Felty syndrome (FS) is a rare but serious complication that can develop in individuals who have long-standing, often severe, Rheumatoid Arthritis (RA). This condition represents an extra-articular manifestation of RA, meaning it involves parts of the body outside of the joints, specifically affecting the immune and hematological systems. FS occurs in a small percentage, perhaps 1% to 3%, of all RA patients, typically appearing after years of active joint disease.
The Defining Triad
Felty syndrome is classically characterized by the presence of three specific medical components, referred to as the triad: Rheumatoid Arthritis, splenomegaly, and neutropenia. This combination of conditions distinguishes FS from uncomplicated RA. The underlying RA is typically severe and seropositive, meaning the patient tests positive for high levels of rheumatoid factor.
Splenomegaly is an abnormal enlargement of the spleen. The spleen is responsible for filtering blood and removing old or damaged blood cells. In Felty syndrome, the enlarged spleen can become hyperactive, leading to the third, and most significant, component of the triad.
Neutropenia is defined as an abnormally low count of neutrophils, a specific type of white blood cell. Neutrophils are the body’s primary defense against bacterial and fungal infections, and their low count is the most critical aspect of FS. The enlarged spleen contributes to neutropenia by sequestering and destroying too many neutrophils, while the underlying autoimmune process also interferes with their production in the bone marrow.
Recognizable Signs and Systemic Manifestations
Severe neutropenia compromises the body’s ability to mount an effective defense against pathogens. Patients often experience recurrent and severe bacterial infections, particularly affecting the skin, mouth, and respiratory tract, such as pneumonia. These infections can become life-threatening and are a major cause of illness and death in people with FS.
Systemic symptoms like fever, unexplained weight loss, and general malaise are common. Some individuals may also develop leg ulcers that are slow to heal, often related to vasculitis. Other potential manifestations include the presence of rheumatoid nodules, which are lumps under the skin, and an enlarged liver or lymph nodes.
Confirming the Diagnosis
The confirmation of Felty syndrome requires a combination of laboratory tests and imaging studies. A Complete Blood Count (CBC) with differential is an essential first test, as it confirms the presence of neutropenia, typically showing an absolute neutrophil count (ANC) below 2,000 cells per microliter. Further blood work usually confirms the seropositive nature of the underlying RA through high titers of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies.
Imaging is necessary to establish splenomegaly. An abdominal ultrasound or a computed tomography (CT) scan is commonly used to visualize and measure the size of the spleen. A bone marrow examination may be performed to assess the production of blood cells and rule out disorders like large granular lymphocyte syndrome or myelodysplastic syndromes.
Treatment and Disease Management
Treatment for Felty syndrome is focused on controlling the underlying Rheumatoid Arthritis activity and directly managing the resulting neutropenia and infection risk. Managing the RA is often the first therapeutic step, as controlling the autoimmune inflammation frequently leads to an improvement in the neutrophil count and splenomegaly. Disease-Modifying Anti-Rheumatic Drugs (DMARDs), such as methotrexate, are the first-line treatment.
Pharmacological agents are used to increase the white blood cell count in patients with severe neutropenia or active infections. Granulocyte colony-stimulating factor (G-CSF) is a recombinant growth factor that stimulates the bone marrow to produce and release neutrophils into the blood. In cases of life-threatening infection, growth factors are administered quickly to raise the absolute neutrophil count.
If medical treatments fail to resolve severe neutropenia or recurrent infections, a splenectomy may be considered. This procedure removes the hyperactive organ that is destroying blood cells, often resulting in a significant and sustained increase in neutrophil counts. Aggressive treatment of infections with broad-spectrum antibiotics is initiated whenever an infection is suspected.