Mixed connective tissue disease

Mixed Connective Tissue Disease (MCTD): An Overview

A ribbon the Multifaceted Nature of MCTD

Mixed Connective Tissue Disease, commonly abbreviated as MCTD, is a complex autoimmune disorder that presents a unique combination of symptoms resembling those of systemic lupus erythematosus (SLE), scleroderma, and polymyositis. This article provides an in-depth exploration of MCTD, including its clinical features, diagnostic criteria, underlying mechanisms, and treatment approaches.

Overview and Terminology

MCTD, first described in the late 20th century, is a relatively rare autoimmune disease that falls under the category of connective tissue diseases. It is characterized by the presence of elevated blood levels of a specific autoantibody called anti-U1 ribonucleoprotein (RNP). This autoantibody is a hallmark feature of MCTD and plays a significant role in its pathogenesis.

Clinical Features

MCTD presents a wide array of clinical manifestations that can affect various organ systems. The most common symptoms and clinical features of MCTD include:

Joint Pain and Arthritis

Joint pain and arthritis are prominent symptoms in MCTD, often resembling those seen in rheumatoid arthritis. Patients may experience pain, swelling, and stiffness in multiple joints.

Skin Involvement

Skin abnormalities are common in MCTD, with symptoms such as skin tightening, rash, and fingertip changes reminiscent of scleroderma.

Muscle Weakness

Muscle weakness and myositis, similar to what is observed in polymyositis, can occur in MCTD. This can lead to difficulties in mobility and muscle fatigue.

Raynaud's Phenomenon

Raynaud's Phenomenon: A Vascular Symptom in MCTD

Raynaud's phenomenon, characterized by the abnormal narrowing of blood vessels in response to cold or stress, is a common vascular symptom in MCTD.

Lung and Heart Involvement

In some cases, MCTD can affect the lungs and heart, leading to conditions like interstitial lung disease and pericarditis.

Manifestations include:

• Skin: Raynaud’s phenomenon is universal and almost always is present at the beginning of the disease course. The absence puts the diagnosis in question. The capillary alterations are similar to that of scleroderma. Other cutaneous alterations can be observed similar to the types observed in LES and scleroderma.
• Arthritis: Swollen fingers and occasionally diffuse edema are distinctive signs. Arthritis usually is more frequent and severe than that observed in SLE. Approximately 60% present with an obvious arthritis, with deformities similar to those observed in rheumatoid arthritis.  
• Myositis: Myalgias –muscular aches and pains- are common, but in the majority of patients muscular debilitation, electromyographic alterations , and elevations in muscular enzymes, like in pure polymyositis are not observed.
• Cardiac disease: Pericarditis is the most common cardiac manifestation, observed in 10-30% of patients. Myocardial involvement can also be observed, usually secondary to pulmonary hypertension, as well as conduction anomalies.
• Pulmonary involvement: Is observed in 75% of patients. It can present as pleural effusion, pulmonary hypertension, interstitial lung disease, thromboembolic disease, and others.
• Renal disease: The absence of severe renal disease is a marker of MCTD. Membranous nephropathy can be observed in some cases.
• Gastrointestinal disease: The most common change is the alteration of esophageal motility like that observed in scleroderma.
• Central nervous system involvement (CNS): The original description of this disease stressed the absence of changes to the CNS, however, there have been trigeminal neuropathies (cranial nerve V), sensorineural hearing loss, and headaches observed in patients with MCTD.  
• Hematologic anomalies: The presence of mild anemia and hypergammaglobulinemia are common, other hematologic anomalies such as those observed in SLE can also be observed..
• Laboratory value changes: Rheumatoid factor is positive in 50-70% of patients, and anti–citrullinated protein antibody is detected in 50% of patients. The universal serological findings in patients with MCTD is the presence of anti-nuclear antibody, with anti-nRNP specificity, especially antibodies against protein 68 kD.

