Mixed Connective Tissue Disease - MCTD

Mixed connective tissue disease (MCTD) is a complex, systemic, autoimmune disease and generally is described as an overlap syndrome.  Clinically, patients exhibit varied combinations of features common to other systemic autoimmune rheumatic diseases (SARDs) such as systemic lupus erythematosus (SLE), polymyositis, dermatomyositis, systemic sclerosis (SSc) (scleroderma),  and rheumatoid arthritis.  MCTD can range from treatable illness to potentially life-threatening disease that may involve the lungs, kidneys, gastrointestinal system, or central nervous system.  Although MCTD can occur at any age, the average age of onset is 37-40 years,   and the disease is more prevalent in women than in men.  Early diagnosis is important because it may enable prevention of some of the more severe complications of MCTD, such as lung fibrosis.  However, diagnosis can be challenging because patients with MCTD may meet criteria for other connective tissue diseases or SARDs.   Diagnosis typically requires clinical examination, a thorough patient history, and laboratory testing for antinuclear antibodies (ANAs) as well as antibodies against U1 small nuclear ribonucleoprotein (anti-U1 RNP antibodies or anti-Smith/RNP antibodies). The presence of significantly elevated levels of anti-Smith/RNP (Sm/RNP) antibodies associated with the ANA speckled pattern, as detected by an indirect immunofluorescence antibody (IFA) assay, is a distinguishing characteristic of MCTD.   Laboratory testing in the initial workup for MCTD may also include autoantibody tests to help differentiate SARDs, serum immunoglobulin testing, and tests for other markers to evaluate systemic inflammation.

Quick Answers for Clinicians

What are the diagnostic challenges of mixed connective tissue diseases?

Individuals with mixed connective tissue disease (MCTD) may demonstrate symptoms associated with other connective tissue or systemic autoimmune rheumatic diseases (SARDs).  In addition, clinical characteristics of MCTD in a given patient may evolve over time, resulting in a change in diagnosis, or “clinical shift,” from MCTD to another SARD.   Some patients are considered to have undifferentiated connective tissue disease (UCTD), which is diagnosed when the patient’s signs and symptoms do not fulfill the classification criteria for any of the defined diseases. Over time, some patients with UCTD will also experience clinical shift and develop a specific SARD.  Long-term monitoring is recommended to follow the course of MCTD and UCTD and their possible evolution to other diseases.  See Monitoring section.

Which issues are important to keep in mind with antinuclear antibody testing?

Antinuclear antibodies (ANAs) alone are not specific for systemic autoimmune rheumatic diseases (SARDs); they are also seen in infections, malignancies, and even in healthy individuals.  ANA testing is most appropriate in cases of reasonable clinical suspicion for mixed connective tissue disease (MCTD) or another SARD.  For comprehensive information on ANA patterns and their clinical associations, refer to the International Consensus on ANA Patterns  website.

Is human leukocyte antigen testing indicated for mixed connective tissue disease?

Human leukocyte antigen (HLA) DRB1*04:01 and HLA*B08 have been determined to be risk alleles for mixed connective tissue disease (MCTD). Studies indicate that the HLA profiles are different in patients with MCTD compared with healthy patients and patients with similar systemic autoimmune rheumatic diseases (SARDs), such as systemic lupus erythematosus (SLE), polymyositis, and systemic sclerosis (SSc).  However, more research is needed to understand the contribution of HLA alleles to the pathogenesis of MCTD.  Other HLA associations include HLA-DR1 and HLA-DR2. 

Which testing algorithms are related to this topic?

Indications for Testing

Laboratory testing for MCTD is appropriate to:

  • Diagnose individuals who present with rheumatologic disease with overlap features
  • Monitor patients with an established diagnosis of MCTD for the presence of new antibodies that might indicate the evolution of MCTD to another connective tissue disease
  • Monitor patients with MCTD for disease progression, particularly lung disease

Criteria for Diagnosis

Various diagnostic criteria have been proposed for MCTD; however, only the Alarcón-Segovia criteria and the Kasukawa criteria have been regularly used.  To fulfill the Alarcón-Segovia criteria, patients must have significantly elevated anti-Sm/RNP antibody levels, in addition to three or more of the following signs and symptoms: edema of hands, synovitis, myositis, Raynaud phenomenon, and acrosclerosis.  The Kasukawa criteria have been used mostly in pediatric populations, and take into account additional findings such as lung and esophageal involvement. 

