1. Serologic criterion: Positive antibodies to U1 RNP antibodies at a titer ≥1:1600

2. Clinical criteria:

1) Edema of the hands

2) Synovitis

3) Myositis

4) Raynaud phenomenon

5) Sclerodactyly

Diagnosis of MCTD: Fulfilled serologic criterion and ≥3 of the clinical criteria (coexisting edema of the hands, Raynaud phenomenon, and Sclerodactyly require an additional fulfillment of the criteria 2b or 2c).

1. Common symptoms:

1) Raynaud phenomenon

2) Swollen fingers or hands

2. Positive antibodies to U1 RNP

3. Mixed findings:

1) SLE-like findings:

a) Polyarthritis

b) Lymphadenopathy

c) Facial erythema

d) Pericarditis or pleuritis

e) Leukopenia or thrombocytopenia

2) SSc-like symptoms:

a) Sclerodactyly

b) Pulmonary fibrosis, restrictive pattern on pulmonary function tests, or reduced DLCO

c) Hypomotility or esophageal dilation

3) Polymyositis-like symptoms:

a) Muscle weakness

b) Raised serum creatine kinase levels

c) Myogenic pattern on electromyography

Diagnosis of MCTD: Presence of ≥1 common symptom, serologic criterion, and ≥1 from each group of the mixed findings (1, 2, 3).