Genetics

The contribution of genetics toward developing MCTD is unknown. Family members have been known to develop MCTD suggesting that genetics may play a role in MCTD, however most cases present individually. As MCTD can present with comorbid connective tissue diseases there must be a genetic link, however it has not yet been discovered. DNA methylation may affect the as yet unknown genetic risks of this disease as patients with MCTD have decreased DNA methylation levels in opposition to their healthy counterparts.

Pathophysiology

MCTD is an autoimmune disorder. Anti-RNP antibodies develop against RNP when RNP is found outside of the nucleus. RNP is immunologically protected due to its location, however if a cell dies and RNP is no longer contained in the nucleus and thus unprotected, the immune system can respond by forming antibodies due to cellular mimicry. Risk to develop MCTD can increase if the body has exposed to molecules or viruses with a similar structure to RNP in the past.

There are currently no known environmental factors or triggers contributing to MCTD.

It has been associated with HLA-DR4.

Diagnosis

Distinguishing laboratory characteristics are a positive, speckled anti-nuclear antibody and an anti-U1-RNP antibody.

After the original 1972 description of MCTD by Sharp, there was some controversy over whether MCTD was a distinct connective tissue disease, however after four decades and more than 2000 publications, it seems that there is a consensus that MCTD should be considered a distinctive clinical entity, and is thus considered as such by the majority of rheumatologists, however there is a subgroup of patients that could evolve in their disease course towards another connective tissue disease.

Although almost any organ can be affected by MCTD, there are various clinical manifestations that make it more likely to suspect the disease is MCTD over other connective tissue diseases:

1. Raynaud’s phenomenon.
2. Edematous hands and swollen fingers.
3. Arthritis more severe than that of SLE.
4. Pulmonary hypertension (does not need to be pulmonary fibrosis) differentiates MCTD from SLE and scleroderma.
5. Anti-RNP antibodies in elevated levels, especially antibodies against protein 68 kD.
6. Absence of severe renal or CNS disease.

Several criteria have been described to standardize the diagnosis of the disease, some of the most used being those of Alarcón-Segovia, although there are no universally accepted criteria. In general the criteria require the presence of high titres of anti-RNP antibodies, the presence of some characteristic signs of the disease –Raynaud or swollen hands/fingers– and the presence of some clinical manifestations of at least two other connective tissue diseases –SLE, scleroderma, polymyositis.

A. Serologic criteria: Positive Anti-RNP at a titre> 1:1600 by hemagglutination

B. Clinical Criteria 1. Edema of the hands 2. Synovitis 3. Myositis 4. Raynaud’s phenomenon 5. Acrosclerosis

MCTD is present with: Criteria A together with 3 or more clinical criteria –one of which must be synovitis or myositis–

It is often several years before sufficient signs and symptoms appear to make the diagnosis of MCTD, relative to the more sequential clinical manifestations of SLE, scleroderma, and polymyositis, so often, in the initial phases, the diagnosis most appropriate for patients is “undifferentiated connective tissue disease”.

If the patient has edematous hands and/or swollen fingers in conjunction with elevated titers of antinuclear antibodies, an elevated titre of anti-U1 RNP antibody is a good predictor of progressing to MCTD. The presence of this specific antibody is sine qua non for the diagnosis of MCTD, although its isolated presence does not guarantee that a patient has MCTD or will develop it. If the dominant autoantibodies are  antiDNAn, Sm, Scl70 or Ro, it is likely the patient will develop another connective disease distinct from MCTD. The clinical manifestations of MCTD appear correlated more intensely to the antibodies against protein A’ and 68 kD of the U1 RNP complex. The typical phenotype of MCTD also appears to be in part genetically determined, as patients with MCTD are associated with HLA-DR4 or HLA-DR2, meanwhile those with SLE are associated with HLA-DR3 and those with scleroderma are associated with HLA-DR5.

