Mixed Connective-Tissue Disease

Updated: Oct 01, 2018
  • Author: Eric L Greidinger, MD; Chief Editor: Herbert S Diamond, MD  more...
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Overview

Practice Essentials

Mixed connective-tissue disease (MCTD) was first recognized by Sharp and colleagues (1972) in a group of patients with overlapping clinical features of systemic lupus erythematosus (SLE), scleroderma, and myositis, with the presence of a distinctive antibody against what now is known to be U1-ribonucleoprotein (RNP). [1, 2]

MCTD has since been more completely characterized and is now recognized to consist of the following core clinical and laboratory features [3, 4] :

Nevertheless, whether MCTD is a distinct disease entity has been in question since shortly after its original description. A minority of authors continue to suggest that MCTD represents subgroups or early stages of disorders such as systemic lupus erythematosus (SLE) or systemic sclerosis, or an overlap syndrome. [6] Ciang and colleagues propose that MCTD would more accurately be termed undifferentiated autoimmune rheumatic disease. [7]

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Pathophysiology

Pathophysiologic abnormalities that are believed to play a role in MCTD include the following:

  • B-lymphocyte hyperactivity, resulting in high levels of anti–U1-RNP and anti–U1-70 kd autoantibodies
  • T-lymphocyte activation, with anti–U1-70 kd–reactive T lymphocytes circulating in the peripheral blood
  • Apoptotic modification of the U1-70 kd antigen
  • Immune response against apoptotically modified self-antigens
  • Genetic association with major histocompatibility genes human leukocyte antigen (HLA)–DRB1*04/*15 [8]
  • Vascular endothelial proliferation with widespread lymphocytic and plasmacytic infiltration of tissues
  • Activation of Toll-like receptors in a pattern that may differ from that of SLE

In a study of a nationwide MCTD cohort in Norway, Flåm and colleagues found that HLA-B*08 and DRB1*04:01 were risk alleles for MCTD, while DRB1*04:04, DRB1*13:01 and DRB1*13:02 were protective. Risk alleles for SLE, systemic sclerosis, and polymyositis/dermatomyositis were distinct from those for MCTD. [9]

Over time, some patients with MCTD also develop anti-Sm autoantibodies—an expansion of the autoimmune response known as epitope spreading. Escolà-Vergé reported that epitope spreading occurred in 13 (43%) of 40 patients with MCTD, mainly during the first 2 years after diagnosis.Compared with patients who did not have epitope spreading, patients Patients with epitope spreading had  significantly lower prevalence of skin sclerosis (0% vs. 44%, P = 0.004) and a higher prevalence of interstitial lung disease (46% vs. 15%, P = 0.05). [10]

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Etiology

The fundamental cause of MCTD remains unknown. Autoimmunity to components of the U1-70 kd snRNP is a hallmark of disease. Anti-RNP antibodies can precede overt clinical manifestations of MCTD, but overt disease generally develops within 1 year of anti-RNP antibody induction.

The loss of T-lymphocyte and B-lymphocyte tolerance, due to cryptic self-antigens, abnormalities of apoptosis, or molecular mimicry by infectious agents, and driven by U1-RNA-induced innate immune responses, are proposed current theories of pathogenesis.

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Epidemiology

United States

A population-based study from Olmsted County, Minnesota found that MCTD occurred in about 2 persons per 100,000 per year. Diagnosis was frequently delayed, with a median of 3.6 years elapsing from first symptom to fulfillment of diagnostic criteria. [11] A study in American Indian and Alaska Native adults found a  prevalence of 6.4 per 100,000 (95% confidence interval 2.8-12.8). [12]

International

In an epidemiological survey in Japan, MCTD has a reported prevalence of 2.7 cases per 100,000 population. [13] A population-based study in Norway found the point prevalence rate to be 3.8 cases per 100,000 adult population, with a female-to-male ratio of 3.3, and an annual incidence rate of  2.1 per million. [14]  

Mortality/Morbidity

Long-term outcome studies have established pulmonary hypertension as the most common disease-related cause of death. [15] Immunoglobulin G (IgG) anticardiolipin antibodies are a marker for development of pulmonary hypertension. Infections are also a major cause of death.

Cardiac disease, most often pericarditis, is also common in MCTD patients, with prevalence estimates ranging from 13% to 65%. Other cardiac abnormalities include conduction abnormalities, pericardial effusion, mitral valve prolapse, diastolic dysfunction, and accelerated atherosclerosis. In three prospective studies with 13-15 years of follow-up, MCTD patients had an overall mortality rate of 10.4%, and 20% of these deaths were directly attributable to cardiac causes. [16]

Race-, Sex-, and Age-related Variances

MCTD has been reported in all races. The clinical manifestations of MCTD are similar among various ethnic groups; however, one study observed ethnic differences in the frequency of end-organ involvement. [17]

MCTD is far more common in females than in males. Estimates of the female-to-male ratio vary from approximately 3:1 to 16:1. [14, 13]

The onset of MCTD is typically at 15-25 years of age, but can occur at any age.

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Prognosis

Most patients with MCTD have a favorable outcome. Cases of MCTD with typical clinical or serologic features occasionally evolve into scleroderma, SLE, or another rheumatic disease.

Pulmonary hypertension is the most common disease-associated cause of death. Careful monitoring and aggressive treatment may improve the outcome of pulmonary hypertension. 

A long-term observational nationwide cohort study from Norway found that interstitial lung disease (ILD) was present in 41% of MCTD patients and progressed in 19% of patients across the observation period of a mean of 6.4 years. [18] The following were the strongest predictors of ILD progression:

  • Male sex  (hazard ratio [HR] = 4.0, 95% confidence index [CI]: 1.4, 11.5; P = 0.011)
  • Presence of anti-ro52 antibodies (HR = 3.5, 95% CI: 1.2, 10.2; P = 0.023)
  • Elevated anti-RNP titer (HR 1.5, 95% CI: 1.1, 2.0; P = 0.008)
  • Absence of arthritis (HR = 0.2, 95% CI: 0.1, 0.6; P = 0.004) 

 

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