Felty syndrome is a rare complication of rheumatoid arthritis. People with the condition have an enlarged spleen, decreased white blood cell count, and recurrent infections.

Rheumatoid arthritis (RA) is an autoimmune and inflammatory disease that mainly attacks joints.

However, RA may also have other symptoms that affect other body parts beyond the joints. These are often severe complications of long-term inflammation relating to RA.

Felty syndrome is an uncommon complication of RA.

In this article, we cover Felty syndrome, including its causes, symptoms, treatment, and more.

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RA has two types: seropositive and seronegative. Seronegative RA generally has a poorer disease course and progress.

People with seropositive RA have high levels of rheumatoid factor and anti-citrullinated protein antibodies. In contrast, these antibodies are absent in people with seronegative RA.

Felty syndrome is a rare complication of seropositive RA. It involves the following:

  • chronic rheumatoid arthritis
  • enlarged spleen, which doctors call splenomegaly
  • neutropenia, or a low neutrophil count — neutrophils are a type of white blood cell

While the three symptoms typically characterize the condition, all three do not need to be present for a Felty syndrome diagnosis. However, neutropenia is a key feature of the condition and should be present.

Felty syndrome occurs in 1–3% of people with RA. However, its true prevalence may be lower due to the development of more effective treatments for RA.

The underlying cause of Felty syndrome is unclear. However, multiple factors, such as autoimmunity and genetics, likely play a role.

There is a strong link between Felty syndrome and RA with the genetic marker human leukocyte antigen-DR4 (HLA-DR4). This gene is present in over 90% of people with Felty syndrome. The presence of HLA-DR4 increases a person’s risk of having RA-related complications.

Experts also believe that Felty syndrome is an autoimmune disorder that occurs due to an allergy, blood disorder, or unknown immune disturbance.

The autoantibodies bind against neutrophils, trapping them and leading to neutropenia, a key feature of Felty syndrome.

Felty syndrome affects females three times more than males. The condition also affects more Caucasians than African Americans.

The syndrome tends to occur in people with a long-term and aggressive type of RA for over 10 years.

Felty syndrome manifests in people with severe RA, which is typically long term and severe.

Symptoms typically develop around 16 years after the initial onset of RA.

People with the condition do not usually experience symptoms other than recurrent infections due to low immunity. However, some may develop severe, life threatening infections.

Other symptoms of Felty syndrome include:

Doctors diagnose Felty syndrome by taking a detailed medical history and performing a thorough clinical evaluation.

Neutropenia is a hallmark feature of Felty syndrome. If a doctor suspects Felty syndrome, they will order a complete blood count.

An absolute neutrophil count of under 2,000 per microliter is necessary to diagnose someone with Felty syndrome.

Other lab tests that can help diagnose the condition include:

  • a rheumatoid factor test
  • cyclic citrullinated peptide antibody test
  • antinuclear antibodies
  • anti-histone antibodies
  • HLA-DR4

Imaging can also help detect the presence and extent of joint damage and spleen enlargement.

The doctor may also request a bone marrow biopsy to rule out large granular lymphocyte leukemia and non-Hodgkin lymphoma.

Treatments will aim to control a person’s underlying RA and treat neutropenia to reduce their risk of infections.

Long-term management of the underlying RA involves prescribing disease-modifying antirheumatic medications (DMARDs). These include:

  • methotrexate
  • hydroxychloroquine
  • sulfasalazine

If a person does not respond to DMARDs, the doctor may prescribe rituximab.

Doctors may also prescribe granulocyte colony-stimulating factor (G-CSF), which encourages the bone marrow to produce more white blood cells. Healthcare professionals recommend this treatment in people with a neutrophil count of less than 1,000 per microliter with severe, recurrent infections and who do not respond to DMARDs and rituximab.

A doctor will start a person on broad-spectrum antibiotics if they have an active infection.

Additionally, adequate oral hygiene and staying updated on vaccinations can help reduce a person’s risk of getting infections.

People with the condition who do not improve with conventional treatment may qualify for a splenectomy, an operation to remove the spleen.

Before the introduction of DMARDs, the 5-year mortality rate for Felty syndrome was 36%. There are no data on the outlook of the condition.

Treating the underlying RA should improve Felty syndrome in most people. However, without treatment, infections may occur, and the RA may worsen.

Advanced treatment options for RA gradually decrease the severity and presence of extra-articular manifestations, which are complications or symptoms that occur outside of affected joints. The use of G-CSF can also reduce the need for splenectomy.

Felty syndrome is a rare disease that occurs as a complication of RA. Chronic RA, splenomegaly, and neutropenia characterize the disease. However, a person may have Felty syndrome without having all these three conditions.

A low white blood cell count puts a person at risk of recurrent infections. Generally, Felty syndrome responds well to DMARDs and other conventional RA treatments. If symptoms do not improve, an individual may be a candidate for spleen removal.