Osteoarthritis is the result of the wear and tear on joints. Rheumatoid arthritis, on the other hand, occurs when the immune system goes haywire and begins attacking joint linings. This chronic inflammatory condition also affects other tissue, but the joints are usually the most severely affected.

Here is what we know about the causes of rheumatoid arthritis.

What causes rheumatoid arthritis?

Although doctors aren't sure of the exact cause, it's thought that rheumatoid arthritis may result from a combination of genetics and environmental triggers. Some researchers believe an infection with a bacteria or virus can trigger the development of rheumatoid arthritis in someone who's genetically susceptible. However, to date, no infection or organism has been found that could be said to be the cause.

As rheumatoid arthritis develops, some of the body's immune cells recognize a protein as a foreign intruder. The exact protein is unknown and may be one of any number of potential candidates. Some of them are produced by infection, such as a viral, bacterial, or fungal infection. Other candidate proteins may have a genetic connection or stem from other causes.

Whatever the source, cells called lymphocytes react to this protein. The reaction then causes the release of cytokines, which are chemical messengers that trigger more inflammation and destruction. With rheumatoid arthritis, the main target of inflammation is the synovium, the thin membrane that lines the joints. The inflammation also spills to other areas in the body causing joint damage, inflammation, chronic pain, fatigue, and loss of function.

There are many cytokines, but the most important in rheumatoid arthritis are tumor necrosis factor (TNF) and interleukin-1. These cytokines are thought to trigger the process of joint damage in rheumatoid arthritis. Some treatments for rheumatoid arthritis aim to block these cytokines, reducing inflammation and joint damage.

What risk factors increase the chance of rheumatoid arthritis?

Rheumatoid arthritis is more common in women than in men. In fact, 70% of the patients with rheumatoid arthritis are women. In addition, there's an increased risk of rheumatoid arthritis in women who have never been pregnant and in those who have recently given birth.

Rheumatoid arthritis has a genetic link, and the disease can run in families. People with specific human leukocyte antigen (HLA) genes have a greater chance of developing rheumatoid arthritis than people who do not have the HLA genes. Still, not everyone with the HLA genes develops rheumatoid arthritis. In other words, genes can increase the risk of rheumatoid arthritis, but other unknown factors are also involved.

Older age and cigarette smoking may increase the risk of getting rheumatoid arthritis. So can stress. In fact, many patients with rheumatoid arthritis tell of having an extremely stressful life event within the six months before the disease appeared.

Symptoms of rheumatoid arthritis include joint pain, swelling, stiffness, and fatigue -- which can be mild or severe. Doctors recommend treating rheumatoid arthritis early, before there are visible signs of joint destruction.

WebMD Medical Reference

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Reviewed by Matthew Hoffman, MD on June 14, 2008

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Do You Have Fibromyalgia Pain?

Cymbalta is approved for the management of fibromyalgia.

Important Safety Information

Cymbalta^® (duloxetine HCl) is approved for the treatment of depression and generalized anxiety disorder, and for the management of diabetic peripheral neuropathic pain and fibromyalgia.

What should I talk about with my healthcare provider?

Patients on antidepressants and their families or caregivers should watch for new or worsening depression symptoms, unusual changes in behavior, thoughts of suicide, anxiety, agitation, panic attacks, difficulty sleeping, irritability, hostility, aggressiveness, impulsivity, restlessness, or extreme hyperactivity. Call your healthcare provider right away if you have thoughts of suicide or if any of these symptoms are severe or occur suddenly. Be especially observant within the first few months of antidepressant treatment or whenever there is a change in dose.

You should also know that:

Suicide is a known risk of depression and some other psychiatric disorders.
Antidepressants may increase suicidal thoughts or behaviors in some children, adolescents, and young adults especially within the first few months of treatment or when changing the dose. No increased risk has been shown for adults over age 24, and risk decreased for those over age 65.
All patients starting therapy should be monitored appropriately and observed closely for new or worsening depression symptoms, suicidal thoughts or behavior, or unusual changes in behavior.
Cymbalta^® is not approved for use in patients under age 18.

Who should NOT take Cymbalta?
You should not take Cymbalta if:

You have recently taken a type of antidepressant called a monoamine oxidase inhibitor (MAOI)
You have uncontrolled narrow-angle glaucoma (an eye disease)
You are taking Mellaril^® (thioridazine)

What other important information should I discuss with my healthcare provider?
Before starting Cymbalta, tell your healthcare provider:

about all of your medical conditions, including kidney problems, glaucoma, or diabetes
about your alcohol use
if you are taking nonprescription or prescription medicines, including those for migraine, to address a possible life threatening condition
if you are taking NSAID pain relievers, aspirin, or blood thinners. Use with Cymbalta may increase bleeding risk
if you are pregnant, plan to become pregnant during therapy, or are breastfeeding an infant

While taking Cymbalta, tell your healthcare provider:

if you have itching, right upper belly pain, dark urine, yellow skin/eyes, or unexplained flu-like symptoms, which may be signs of liver problems. Severe liver problems, sometimes fatal, have been reported
if you have high fever, confusion, and stiff muscles to address a possible life-threatening condition
before stopping Cymbalta or changing your dose
if you experience dizziness or fainting upon standing, especially when first starting Cymbalta or when increasing the dose. Your healthcare provider may periodically check your blood pressure while you are taking Cymbalta

If you have any questions, talk to your healthcare provider before taking Cymbalta.

What are the possible side effects of Cymbalta?

The most common side effect of Cymbalta was nausea. For most people who had it, the nausea was mild to moderate. Other common side effects included dry mouth, sleepiness, constipation, decreased appetite, and, increased sweating. This is not a complete list of side effects.

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