndrome. There are several antibody tests done for mixed connective tissue disease since, it shows clinical features of auto immune diseases therefore, the antibody tests become positive and may be these antibodies are associated with the pathogenesis of mixed connective tissue disease. Antibodies associated are. Antinuclear antibodies, Anti- double-strand DNA antibodies, Anti–ribonucleoprotein (RNP) antibodies, Scleroderma-specific antibodies like Anti-centromere, anti–Scl-70 (topoisomerase) and anti–PM-1 (Pm-Scl); Anti-Ro/SSA and La/SSB antibodies, Antiphospholipid antibodies, Myositis associated antibodies, High-titer speckled pattern fluorescent antinuclear antibody (FANA), and Rheumatoid factor.
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- What Is The Life Expectancy Of Someone With Mixed Connective Tissue Disease?
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