Phenotypic variability in a child with Felty's syndrome: a case report

Felty's syndrome (FS) is characterized by the triad of rheumatoid arthritis (RA), splenomegaly and neutropenia. The arthritis is typically severe and virtually always associated with high-titer rheumatoid factor. The presence of persistent neutropenia is generally required to make the diagnosis. Most patients diagnosed with FS are aged 50-70 years and have had RA for more than 10 years. It is rarely seen in patients with juvenile idiopathic arthritis (JIA), with only five cases having been reported throughout the world.

The present study describes the case of a 14-year-old female with a seven-year history of polyarticular JIA, presenting with splenomegaly, hepatomegaly, cholestasis and thrombocytopenia. However, she occasionally developed neutropenia. Titers of rheumatoid factor and anti-CCP were persistently high, and the antinuclear antibody titer was 1:320, while the antibody results for anti-dsDNA and anti-Sm were negative. Serum levels of IgA, IgG, IgM and IgE were all persistently elevated, and the ratio of CD19⁺ lymphocytes in the subgroups of lymphocytes was persistently high. The level of complements was normal. No STAT3 and STAT5B mutations were found by next-generation sequencing. The patient did not respond to methotrexate, prednisolone, hydroxychloroquine (HCQ), sulfasalazine and etanercept but was responsive to rituximab.

JIA, thrombocytopenia and splenomegaly are the most common and important features in six children with FS, while persistent neutropenia is not seen in all these patients. No complement deficiency has been found in children with FS so far. Manifestations of FS without neutropenia may be extremely rare. There are differences between adults and children in the clinical and laboratory features of FS.