Anti-RNP antibody in a child with undifferentiated carcinoma and no evidence of mixed connective tissue disease.

We describe a young girl who presented with musculoskeletal symptoms and who was found to have high titres of antinuclear antibody with anti-RNP antibody. She was initially suspected of having mixed connective tissue disease, but ultimately was found to have metastatic undifferentiated carcinoma with an unknown primary site. This is a very uncommon malignancy of childhood and an association with anti-RNP antibody has, to our knowledge, not been described. The clinical significance of this finding is discussed. [ABSTRACT FROM PUBLISHER]