Fibromyalgia vs rheumatoid arthritis

What the research found.

• In the EULAR recommendations for fibromyalgia, aerobic and strengthening exercise has the top evidence rating. It rates above cognitive behavioral therapy, above multi-part therapies, above acupuncture and hydrotherapy, and above every drug in the set. So the best-backed treatment there sits outside the pharmacy.

  Macfarlane and colleagues, Annals of the Rheumatic Diseases, 2017

• Tai chi beat aerobic exercise in fibromyalgia over 24 weeks, at matched intensity and length. Across all the tai chi groups combined, the fibromyalgia impact questionnaire improved by 5.5 points more, from 0.6 to 10.4. The group doing tai chi twice a week for the full 24 weeks improved by 16.2 points more, from 8.7 to 23.6.

  Wang and colleagues, BMJ, 2018

• Anti-CCP cleared 95 percent of the people who didn't have rheumatoid arthritis, at a likelihood ratio of 12.46 for a positive result. There's no matching antibody test for fibromyalgia, because no antibody is involved to look for. So a positive result points one way and a negative one settles nothing.

  Nishimura and colleagues, Annals of Internal Medicine, 2007

• One review covered 22 studies of nutrition in fibromyalgia, which between them tested 17 different things. Its authors concluded there's not enough evidence to recommend any one of them. So the honest answer on diet here is that nothing at all is established, which is worth saying plainly.

  Lowry and colleagues, Nutrients, 2020

• At the first measurement, more than a third of rheumatoid arthritis patients had one normal or negative result. That meant a normal sedimentation rate, a normal C-reactive protein, or a negative rheumatoid factor. So normal blood work doesn't separate the two on its own.

  Sokka and colleagues, The Journal of Rheumatology, 2009

The short answer.

Rheumatoid arthritis is an inflammatory disease, where the immune system has misread the lining of the joints. That lining swells visibly, and over years the swelling wears cartilage and bone away. It gets identified by an exam, by antibodies, and by scans, and it gets treated with disease-modifying drugs that damp the immune response down.

Fibromyalgia isn't an inflammatory disease. There's no swollen joint lining to see, no wearing away on scans, and no antibody to test for. It's a long-term widespread pain condition where pain processing itself is altered, and its best-backed treatment is exercise rather than a drug.

The overlap is real, and it causes most of the confusion. Both cause pain, stiffness, and deep tiredness, both are commoner in women, and a person can have both at once. Take somebody with controlled rheumatoid arthritis who still hurts everywhere, which is the classic case where the second diagnosis gets missed.

Side by side.

What each condition is

Rheumatoid arthritis is an autoimmune disease, where the immune system has misread the synovium, which is the lining of the joints. The lining swells and thickens, and over time the swelling wears cartilage and bone away. The damage is permanent once it happens, which is why early treatment counts so much here.

Fibromyalgia is a long-term widespread pain condition where pain processing itself is altered. There's no swelling of the joint lining, no wearing away of bone, and no autoantibody. Pain, tiredness, and sleep that doesn't refresh are the core features, and they're as real and as disabling as those of an inflammatory disease.

The difference isn't about how much somebody hurts, and it isn't about how genuine the symptoms are. It's about mechanism, and mechanism decides which treatments can possibly work. Getting it wrong sends people down a path that has no way of helping them.

What separates them in the clinic

Visible joint swelling is the single most useful finding. Rheumatoid arthritis swells the joint lining so a doctor can see and feel it, it usually shows in the small joints of the hands and feet, and it usually hits the matching joints on both sides. Fibromyalgia gives tenderness without any of that swelling.

Scans separate the two of them over time. Rheumatoid arthritis wears bone away and that shows on X-ray and ultrasound, while fibromyalgia causes no structural damage at all, however bad the pain. That's one of the harder things to explain to somebody who hurts constantly.

The antibodies point in one direction and one direction only. Anti-CCP cleared 95 percent of the people who didn't have rheumatoid arthritis, at a likelihood ratio of 12.46 for a positive result, so it argues strongly for that diagnosis. There's no matching test for fibromyalgia, because no antibody is involved to look for.

Where blood tests stop helping

Normal inflammation markers are weaker evidence than most people assume, and that's worth stating plainly because the assumption is so common. Two databases followed consecutive rheumatoid arthritis patients from 1980 to 2004, and at the first recorded measurement more than a third had one normal or negative result, meaning a normal sedimentation rate, a normal C-reactive protein, or a negative rheumatoid factor. That's a large enough share to change how a result gets read.

So normal blood work doesn't establish that an inflammatory arthritis is absent. Say somebody gets told her tests came back normal, so the pain she has must be fibromyalgia after all. She's been handed a conclusion the tests can't support on their own.

The exam and the scans count for more here than the bloods do. So that's an argument for being seen and examined by somebody, rather than an argument for repeating panels. It's the opposite of what most people expect when a diagnosis is uncertain, and it's the more useful instinct.

Why the treatments barely overlap

Rheumatoid arthritis gets treated with disease-modifying drugs, which damp down the immune response behind the joint damage. They work because there's an immune process to stop. The rush to start early comes from one fact, which is that damage to bone doesn't reverse.

Fibromyalgia has no such process to interrupt, which is why damping the immune system down doesn't help it. In the EULAR recommendations, aerobic and strengthening exercise has the top evidence rating, above cognitive behavioral therapy, above multi-part therapies, and above every drug in the set. So the best-backed treatment sits outside the pharmacy entirely.

One trial is worth knowing about, and it compared tai chi against aerobic exercise at matched intensity and length over 24 weeks. Across all the tai chi groups combined, the fibromyalgia impact questionnaire improved by 5.5 points more than with aerobic exercise, from 0.6 to 10.4. The group doing tai chi twice a week for the full 24 weeks improved by 16.2 points more, from 8.7 to 23.6, so the larger figure belongs to one schedule rather than to tai chi in general.

When somebody has both

This is the situation that causes the most frustration on both sides of the room. Take somebody with rheumatoid arthritis whose joint counts and inflammation markers look well controlled, who still hurts everywhere and is worn out. She may have developed fibromyalgia alongside her arthritis, so her arthritis looks controlled on every measure and she feels no better.

Stepping up the arthritis treatment there is unlikely to help, because the remaining symptoms aren't being driven by the inflammation the drug damps down. So spotting the second condition changes the plan. It moves from more immune damping to exercise, sleep, and pain management.

For diet, the honest answer in fibromyalgia is that nothing is established. One review covered 22 studies of 17 different things, and its authors concluded there's not enough evidence to recommend any single one of them. It did report individual signals from single small trials, so that's a field worth watching rather than acting on.

When each one fits.

• Think rheumatoid arthritis if joints are visibly swollen, if morning stiffness lasts well beyond a few minutes, and if the matching joints are affected on both sides.
• Think fibromyalgia if pain is widespread rather than centered on joints, if there's no swelling to find, and if sleep and tiredness are as bad as the pain.
• Think about both together if the arthritis measures look controlled and the person still hurts everywhere, because that's the picture most often missed.
• Don't treat normal inflammation markers as settling it, since more than a third of rheumatoid arthritis patients had a normal marker at their first measurement.
• Ask about exercise for fibromyalgia by name, because it has the top evidence rating in the EULAR recommendations and it's often the last thing offered.

Questions patients ask.