musculoskeletal and connective tissue disorders
Mixed Connective Tissue Disease (MCTD)
Diagnosis of MCTD
Testing for antinuclear antibodies (ANA), antibodies to extractable nuclear antigen (antibodies to U1 ribonucleoprotein, or RNP), and Smith (Sm) and anti-DNA antibodies Organ involvement determined as clinically indicated MCTD should be suspected when additional overlapping features are present in patients appearing to have Diagnosis (SLE), Tests for ANA and antibody to U1 RNP antigen are done first. Almost all patients have high titers of fluorescent ANA that produce a speckled pattern. Antibodies to U1 RNP are present, usually at very high titers. Antibodies to the ribonuclease-resistant Sm component of extractable nuclear antigen (anti-Sm antibodies) and to double-stranded DNA (negative in MCTD by definition) are measured to exclude other disorders. The presence of anti-RNP antibodies is not sufficient to make the diagnosis of MCTD; typical clinical findings are also required. Rheumatoid factors are frequently present, and titers may be high. The erythrocyte sedimentation rate is frequently elevated. Diagnosis should be detected as early as possible with pulmonary function testing and echocardiography. Further evaluation depends on symptoms and signs; manifestations of myositis, renal involvement, or pulmonary involvement prompt tests of those organs. Creatine kinase, MRI, electromyogram, or muscle biopsy can help confirm the presence of myositis as part of MCTD. 