Mixed Connective Tissue Disease (MCTD) in a Girl with Lower Extremities Edema: A Brief Report.

Background: Mixed Connective Tissue Disease (MCTD) is a rare condition in children, characterized by a high titer of anti-ribonucleoprotein-U1 (anti-U1 RNP) antibodies, often presenting with overlapping features of two or more rheumatologic disorders, including juvenile idiopathic arthritis (JIA), systemic lupus erythematous (SLE), systemic sclerosis (SSc), and juvenile dermatomyositis/polymyositis (JDM/PM).

Case presentation: We report the case of an 8-year-old girl with a history of fever, hair loss, lower extremities edema, weakness, oral aphthous ulcers, and a high titer of anti-U1 RNP antibodies, which is consistent with the diagnosis of MCTD. The patient received immunomodulator drugs, and her disease went into remission.

Conclusion: Diagnosing MCTD in pediatric patients can be challenging. It should be considered especially in cases with recurrent muscular weakness or pain, lupus-like manifestations, and edema. Moreover, serum anti-U1 RNP testing can be a helpful diagnostic tool.