What's Actually Going On
Gout: long-standing high uric acid in the blood leads to needle-shaped crystals settling in and around joints. A flare is your immune system reacting to those crystals, classically at the base of the big toe, but also the knee, midfoot, ankle and wrist. Blood uric acid is largely set by your genes and kidneys, which is why diet contributes to risk but is not the whole story.
Pseudogout (CPPD): a different crystal, calcium pyrophosphate, deposits in joint cartilage and sheds into the joint, triggering the same kind of flare. It is strongly linked to ageing and often sits on top of existing wear-and-tear arthritis. It is probably the most common inflammatory arthritis in people over 60.
Why it mimics an injury: both go from normal to red-hot and agonising over a few hours. That speed, the heat and redness, and the lack of any injury that fits are what separate a crystal flare from a strain. None of those is a test. They are reasons to get the joint looked at.
How to Identify It
There is no physical examination test that diagnoses crystal arthritis, and no clinical sign that reliably rules out a joint infection. The real test is a doctor drawing a little fluid from the joint and looking at it under a microscope for crystals, plus a culture to check for infection.
Imaging is crystal-specific and only helps alongside that fluid test, not instead of it:
| Crystal | Best scan | How good |
|---|
| Gout | Dual-energy CT | catches ~89% / correctly clears ~91% |
| Gout | Ultrasound (double-contour sign) | catches ~70% / correctly clears ~95% |
| Pseudogout | Ultrasound | catches ~85% / X-ray only ~47% |
What it is not: the most important thing to separate a crystal flare from is a joint infection, which can look identical and can even happen at the same time. That is why a hot joint gets its fluid drawn and cultured, and why a positive crystal result never, by itself, clears the joint.
The Debate
"Stop your gout tablet during an attack"
Older common advice was to pause uric-acid-lowering medication during a flare. A randomised trial (starting febuxostat during a flare) found the attack lasted essentially the same, about 6 days either way, and pooled analyses agree.
Follow the trial evidence: keep taking it. Stopping it does not help.
"A crystal result rules out infection"
A large review of the acute hot joint found no single blood or joint-fluid test that could safely replace looking at the fluid under a microscope and culturing it, and crystals and infection can coexist.
Aspirate and culture the joint regardless of crystals if the picture could be septic.
Honest Limitations
The scan accuracy comes from specialists, not walk-in clinics
The good dual-energy CT and ultrasound numbers were produced by expert operators against confirmed cases. A community clinic does not have that kit on hand, and ultrasound for pseudogout is operator-dependent. The figures justify referring for a proper diagnosis; they do not put a test in a therapist's hands.
Pseudogout treatment is borrowed, not proven
Almost everything done for a pseudogout flare is copied from gout. A review found only three small randomised trials in pseudogout, and one of them was negative. Confidence in "what to do for pseudogout" should stay modest.
The infection literature is old and cannot give a clean rule-out
The best reviews still conclude that no test beats an experienced clinician plus drawing fluid from the joint. When the evidence cannot rule infection out, the safe move is to refer.
The Nuance
Crystal disease is not always where you'd look for it. In older adults it can show up as sudden severe neck pain with a fever and raised inflammation markers, caused by calcium crystals around the top of the spine. This is called crowned dens syndrome, and in a review of nearly 200 cases it was mistaken for meningitis about one time in five. A CT scan is what catches it.
Pseudogout can also flag a hidden problem. A first, early, or unusually severe case can be a signal of an underlying condition such as iron overload, an overactive parathyroid gland, or low magnesium, which is worth a check with your doctor.
And because a single gout or pseudogout flare settles on its own within a week or two even without treatment, any "cure" someone swears by after their attack faded is almost certainly taking credit for time passing.
