Reiter syndrome: Year of the Zebra

Reactive arthritis, formerly known as Reiter syndrome, is a rare autoimmune condition primarily affecting the joints, which develops in response to an infection in another part of the body. Typically, the infection affects the genitourinary or gastrointestinal tract, although it can often go unnoticed by the individual.

The immune system reacts to the infection’s causative agent, usually a bacteria, and due to structural similarities between the bacteria and the body’s tissues, the immune system mistakenly attacks the body’s tissues.

Reactive arthritis is more common in individuals who are positive for the HLA-B27 gene, a genetic marker that increases susceptibility to certain inflammatory conditions like psoriasis and ankylosing spondylitis.

Symptoms of reactive arthritis often start several days to three weeks following a genitourinary or gastrointestinal infection. The main symptom is usually pain and swelling of a single, large joint like the knee. Less often, it involves other joints like the ankles, hips, and smaller joints in the feet; or affect multiple joints. There can also be inflammation of tendons where they connect to bone, called enthesitis; as well as inflammation of the fingers, called dactylitis, also known as “sausage fingers.”

In addition to joint pain, individuals often develop symptoms in other parts of the body, notably the urethra and conjunctiva of the eyes. When the urethra is involved, it can lead to burning pain with urination; and when the conjunctiva is affected it causes inflammation, or conjunctivitis, which leads to redness of the eyes. Rarely, reactive arthritis can cause skin lesions affecting the palms and soles of the feet, as well as ulcers in the glans of the penis.

Reactive arthritis is often self-limiting and usually fades over the course of a year without causing any permanent joint damage or immobility. However, in a small percentage of individuals the condition may become chronic, with symptoms persisting after the acute phase.

There is no single definitive test for reactive arthritis. Ultimately, diagnosis is made clinically based on the history of a previous infection that may be associated with the development of the condition. In cases where the diagnosis is unclear, an arthrocentesis may be done to examine the synovial fluid, which is the fluid that surrounds joints.