SLE, scleroderma, and in MCTD have antibodies against anti-U1-snRNP at differing percentages. These antibodies are in most MCTD patients but are seen in only 30-35% of SLE and 2-14% of scleroderma patients, therefore they can help differentiate MCTD from other connective tissue disorders.  There are different haplotypes of SNRNP70 which due to their differences in patients with MCTD versus those with SLE or scleroderma help substantiate the claim that MCTD is a separate disease. The T-G-CT-G haplotype is more common in patients with MCTD, whereas the T-G-C-G haplotype is more commonly seen in scleroderma and SLE.  

Treatment

Although MCTD was originally described as a disease with a good treatment response to corticosteroids, the treatment of the disease is based on the specific manifestations and clinical complications, similar to how other signs and symptoms are treated in other connective tissue disease.

Standard

For arthritis, non-steroidal anti-inflammatories or low dose prednisone are usually used, which can be used in association with methotrexate or hydroxychloroquine. Temporomandibular joint arthritis has been shown to be successfully treated with condylar reconstruction using chondral grafts. Higher doses of corticosteroids (0.25 to 1 mg/kg/day) are used in complications such as myositis, meningitis, pleuritis, pericarditis, myocarditis, interstitial lung disease, or hematologic abnormalities. On the contrary, Raynaud’s phenomenon, acrosclerosis or peripheral neuropathies are usually resistant to corticosteroids. Cyclophosphamide are useful in interstitial lung disease and in the eventual serious renal involvement. In cases of myositis or thrombocytopenias resistant to corticosteroids, intravenous immunoglobulins may be useful. For Raynaud, general measures (such as tobacco cessation, protection against the cold), calcium antagonists, endovenous prostaglandins or endothelin-2 antagonists may be useful. In patients with gastroesophageal reflux, proton pump inhibitors and H2 receptor antagonists can be used, following protocol for the usual treatment of these scleroderma problems.

Since pulmonary hypertension is the leading cause of death, its early diagnosis by routine echocardiography and the rapid initiation of treatment with endothelin-1 antagonists (bosentan), phosphodiesterase 5 inhibitors (sildenafil) or endovenous prostacyclins (epoprostenol) manage to considerably improve morbidity and mortality.

Investigational

Further investigation into appropriate treatment options for MCTD are in progress.  Treatment for various rheumatoid diseases are currently undergoing research and have the potential to be used for patients presenting with similar signs and symptoms.  Better understanding the pathophysiology of the disease and its progression will enable better targeted treatment options.

Prognosis

The original description of the disease is characterized by a generally good prognosis and an excellent response to treatment with corticosteroids; however, in actuality it is clear that there is a group of patients with elevated morbidity and mortality. In a recent study the survival rates at 5, 10, and 15 years were 98%, 96%, and 88% respectively, with the main causes of death being pulmonary hypertension, cardiovascular problems, and infections. The presence of anticardiolipin antibodies is a more serious risk factor for the disease, as well as the presence of more scleroderma and polymyositis signs and symptoms.

Morbidity is quite high in patients with MCTD. In addition to fatigue and recurrent musculoskeletal complaints, patients can develop a fibromyalgia symptom as a result of occasional outbreaks requiring medium-high doses of corticosteroid.  The steroids, in combination with their adverse effects, frequently cause fibromyalgia symptoms and thus complicate treatment.

The prognosis of mixed connective tissue disease is in one third of cases worse than that of systemic lupus erythematosus (SLE). In spite of prednisone treatment, this disease is progressive and may in many cases evolve into a progressive systemic sclerosis (PSS), also referred to as diffuse cutaneous systemic scleroderma (dcSSc) which has a poor outcome. In some cases though the disease is mild and may only need aspirin as a treatment and may go into remission where no Anti-U1-RNP antibodies are detected, but that is rare or within 30% of cases.

Most deaths from MCTD are due to heart failure caused by pulmonary arterial hypertension (PAH).

Disease progression

Patients diagnosed with MCTD may progress to a clinical picture more consistent with other connective tissue diseases like SLE, scleroderma, or rheumatoid arthritis. In some studies these patients become reclassified over time with other diseases, such as rheumatoid arthritis in 9%, SLE in 15%, and scleroderma in 21% of cases. Such progression is, in part, determined genetically, thus SLE is more likely in patients with HLA-DR3 and scleroderma in patients with HLA-DR5.

