26th January 2024

Diagnosis 

In the early stages, differentiating MCTD from other autoimmune diseases, such as SLE and polymyositis, can be difficult. However, the most prominent initial features, such as puffy fingers, arthralgia and myalgia, should be further investigated by specific antibody testing, including ANA, ENA and Anti-U1 RNP.

One of the most widely used diagnostic criteria is that of the Alarcon-Segovia’s criteria, which has a sensitivity of 63% and a specificity of 86%. To fulfil the criteria, patients must have Anti-RNP antibodies with a hemagglutination titer of ≥1:1600 and three or more of the following clinical features (one of which must include myositis or synovitis): swollen hands, Raynaud’s phenomenon, acrosclerosis, synovitis and myositis.

The laboratory testing for MCTD hinges on the presence of the specific auto-antibodies, as mentioned previously, in particular ENA and Anti-U1 RNP. However, antibodies Sm, Ro, and La are occasionally, transiently seen in patients with MCTD.