Reactive arthritis

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

Terminology

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

Epidemiology

ReA most commonly occurs in males between age 15-35 ². It has an incidence of ~1 in 100 after enteric infections. 

Clinical presentation

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

• arthritis
• conjunctivitis
• urethritis (cervicitis in women) 

The following mnemonic can be used to remember the classic triad encountered in ReA: "Can't see, can't pee, can't climb a tree''.

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

Pathology

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

Aetiology

ReA occurs after 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

Radiographic features

Distal lower extremity involvement (MTP >> calcaneus > ankle > knee) 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).

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.

History and etymology 

The disease was originally named after Hans Reiter. However, recently this term has not been encouraged as he was a convicted Nazi war criminal who performed experiments of a new typhus vaccine that caused the death of hundreds of prisoners of war ⁹.

Treatment and prognosis

• tends to resolves after a few months in half of patients
• remaining patients have recurrent arthritis, tendinitis and fasciitis

Differential diagnosis

• psoriatic arthritis
  • ReA has different distribution with hand involvement, which is common in psoriatic arthritis, very uncommon ²
  • spondyloarthropathy and sacroiliitis are identical in both conditions
• disseminated gonococcal infection 
  • causes a septic arthritis c.f. sterile process of ReA