Epidemiology

The prevalence of MCTD is higher than that of dermatomyositis and lower than that of SLE. In a 2011 Norwegian study, the prevalence of MCTD was 3.8 per 100,000 adults, with an incidence of 2.1 per million per year.

MCTD is much more frequent in women than in men at between a 3:1 to 16:1 ratio, and in women younger than 50. The general age at onset is around 15–25 years old.

Diagnostic Criteria

Diagnosing MCTD can be challenging due to its overlap with other connective tissue diseases. However, certain diagnostic criteria have been established, including:

Anti-U1 RNP Antibody

The presence of anti-U1 RNP antibody in the blood is a key diagnostic marker for MCTD. A blood test is used to detect the elevated levels of this autoantibody.

Clinical Criteria

Clinical evaluation, including a combination of symptoms resembling SLE, scleroderma, and polymyositis, is used to support the diagnosis.

Additional Tests

Additional tests such as imaging studies, lung function tests, and skin biopsies may be conducted to assess the extent of organ involvement.

Management and Treatment

Managing MCTD typically involves a multidisciplinary approach that may include rheumatologists, pulmonologists, and other specialists. Treatment strategies often focus on relieving symptoms, reducing inflammation, and preventing complications. Common treatment options include:

Immunosuppressive Medications

Immunosuppressive drugs, such as corticosteroids and disease-modifying antirheumatic drugs (DMARDs), are often prescribed to suppress the immune system's abnormal response.

Physical Therapy

Physical therapy plays a crucial role in managing muscle weakness and improving mobility.

Symptomatic Relief

Various medications and interventions may be used to alleviate specific symptoms, such as pain relievers for joint pain or medications to manage Raynaud's phenomenon.

See Also

• Autoimmune Diseases - Explore other autoimmune disorders with similar underlying mechanisms.
• Systemic Lupus Erythematosus - Learn more about another connective tissue disease related to MCTD.
• Scleroderma - Explore scleroderma, a condition that shares clinical features with MCTD.

• Autoimmunity
• Overlap syndrome
• Rheumatoid arthritis
• Autoimmune disease
• Scleroderma
• Systemic lupus erythematosus
• Polymyositis
• Rheumatology

Rheumatologic diseases

Arthritis is often used to refer to any disorder that affects the joints. Rheumatic diseases usually affect joints, tendons, ligaments, bones, and muscles. Rheumatologic diseases usually affect joints, tendons, ligaments, bones, and muscles.

Connective Tissue Diseases

Rheumatology and	Connective Tissue Diseases
Ankylosing spondylitis	Arthritis
Arthritis and Rheumatic diseases	Autoimmune diseases
Autoinflammatory diseases	Behçet’s disease
Bursitis	Giant cell arteritis
Gout	Juvenile arthritis
Knee problems	Lupus
Osteoarthritis	Polymyalgia rheumatica
Psoriatic arthritis	Reactive arthritis
Rheumatoid arthritis	Scleroderma
Sjögren’s syndrome	Systemic lupus erythematosus (Lupus)
Tendinitis	Rheumatologic diseases

Further reading

• Alana M. Nevares, Mixed Connective Tissue Disease (MCTD), MSD Manual: Consumer edition (April 2018), Professional edition (February 2018)
• Shiel, William C. (May 2016). Driver, Catherine Burt (ed.). "Mixed Connective Tissue Disease (MCTD)". MedicineNet.com. {{cite web}}: Unknown parameter |name-list-format= ignored (help)

• Nevares, Alana M.; Larner, Robert. "Mixed Connective Tissue Disease (MCTD): Autoimmune Rheumatic Disorders". Merck Manual Professional. {{cite web}}: Unknown parameter |name-list-format= ignored (help)

External links

Classification	ICD-10: M35.1 MeSH: D008947 DiseasesDB: 8312
External resources	eMedicine: med/3417 Orphanet: 809

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