Reactive arthritis (ReA) is a sterile inflammatory monoarticular or oligoarticular arthritis that follows an infection at a different site, commonly enteric or urogenital. It is classified as a type of seronegative spondyloarthropathy.

Terminology

Reactive arthritis was formerly known as Reiter syndrome or disease, which is the combination of urethritis, arthritis and conjunctivitis. Not all patients with reactive arthritis have Reiter syndrome (also see History and etymology below). 

Epidemiology

Reactive arthritis most commonly occurs in males between ages 15-35 ². It has an incidence of ~1 in 100 following enteric infections. 

Clinical presentation

Usually transient following infection and involving one or two large joints. The classical triad consists of:

• arthritis

• conjunctivitis

• urethritis (cervicitis in women) 

The following memory aides can be used to remember the classical triad encountered in reactive arthritis:

• "can't see, can't pee, can't climb a tree''

• "can't see, can't pee, sore knee''

Other extra-articular manifestations include cardiac conduction abnormalities and aortic regurgitation. 

Pathology

In reactive arthritis, there is joint inflammation, bone proliferation, periostitis, and enthesitis.

Aetiology

Reactive arthritis occurs following infections including ^5-8:

• enteric: Yersinia, Salmonella, Shigella, Campylobacter and less commonly enterotoxic Escherichia coli (ETEC)

• sexually-transmitted: Chlamydia trachomatis

• other: brucellosis

Markers

• HLA B27 positive in ~80% of patients

• a proportion of patients have serum rheumatoid factor ¹⁰

Radiographic features

Distal lower extremity involvement (knee > metatarsophalangeal joints > calcaneus > ankle > sacroiliac joints) is more prevalent than upper extremity involvement. It affects hands, wrists, and feet with a distribution that is unilateral or bilateral and asymmetric (it becomes symmetric in later stages).

Enthesitis may develop at the calcaneus at the sites of Achilles tendon and plantar fascia attachment.

A large bulky paravertebral area of ossification "floating osteophyte" is often seen.

It can have a very similar appearance to psoriatic arthritis with the classic features of ill-defined erosions, enthesopathy, bone proliferation, early juxta-articular osteoporosis, uniform joint space loss and fusiform soft tissue swelling ².  

Both psoriasis and reactive arthritis can cause a sacroiliitis, which is usually asymmetric ³.

Treatment and prognosis

• tends to resolve after a few months in half of patients

• remaining patients have recurrent arthritis, tendonitis and fasciitis

History and etymology 

The disease was originally named after Hans Reiter (1881-1969) a german bacteriologist. However, this term has been discouraged as he was a convicted Nazi war criminal who was involved in the sterilisation of thousands of individuals in a misguided attempt to prevent the transmission of "inferior genes" as well as authorising the use of an experimental typhus vaccine that caused the death of at least 250 prisoners of the Buchenwald concentration camp ^9,12.

Differential diagnosis

• psoriatic arthritis

  • reactive arthritis has a different distribution; hand involvement is very uncommon, while common in psoriatic arthritis ²

  • spondyloarthropathy and sacroiliitis appear identical in both conditions

• disseminated gonococcal infection 

  • causes septic arthritis, cf. sterile process of reactive arthritis