Hidoc Bulletin

Mixed connective tissue disease (MCTD) is a unique systemic autoimmune disorder with an overlapping characteristic of at least two connective tissue diseases (CTD), including systemic lupus erythematosus (SLE), systemic sclerosis (SSc), polymyositis (PM), dermatomyositis (DM), and rheumatoid arthritis (RA), as well as the presence of a distinct antibody, anti-U1-ribonucleoprotein (RNP) previously known as an antibody to extractable nuclear antigen (ENA). MCTD has no distinguishing clinical symptoms, and clinical presentations vary from person to person. 
 
Etiology:

The pathogenesis of mixed connective tissue disease is unknown. So far, no clear risk factor has been discovered. Environmental factors are likely to play a role in immune activation in those with genetic susceptibility. Certain viruses and chemicals have been linked to the disorder.

Epidemeology:

Mixed connective tissue disease is an uncommon disease with an unknown frequency. The occurrence of MCTD was 1.9 per 100,000 individuals per year in population-based research conducted in Olmsted County, Minnesota. The average age of diagnosis was 48 years, and 84% of those affected were female. The occurrence of MCTD was found to be 2.1 per million per year in a study of the Norwegian population. The female-to-male-to-male was 3.3 to 1, and the average age at diagnosis was 37.9 years. All races are infected by this illness, and all ethnic groups experience similar clinical symptoms.

Pathophysiology:

Since mixed connective tissue disease is characterized by the presence of anti-U1-RNP antibodies, it is presumed that anti-U1-RNP and its antigen are involved in the pathogenesis of MCTD. An intranuclear protein called the U1-RNP complex transforms pre-mRNA into mature RNA. It consists of the A, C, and 70 kDa proteins, which anti-U1 RNP antibodies bind to. The anti-RNP antibody in MCTD mostly targets the 70kDa antigen. There are links between environmental factors and the occurrence of MCTD, including infections, medications, toxins, Uv exposure, and pollutants like vinyl chloride and silica.

Diagnosis:

As it is a mixed connective tissue disorder different tests according to the occurrence of the disorder are done as follows:
Complete blood count - Demonstrates anemia and leukopenia in almost 75% of patients.
Chest X-ray - Helps in the evaluation of pulmonary infiltrates, pleural effusion, and cardiomegaly.
X-ray joints – X-rays of affected joints reveal rare periarticular osteopenia and aseptic necrosis may be found.
Echocardiogram - Pericardial effusion, mitral valve prolapses, left ventricular hypertrophy, and changes secondary to pulmonary hypertension.

Treatment:

Corticosteroids - Prednisone is one drug that can help decrease inflammation and inhibit your immune system from attacking healthy cells.
Antimalarial drugs - Mixed connective tissue disease can be treated with hydroxychloroquine which may also help to avoid flare-ups.
Calcium channel blockers – Nifedipine and Amlodipine relax muscles in the walls of blood vessels. 

Pulmonary hypertension medications - Bosentan or Sildenafil might be prescribed. Nonsteroidal anti-inflammatory drugs - These medications, such as ibuprofen or naproxen sodium might help relieve the pain and inflammation if your condition is mild.