Reactive arthritis

Also called Reiter's syndrome

Joint inflammation triggered by an infection elsewhere, usually gut or genital, weeks earlier. Treating the trigger does not treat the arthritis.

What it is

Inflammation of joints triggered by an infection somewhere else in the body, typically one to four weeks earlier.

The usual triggers are gut infections, campylobacter, salmonella, shigella and yersinia, and genital infection with chlamydia. The joints themselves are not infected, which distinguishes it from septic arthritis and means antibiotics do not treat the arthritis, though the underlying chlamydia does need treating and partners need testing.

It usually affects a few large joints asymmetrically, most often knees, ankles and feet. It can also cause inflammation at tendon insertions, sausage-like swelling of a whole finger or toe, low back pain, eye inflammation and urinary symptoms.

It belongs to the spondyloarthritis family alongside ankylosing spondylitis and psoriatic arthritis, and is more likely in people carrying the HLA-B27 gene.

Most cases settle within three to twelve months. A minority become chronic.

The complication to know about is uveitis: a painful red eye with light sensitivity, which needs same-day eye assessment and can threaten sight.

Signs you might notice

Joint pain and swelling, usually asymmetric, in knees, ankles or feet, starting one to four weeks after an infection.

Heel pain, or pain where tendons attach to bone.

A whole finger or toe swollen like a sausage.

Low back and buttock pain, worse in the morning and better with movement.

Eye redness, pain and light sensitivity.

Urinary symptoms, discharge, or pain on passing urine.

Rash on the palms and soles, or mouth ulcers.

Fatigue and fever.

Same-day: a hot, swollen, very painful single joint with fever, which must be assumed to be septic arthritis until aspirated; or a painful red eye with light sensitivity.

How it can affect day-to-day life

The link to the earlier infection is frequently missed, because by the time the joints hurt the diarrhoea or the urinary symptoms are long forgotten. Asking about the preceding weeks is what makes the diagnosis.

Sexual health testing is part of the workup and is often skipped because of embarrassment on both sides. Untreated chlamydia perpetuates the problem and needs partner notification.

Being told a joint problem was caused by a sexually transmitted infection is difficult, and it needs handling carefully and accurately, since gut infections cause it just as often.

The fatigue is substantial and under-acknowledged.

Because most cases resolve, the treatment aim is symptom control and preserving function while waiting: anti-inflammatories, joint injections, and disease-modifying drugs for persistent disease.

Anybody in this family of conditions should know the uveitis symptoms and where their nearest eye casualty is.

Supporting someone well

Mention any infection in the preceding month: diarrhoea, or urinary or genital symptoms. That connection is the diagnosis.

Get sexual health testing, and make sure partners are tested and treated.

Treat a hot single joint as septic arthritis until it has been aspirated.

Learn the uveitis warning signs and go the same day for a painful red eye with light sensitivity.

Keep moving; rest stiffens the joints and worsens the outcome.

Ask for physiotherapy, particularly for the spine and heels.

Ask for rheumatology referral if it has not settled within a few months.

Ask about HLA-B27 testing and about the wider spondyloarthritis family if there is back pain or a family history.

Where to get help

A GP practice for assessment, and a sexual health clinic for testing.

Rheumatology for persistent disease.

Same-day eye assessment for a red painful eye; A and E for a hot swollen joint with fever.

Arthritis UK and the National Axial Spondyloarthritis Society for information on this family of conditions.