Laboratory and Imaging Studies
Laboratory tests
Obtain a white blood cell (WBC) count and differential, which are crucial when determining the degree of granulocytopenia. Studies show that the greatest risk for infection is a granulocyte count lower than 1000/µL. It must be kept in mind, however, that the level of neutropenia varies over time without medical intervention. Granulocyte dysfunction and an absolute decrease in the number of granulocytes may predispose to infection.
Anemia and thrombocytopenia may result from hypersplenism. Anemia of chronic disease may result from the underlying inflammatory disease.
Mild elevations of alkaline phosphatase and transaminase levels may occur.
Some 98% of patients with Felty syndrome (FS) have high titers of rheumatoid factor (RF). This is because extra-articular manifestations of rheumatoid arthritis (RA) are strongly associated with RF.
Antinuclear antibodies (ANAs), found in 67% of cases; antihistone antibodies; and even antineutrophil cytoplasmic antibodies (perinuclear pattern; p-ANCA), found in 77% of cases, commonly occur in patients with Felty syndrome. The significance of autoantibodies in Felty syndrome is unknown, and their contribution, if any, to the disease itself is uncertain.
Erythrocyte sedimentation rate (ESR) and serum immunoglobulin levels are invariably elevated in patients with FS. Cryoglobulins may be present.
Diagnostic imaging
Radionuclide studies, ultrasonography, or computed tomography (CT) may define the presence and extent of splenomegaly. The same modalities can also be used to assess patient response to therapy.
Histologic Findings
Bone marrow aspiration and biopsy are especially important to rule out large granular lymphocytosis (LGL). The bone marrow of patients with FS shows adequate megakaryocytes and myeloid hyperplasia with arrested development at the level of immature cell forms.
An unusual type of liver involvement known as nodular regenerative hyperplasia is associated with FS. This condition is characterized by mild portal fibrosis or lymphocyte and plasma cell infiltration but is not typical of cirrhosis. It may be complicated by portal venule occlusion and regenerative nodule formation.
