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Mixed Connective Tissue Disease (MCTD)

Mixed connective tissue disease (MCTD) is a rare disorder, that shows features of rheumatoid arthritis, SLE, polymyositis and systemic sclerosis and that is characterized by anti-ribonucleoprotein antibodies in high titre.
The clinical picture is variable and changes over time, often towards the clinical picture of systemic sclerosis.
Most patients are women aged 30-40 years.

Almost all patients have arthritis or arthralgia
Sausage-like swelling of the fingers (pictures F1 F2) and Raynaud's phenomenon (picture F3); some patients also develop finger ulcers
Skin changes resembling those seen in SLE
Muscle symptoms, which resemble those seen in polymyositis
Of pulmonary changes, interstitial lung disease (ILD) is the most common and one of the most severe manifestations of MCTD.
- Symptoms include cough, exercise dyspnoea and reduced performance.
An increase in pulmonary arterial pressure Increased Pulmonary Blood Pressure: Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension rarely occurs.
Pleuritis, carditis and nephritis occur but are more common in SLE

Full blood count, ESR, CRP, chemical urinalysis, plasma creatinine, creatine kinase, ALT, ALP, serum antinuclear antibodies, rheumatoid factor
Anaemia, leucopenia and thrombocytopenia are common findings.
ESR is usually elevated, but CRP concentration may be normal or slightly elevated.
Speckled pattern of anti-nuclear antibodies is a typical finding
The diagnosis is made within specialized care.
- E.g. determination of antibodies against extractable nuclear antigens (ENA), in which antibodies reacting with nuclear ribonucleoprotein are found
- In addition to these antibody tests, early investigations include lung HRCT, ECG, proBNP and, if necessary, different specialist consultations.

Non-steroidal anti-inflammatory drugs and antirheumatic drugs (not sulfasalazine) for arthritis
- Sulfa-containing preparations can sometimes exacerbate the activity of systemic rheumatic diseases (mainly SLE) and are therefore not recommended in MCTD either.
Small-dose glucocorticoids for general symptoms
Large-dose glucocorticoids for severe organ manifestations
As in SLE, treatment should be adjusted according to the clinical picture.

In the early stage of the disease, follow-up is done in specialized care.
If no visceral changes (lung, heart, kidney changes) are detected and if other symptoms subside with initial medication or without medication, follow-up can be transferred to primary care within 1-2 years.
Treatment and follow-up of visceral manifestations is carried out in specialized care in collaboration with other specialties, according to individual assessment.
- If the patient's situation subsequently calms down, the follow-up can be transferred to primary care in the future.
Recommended follow-up examinations in primary care every 1-2 years
- Basic tests such as basic blood count with platelet count, ALT, plasma creatinine, chemical screening of urine
- If needed, ECG (in case of exercise dyspnoea, reduced performance, chest sensations)
- No need to monitor antibodies

Very much depends on the organ manifestations.
ILD or increased pulmonary arterial pressure worsen the prognosis, and they are associated with increased mortality.
If the patient does not develop any organ damage, the prognosis is quite good.

Boleto G, Reiseter S, Hoffmann-Vold AM, et al. The phenotype of mixed connective tissue disease patients having associated interstitial lung disease. Semin Arthritis Rheum 2023;63():152258 [PubMed]
Gunnarsson R, Hetlevik SO, Lilleby V, et al. Mixed connective tissue disease. Best Pract Res Clin Rheumatol 2016;30(1):95-111 [PubMed]