Difference Between UCTD and MCTD - An Overview

Introduction:

Autoimmune diseases are considered to be complex and rare. Signs, symptoms, and autoantibodies determine the specific connective tissue diseases. It was noticed that autoimmune diseases share similar signs and symptoms, making it difficult to identify the exact condition. The differences should be known to determine the condition of autoimmune disease.

What Is Undifferentiated Connective Tissue Disease (UCTD)?

Connective tissue connects, supports, binds, or separates other tissues or organs throughout the body. It involves many, many proteins like collagen and elastin. This condition occurs when there is an impact on the function or structure of connective tissue. There are different types of connective tissue diseases (CTD). There are certain criteria to identify or diagnose them. When a condition does not fit any criteria described, such CTD is called UCTD.

UCTD is described as a serological and clinical manifestation of systemic autoimmune disease. This condition does not fulfill any of the criteria that describe connective tissue diseases like systemic lupus erythematosus, Sjogren’s syndrome, systemic sclerosis, polymyositis, dermatomyositis, or rheumatoid arthritis.

In 1980, LeRoy et al described the early phase of rheumatic disease as UCTD as its features did not meet the criteria of connective tissue disease. It was observed that UCTD is most common among females aged between 32 to 44 years. Most of the cases are found not to progress into full-blown connective tissue disease. It exhibits a sole antibody profile. A study found that UCTD is more common among the white race.

What Are the Causes of UCTD?

Autoimmune diseases do not have exact causes.

1. Genetics and Environmental Factors: The combination of genetics and environmental factors causes most autoimmune diseases. In autoimmune diseases, the spontaneous and exaggerated activity of the immune system can be noted. This type of immune system forms autoantibodies or activates antigenic-specific T cells. These tend to target autoantigens in different organs. Autoimmune connective tissue diseases happen when the immune system affects connective tissues. These may occur due to triggers like environmental factors such as chemicals in cigarette smoke, pollutants in the air, and ultraviolet light.

2. T regulatory Cells: T regulatory cells are thought to be responsible for starting autoimmune connective tissue diseases. Whenever there is a decrease in T-regulatory cells, the disease may manifest. It was also observed that a further reduction in these cells may worsen the condition by differentiating UCTD. This may result in differentiated connective tissue having a poor prognosis.

3. Phases of UCTD:

Like any other autoimmune disease, UCTD occurs in different phases.

• Initial Phase: The initial phase may begin years before the diagnosis. This is because of a lack of signs and symptoms and serological biomarkers.

• Mid Phase: In the subsequent phase, autoantibodies may be detected in the serum though clinical manifestations are absent.

• Final Phase: In the final phase, significant signs and symptoms may appear which lead to a definitive diagnosis. Anti-Ro/SSA and anti-U1-RNP are found to be the most frequently found markers in this disease.

What Are the Symptoms of UCTD?

• Arthralgia (joint pain).

• Arthritis (joints are painful, swollen, and warm).

• Raynaud’s phenomenon is a condition in which extreme color changes are observed in hands and feet in response to cold.

• Dryness of eyes and mouth may be observed.

• Photosensitivity means developing rashes on the skin after exposure to the sun.

• Pleuritis (the lining of the lungs gets inflamed) or pericarditis (inflammation of the lining of the heart) may be observed.

• Rashes on the face worsen after exposure to the sun.

• Oral ulcers can be observed.

Major individuals with UCTD do not manifest major organ damage or life-threatening diseases. This condition is not considered to be a serious condition.

What Is Mixed Connective Tissue Disease (MCTD)?

MCTD is considered to be a rare autoimmune disorder. It was first described in 1972 and is considered a mixed or overlap of three connective tissue diseases. The three connective tissue diseases include:

• Systemic Lupus Erythematosus (SLE): It is an inflammatory disorder affecting many organs of the body. Symptoms of this condition include fever, weakness, joint aches, and skin rashes on the face, neck, and upper body.

• Scleroderma: Abnormal thickening and hardening of the skin may be observed in the underlying tissues and organs.

• Polymyositis: This condition is characterized by inflammation of muscles (swelling).

Individuals affected with MCTD exhibit features of each of these three diseases.

• These individuals typically have increased quantities of antinuclear antibodies (ANA), and antibodies to ribonucleoprotein (anti-RNP) in the blood.

• The symptoms among many individuals with this condition start to evolve eventually and become dominated by features of one of the three illnesses. Most commonly exhibit the scleroderma features.

About 25 percent of individuals with connective tissue disease may develop another connective tissue disorder over time. This is called overlap syndrome. It was noticed that MCTD tends to affect females in their 20-30 years of age. Even children may be affected by this condition. MCTD was found to affect all races.

To arrive at the specific diagnosis of MCTD, may require many years. Hence, in the initial stage, MCTD exhibits features of UCTD.

What Are the Causes of MCTD?

The cause of MCTD is not known. It was observed that it is not an inherited condition, though some researchers have found that it may be related to family history. It was known that some viruses and chemicals like polyvinyl chloride and silica are other possible causes.

What Are the Symptoms of MCTD?

The symptoms of MCTD appear to be similar to other connective tissue disorders. These include:

• Weakness.

• Pain is experienced in muscles without any cause.

• Joint pains are felt.

• Low-grade fever.

• Raynaud's phenomenon (decreased blood flow to the fingers, toes, ears, and nose).

Less common early symptoms include:

• Severe polymyositis that occurs in the shoulders and upper arms.

• Intense arthritis.

• Aseptic meningitis may occur (brain and spinal cord inflammation not caused by bacteria or viruses).

• Myelitis (inflammation of the spinal cord) may occur.

• Gangrene of toes and fingers may occur.

• Abdominal pain, high fever, and hearing loss.

• Neuropathy (affecting trigeminal nerve in the face) may be noticed.

Classic symptoms include:

• Raynaud’s phenomenon.

• Swollen and sausage-like fingers may occur.

• Joints and muscles get inflamed.

• Pulmonary hypertension (high blood pressure in the lungs' blood vessels) may occur.

Conclusion:

UCTD and MCTD are connective tissue disorders that exhibit different characteristics. UCTD is different from MCTD in certain features. There are very narrow differences that help differentiate UCTD and MCTD. Hence it becomes important to know in detail about UCTD and MCTD. Knowing about these conditions helps in the early diagnosis. This helps in effective treatment. Effective treatment helps achieve a good quality of life.