Is Mixed Connective Tissue Disease A Rare Disease?

Is Mixed Connective Tissue Disease A Rare Disease?

Yes, mixed connective tissue disease (MCTD) is a rare auto immune disease the incidence is approximately 2/100,000 annually commonly seen in women (M: F – 1:9) and the mean age of onset is 10-29 years.

The exact etiology is not clear however, the pathophysiology is believed to be due to an autoimmune reaction. The body produce increased number of antibodies probably due to the hyperreactive B and T lymphocytes. These antibodies bind to different cells and damage the cells which gives rise to the clinical features. The antibody that is commonly associated with mixed connective tissue disease is uroporphyrin isomerase ribonucleoprotein (UI-RNP).

A population-based study done in Norway had a total of 147 patients with mixed connective tissue disease and 113 were females, the female to male ratio is 3.3. The point prevalence rate of mixed connective tissue disease in Norway is 3.8 cases per 100,000 adult population and the annual incidence rate is about 2.1 per million. The common clinical manifestations reported were Raynaud’s phenomenon (99%), swollen hands (93%), arthritis (79%), and esophageal dysmotility (50%). Fifteen patients in the study were diagnosed before 18 years of age, there were 4 patients who were aged 9 years when they were diagnosed with mixed connective tissue disease. The remaining 132 patients had adult-onset mixed connective tissue disease and the mean age of diagnosis was 37.9 years. Most of the adult patients had their initial symptom at a mean age of 31.5 years and they were diagnosed with mixed connective tissue disease at a mean age of 35.1 years.

A population-based study in Olmsted County, Minnesota carried out on 50 patients with incident mixed connective tissue disease from 1985 to 2014 showed that mixed connective tissue disease occurred in about 2 persons per 100,000 per year. 84% of the patients with mixed connective tissue disease were females. The standard mortality ratio was 1.1 and it was not much of a difference when compared to the general population. The most common initial symptoms were Raynaud’s phenomenon (50%), then arthralgia (30%) and thirdly swollen hands (16%). The diagnosis was delayed about 3.6 years after the initiation of the first symptom. Evolution into other connective tissue disorders occurred infrequently with 10-year rate of evolution of 8.5% in systemic lupus erythematosus and 6.3% in systemic scleroderma

A study done on American Indian and Alaska Native adults showed the prevalence is 6.4 per 100,000. An epidemiological survey carried in Japan revealed the mixed connective tissue disease prevalence is 2.7 cases per 100,000 populations.

The prevalence in children is abut 0.3% of pediatrics rheumatology patients, its very rare in children compared to the adults. Median age of onset is about 11 years it can range from 2-16 years. Even in children it’s more common in females the ratio is about 1:6.

The prognosis of mixed connective tissue disease has a favorable outcome. Most of the cases with typical clinical features and serologic investigations occasionally transfer into scleroderma, systemic lupus erythematosus or rheumatic disease. Mixed connective tissue disease related death occurs most commonly due to pulmonary hypertension. Anticardiolipin antibodies and lupus anticoagulant are markers of pulmonary hypertension. Pericarditis is also another cause of death (13-65%). Other cardiac abnormalities such as conduction abnormalities, pericardial effusion, mitral valve prolapse, diastolic dysfunction, and accelerated atherosclerosis also can cause death. In three prospective studies with MCT patients followed-up for 13-15 years had an overall mortality rate of 10.4% and 20% of these deaths were due to cardiac problems

Conclusion

Yes, mixed connective tissue disease (MCTD) is a rare auto immune disease the incidence is approximately 2/100,000 annually commonly seen in women (M: F – 1:9) and the mean age of onset is 10-29 years. A population-based study done in Norway had a total of 147 patients with mixed connective tissue disease and 113 were females, the female to male ratio is 3.3. The point prevalence rate of MCTD in Norway is 3.8 cases per 100,000 adult population and the annual incidence rate is about 2.1 per million. A population-based study in Olmsted County, Minnesota carried out on 50 patients with incident mixed connective tissue disease from 1985 to 2014 showed that MCTD occurred in about 2 persons per 100,000 per year. A study done on American Indian and Alaska Native adults showed the prevalence is 6.4 per 100,000. An epidemiological survey carried in Japan revealed the mixed connective tissue disease prevalence is 2.7 cases per 100,000 populations.

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