Reactive arthritis, formerly known as Reiter's syndrome, is a condition that causes inflammation (redness and swelling) in various places in the body.
It usually develops following an infection, and in most cases clears up in a few months without causing long-term problems.
The three most common places affected by reactive arthritis are:
the joints (arthritis), which can cause pain, stiffnessand swelling
the eyes (conjunctivitis), which can cause eye pain and redness
the urethra (non-gonococcal urethritis), which can cause pain when urinating (the urethra is the tube that carries urine out of the body)
However, most people will not experience all of these problems.
What causes reactive arthritis?
Reactive arthritis usually develops within four weeks of an infection, typically after a sexually transmitted infection (STI) such as chlamydia, or an infection of the bowel.
For reasons that are still unclear, the immune system (the body's defence against infection) appears to malfunction in response to the infection and starts attacking healthy tissue, causing it to become inflamed.
Seeking medical advice
See your GP if you have swollen and painful joints, especially if you have recently had symptoms of an infection such as diarrhoea or pain when passing urine.
There is no single test for reactive arthritis, although blood and urine tests, genital swabs and X-rays may be used to check for infection and rule out other causes of your symptoms.
Your GP will also want to know about your recent medical history, such as whether you may have recently had a bowel infection or an STI.
How reactive arthritis is treated
There is currently no cure for reactive arthritis, but most people get better in around six months. Meanwhile, treatment can help to relieve symptoms such as pain and stiffness.
Symptoms can often be controlled using non-steroidal anti-inflammatory drugs (NSAIDs) and painkillers such as ibuprofen.
Severe symptoms may require more powerful steroid medication (corticosteroids) or disease-modifying anti-rheumatic drugs (DMARDs).
Who is affected
Reactive arthritis can occur at any age, but it most commonly affects young adults aged 20-40.
Men are generally affected more than woman – particularly in cases linked to STIs, which are estimated to be about 10 times more common in men.
People who have a certain gene called HLA-B27, which is found in around one in every 10 people in the UK, are about thought to be around 50 times more likely to develop reactive arthritis than those who don't have this gene.
Preventing reactive arthritis
The most effective way to reduce your risk of reactive arthritis is to avoid the STIs and bowel infections that most commonly cause the condition.
The most effective way of preventing STIs is to always use a barrier method of contraception, such as a condom, during sex with a new partner.
Read advice on STIs, contraception and sexual health.
Ensuring good standards of hygiene when preparing and storing food can help to prevent gastrointestinal infections. Read about food safety and preventing food poisoning.
Causes of reactive arthritis
It's not known exactly what causes reactive arthritis, but it's thought to be the result of the immune system reacting to an infection.
The immune system
Your immune system is your body's defence against illness and infection. When it senses a virus or bacteria, it sends antibodies and cells to fight the infection. This causes tissues to swell, known as inflammation, which makes it harder for the infection to spread.
In cases of reactive arthritis, something goes wrong with the immune system and it causes inflammation in parts of the body that were not infected, often after the infection has already passed.
The two most common types of infection linked to reactive arthritis are:
sexually transmitted infections (STIs) – such as chlamydia or gonorrhoea, although many cases occur after non-gonococcal urethritis
infections of the bowel and digestive system (gastrointestinal infections) – usually caused by either campylobacter or salmonella bacteria, both of which can cause food poisoning
Research has shown that people with a specific gene known as HLA-B27 have a significantly increased chance of developing reactive arthritis, as well as related conditions such as ankylosing spondylitis (a type of arthritis that affects the spine).
In the UK, it's estimated that around 1 in every 10 people have the HLA-B27 gene. Around 3 out of every 4 cases of reactive arthritis develop in people with the gene.
People with the HLA-B27 gene also tend to have more severe and longer-lasting symptoms, with a greater risk of their symptoms recurring.
Exactly how the gene contributes to the development of reactive arthritis is unclear.
Treating reactive arthritis
There's no cure for reactive arthritis, but the condition is usually temporary and treatment can help to relieve your symptoms.
Most people will make a full recovery in about six months, although around one in five cases lasts a year or more, and a small number of people experience long-term joint problems.
There is also a risk you could develop the condition again after another infection.
In the initial stages of reactive arthritis, it's recommended that you get plenty of rest and avoid using affected joints.
As your symptoms improve, you should begin a gradual programme of exercise designed to strengthen affected muscles and improve the range of movement in your affected joints.
Your GP or specialist may recommend a suitable exercise programme for your arthritis. Alternatively, you may be referred to a physiotherapist for physical therapy.
You might also find ice packs and heat pads useful in reducing joint pain and swelling, although these should not be directly placed on your skin.
Antibiotics may not help to treat reactive arthritis itself, but they are sometimes prescribed if you have an ongoing infection – particularly if you have a sexually transmitted infection (STI). Your recent sexual partner(s) may also need treatment.
Non-steroidal anti-inflammatory drugs (NSAIDs)
Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, are the main medication used for reactive arthritis, as they can help to reduce inflammation and relieve pain.
However, taking a regular dose of a NSAID on a long-term basis can increase your risk of problems such as stomach ulcers. If you are at an increased risk of developing stomach ulcers, your GP may recommend an additional medication known as a proton pump inhibitor (PPI), which can protect your stomach by reducing the production of stomach acid.
Rarely, long-term use of NSAIDs can also slightly increase your risk of having a heart attack or stroke.
Steroid medication (corticosteroids) may be recommended if your symptoms don't respond to NSAIDs, or you're unable to use NSAIDs.
Steroids work by blocking the effects of many of the chemicals the body uses to trigger inflammation.
A corticosteroid called prednisolone is usually the preferred choice. Prednisolone can be given as an injection into a joint or as a tablet. Eye drops are also available if you have inflamed eyes (conjunctivitis).
Around 1 in 20 people who take prednisolone will experience changes in their mental state, such as depression or hallucinations. Contact your GP as soon as possible if you notice any changes in your thoughts or behaviour.
Other side effects can include weight gain, acne, stomach ulcers and osteoporosis, although these should improve as your dose is decreased.
Disease-modifying anti-rheumatic drugs (DMARDs)
If your symptoms persist despite treatment with NSAIDs and/or corticosteroids, you may be prescribed a medication known as a disease-modifying anti-rheumatic drug (DMARD).
Like corticosteroids, DMARDs work by blocking the effects of some of the chemicals your immune system uses to trigger inflammation.
It can take a few months before you notice a DMARD working, so it's important to keep taking medication even if you don't see immediate results.
A DMARD called sulfasalazine is usually the preferred option. Common side effects of sulfasalazine include feeling sick, loss of appetite and headaches, although these usually improve once your body gets used to the medication.
DMARDs may also cause changes in your blood or liver, so it's important to have regular blood tests while taking these medicines.