Pseudogout (CPPD) and gout

What CPPD is

CPPD stands for calcium pyrophosphate deposition. It used to be called pseudogout, and many people still use that name. MedlinePlus describes it as a joint disease that can cause attacks of arthritis. Like gout, crystals form in the joints. Unlike gout, the crystals are not made of uric acid.

MedlinePlus notes that CPPD mainly affects older adults, and that in many people the deposits cause no symptoms at all. The Arthritis Foundation notes that gout symptoms can be confused with CPPD.

Two kinds of crystal

In gout, the crystals are made from urate (uric acid). In CPPD, they are made from calcium pyrophosphate. Both can set off a hot, painful, swollen joint. A joint on its own does not tell you which crystal is behind it.

How they are told apart

MedlinePlus says carefully testing joint fluid for crystals can help a clinician make the diagnosis. A clinician uses a needle to take a sample of fluid from the joint, and the sample is examined under a microscope. NIAMS describes the same kind of test for gout, looking for urate crystals. X-rays and other imaging can also help. A blood urate test alone does not settle it.

Infection can look like either one at the start. That is part of why a new hot joint, especially with fever, needs a clinician rather than a guess. More on the tests is on How gout is diagnosed.

Where each tends to show up

MedlinePlus says CPPD attacks happen most often in the knees, wrists, ankles, and shoulders, and that, in contrast to gout, the joint at the base of the big toe is not often affected. NIAMS says gout flares often begin in the big toe or a lower limb. These are tendencies, not rules. Either condition can turn up in other joints.

Illustration of the bones of a bent knee from the side with the knee joint highlighted — CPPD (pseudogout)
Highlighted: the knee joint, seen from the side. The knee is one of the places MedlinePlus names for CPPD attacks.

Illustration of the bones of the foot from above with the big toe joint highlighted — Gout
Highlighted: the big toe joint (first MTP joint), seen from above. The big toe is the classic place a gout flare starts.

Side by side

Gout and CPPD, in plain words. Not a way to self-diagnose.
Gout	CPPD (pseudogout)
Crystals made from urate (uric acid).	Crystals made from calcium pyrophosphate.
Often starts in the big toe or another lower-limb joint (NIAMS).	Most often the knees, wrists, ankles, and shoulders; the big toe less often (MedlinePlus).
Joint fluid under a microscope shows urate crystals.	Joint fluid under a microscope shows calcium pyrophosphate crystals.
Long-term plan can include urate-lowering medicine, decided with a clinician.	MedlinePlus notes there is no treatment to remove the CPPD crystals; care focuses on the attacks and the joint.

Why it matters

The two conditions can need different plans. Urate-lowering medicine such as allopurinol is aimed at urate. It is a gout plan, not a CPPD plan. Flare medicines can overlap; MedlinePlus lists steroids, NSAIDs, and colchicine among the options for CPPD attacks. Which one, if any, is chosen with you, not by this page.

If you were told you have gout but your flares do not fit the usual pattern, it is a fair question to ask whether crystals were ever seen. Questions like that are on Questions to ask. Other joint problems that can sit beside gout are on Other conditions.

Clinical claims on this page follow the sources.