Laboratory Testing

Diagnosis

Autoantibody Testing

Antinuclear Antibodies

The presence of ANAs is a classic feature of SARDs ; therefore, ANA testing is a useful initial test for suspected MCTD. However, ANAs are not specific to SARDs and are also seen in infections and malignancies, and even in healthy individuals.  For that reason, ANA testing is best used for patients with a strong likelihood of MCTD or another SARD. 

ANA testing using the IFA test is considered the gold standard method for detecting these antibodies. ANA IFA test results are generally reported with patterns and associated titers.  Positive results for ANAs using solid-phase immunoassays (eg, enzyme-linked immunosorbent assays [ELISAs], multiplex bead assays) have limited utility for diagnosis because ANA patterns that may have relevant antigenic and disease associations can only be observed via IFA assays. Generally, the ANA patterns may help guide confirmatory testing for specific autoantibodies or may suggest the presence of a certain SARD in the absence of confirmatory tests. For comprehensive information on patterns and their clinical associations, refer to the International Consensus on ANA Patterns  website.

Extractable Nuclear Antigen Antibodies

Extractable nuclear antigens (ENAs) include more than 100 different soluble cytoplasmic and nuclear antigens. The most commonly used ENA tests include tests for Smith, Sm/RNP (or U1 RNP), SSA-52 (Ro52), SSA-60 (Ro60), SSB, Scl-70 (topoisomerase 1), and Jo-1 antibodies. These are usually the first-line tests following a positive ANA result. Thus, panels that test for specific ENAs can be helpful in the evaluation of SARDs.

Sm/RNP (U1 RNP) is an ENA associated with MCTD. Anti-Sm/RNP antibodies are a hallmark of MCTD and are found in the majority of patients with the disease.     Their presence can help to distinguish MCTD from other autoimmune diseases with similar clinical features, such as SLE, polymyositis, and SSc.  All major clinical criteria for MCTD require the presence of anti-Sm/RNP antibodies.  In addition, anti-Sm/RNP antibody levels have been reported to correlate with disease activity. 

Additional Specific Antibodies Associated with MCTD​

Based on the clinical features of MCTD, patients may present with other SARD-associated antibodies. These may include anti-double-stranded DNA (anti-dsDNA), anti-Smith, anti-SSA (anti-Ro), ribosomal-P, anticyclic citrullinated peptide (anti-CCP), rheumatoid factor (RF), anti-beta-2 glycoprotein 1 (anti-β2GPI), anticardiolipin (aCL), and antiendothelial cell antibodies.  

Other Tests

Additional laboratory tests might include a CBC to evaluate patients for mild anemia, leukopenia, and thrombocytopenia, which are common features in MCTD.  They also might include a C-reactive protein (CRP) test to detect inflammatory processes. If CRP testing is unavailable, erythrocyte sedimentation rate (ESR) testing can be used, but CRP is considered to be a more sensitive and specific test for acute phase inflammation. 

Monitoring

Lung Disease

Patients with MCTD should be monitored for the development of lung disease, one of the most serious complications of MCTD.   Lung disease in MCTD can take different forms, eg, interstitial lung disease (ILD) or pulmonary hypertension.  Early detection may slow or arrest the development of lung fibrosis and related complications.  Pulmonary function tests, such as diffusion capacity for carbon monoxide (DLCO) tests, can be used to assess lung function.

There is some evidence that serum levels of N-terminal pro-brain natriuretic peptide (NTproBNP) will be increased in patients with MCTD who develop pulmonary hypertension; therefore, NTproBNP testing may be helpful in patients with MCTD who have symptoms that suggest pulmonary hypertension. 

Clinical Shift

The clinical characteristics of MCTD in a given patient can change over time so that MCTD is eventually classified as a different SARD.   Termed “clinical shift,”  this disease evolution has been reported in up to 50% of patients with MCTD during the decade after diagnosis.  Some investigators have reported an association between particular antibodies and clinical shift from MCTD to other SARDs.  Long-term monitoring of patients with MCTD is recommended to assess disease course and possible progression to another connective tissue disease. 

ARUP Lab Tests

Initial ANA Tests for MCTD

Preferred ANA screening test for connective tissue diseases

If positive, patterns reported include homogeneous, speckled, centromere, nucleolar, nuclear dots, or cytoplasmic; all positive results are reported with endpoint titers

A negative test does not rule out the presence of connective tissue disease

Initial screening test for connective tissue diseases

Aids in initial diagnosis of connective tissue disease

ELISA may have lower sensitivity than IFA

If ANAs are detected by ELISA, then ANA, HEp-2, IgG by IFA will be added

For additional test information and limitations, refer to the Antinuclear Antibody (ANA) with HEp-2 Substrate, IgG by IFA with Reflex by Pattern Test Fact sheet

Detects antibodies against dsDNA, histones, SS-A (Ro), SS-B (La), Smith, Smith/RNP, Scl-70, Jo-1, centromere proteins, and other antigens extracted from the HEp-2 cell nucleus

Other Panel Tests Useful for MCTD

Aids in initial diagnosis of connective tissue diseases

Confirmatory test for specific and more common connective tissue diseases

Detects Smith (ENA), Smith/RNP, SSA, SSB, Jo-1, RPP, centromere and Scl-70 antibodies

Use to confirm a diagnosis of SLE or MCTD following a positive ANA result

Useful in the differential diagnosis of other connective tissue diseases, such as SSc, Sjögren syndrome, polymyositis, dermatomyositis, and overlap syndromes

If rheumatoid arthritis panel is positive, test reflexes to rheumatoid factors, IgA, IgG, and IgM, which may aid in prognostication

If CCP IgG ≥20 units and/or RF ≥15 IU/mL, then rheumatoid factor, IgG/IgM/IgA by enzyme immunoassay (EIA) will be performed

Detects CCP antibody, IgG; RF; RFs, IgA, IgG, and IgM by ELISA

Single Antibody Test for MCTD

Useful in the differential diagnosis of connective tissue diseases with or without myopathy

Primarily associated with a diagnosis of MCTD, but may be seen in patients with SLE, SSc, and inflammatory myopathies

Order as secondary screen based on results of ANA testing

Useful for Multiple Connective Tissue Diseases

Order as secondary screen based on results of ANA test or if ANA IFA is negative and Sjögren syndrome, SLE, SSc, or myositis are strongly suspected

Recommended first-line test for the evaluation of polymyositis or inflammatory myopathies

Useful to Differentiate Systemic Scleroderma/Sclerosis

Useful for diagnosis of SSc

Order as secondary screen based on results of ANA testing or based on suspicion for SSc

Preferred test is comprehensive SSc panel

Negative results do not rule out SSc

Comprehensive evaluation of systemic SSc

Indicated when suspicion for SSc is high and patient presents with features of overlap syndrome

For patients with distinct features of SSc, order the criteria systemic sclerosis panel

Detects ANA titer, ANA pattern, anti-Scl-70, anti-RNA polymerase III antibody, anti-Smith/RNP antibody, antifibrillarin (U3 RNP), anti-PM/Scl antibody

Indicated for patients with distinct features of SSC

For a more comprehensive panel that includes U3 RNP, PM/Scl-100, and U1 RNP, refer to the comprehensive systemic sclerosis panel

Useful for diagnosis of SSc

Negative results do not rule out SSc

Preferred test is comprehensive SSc panel

Useful to Differentiate SLE and/or Sjögren Syndrome

Confirmatory test for SLE based on ANA results

Secondary screening for SLE based on ANA results

Recommended for the differential diagnosis of SLE and Sjögren syndrome

Detects Smith/RNP (ENA) antibody, IgG; Smith (ENA) antibody, IgG; SSA 52 and 60 (Ro) (ENA) antibodies, IgG; SSB (La) (ENA) antibody, IgG

Recommended for the differential diagnosis of SLE and Sjögren syndrome

Order as secondary screen based on suspicion for SLE and Sjögren syndrome

Preferred panel (extractable nuclear antigen antibodies) contains SSA 52, SSA 60, and SSB

May be used in detecting central nervous system SLE (somewhat rare) or renal involvement in SLE

Not specific for SLE (eg, detected in autoimmune hepatitis [AIH])

Useful for Monitoring in MCTD

Aid in diagnosis, prognosis, and management of acute and chronic heart failure

May be helpful in patients with MCTD who have symptoms that suggest pulmonary hypertension

Medical Experts

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References

  1. Nuclear Patterns ICAP

    International Consensus on Antinuclear Antibody Patterns. Nuclear Patterns. International Consensus on ANA Patterns. Gainesville, FL. [Updated: 2019; Accessed: Feb 2020]

    Online
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