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# Pseudogout (CPPD disease)

- Lesion

Calcium pyrophosphate crystals deposit in cartilage, mostly in older people, and can set off gout-like attacks, often in the knee or wrist.

Updated Nov 12, 2026

## Key points

- Crystals: rhomboid, weakly positively birefringent (blue when parallel to the compensator axis).
- Older patients; knee most often, then wrist, shoulder, hip.
- Chondrocalcinosis: linear calcification of cartilage and menisci on X-ray.
- Associations: hyperparathyroidism, haemochromatosis, hypomagnesaemia, hypophosphatasia, hypothyroidism, previous joint injury.
- In a young patient with CPPD, look for a metabolic cause (haemochromatosis first).
- Pseudogout attacks are triggered by surgery, acute illness or trauma, like gout.

## What it is

Calcium pyrophosphate dihydrate (CPPD) deposition disease is crystal deposition in articular cartilage, menisci and other joint tissues. It is usually sporadic and age-related, sometimes hereditary (ANKH mutations), and sometimes secondary to metabolic diseases such as hyperparathyroidism, haemochromatosis, hypomagnesaemia, hypophosphatasia and hypothyroidism. It may be silent (chondrocalcinosis on X-ray), cause acute attacks (pseudogout), or produce a chronic arthritis that resembles osteoarthritis.

## Structure

- Gross: chalky white, friable deposits in cartilage.
- Micro: oval purple-blue aggregates of crystals in cartilage, menisci and synovium on H&E (better seen than urate because they survive processing).
- Acute attack: neutrophilic synovitis with phagocytosed crystals.
- Chronic: cartilage degeneration like osteoarthritis but in unusual joints (wrist, MCP, shoulder).

## Step by step

- Chondrocytes make excess inorganic pyrophosphate (aging, ANKH variants, metabolic disease).
- Pyrophosphate combines with calcium in the matrix and crystallizes.
- Crystals accumulate silently in cartilage (chondrocalcinosis).
- Released into the joint, they activate the inflammasome and draw neutrophils: acute pseudogout.
- Chronic deposits accelerate cartilage degeneration.

## Gout vs pseudogout

| Feature | Gout | Pseudogout (CPPD) |
| --- | --- | --- |
| [Crystal](https://durgical.com/en/conditions/gout/) | Monosodium urate | Calcium pyrophosphate dihydrate |
| [Shape and birefringence](https://durgical.com/en/conditions/pseudogout-of-the-knee/) | Needles, negative | Rhomboids, weakly positive |
| Typical joint | First MTP (big toe) | Knee, wrist |
| Age and sex | Middle-aged men, postmenopausal women | Older adults, both sexes |
| X-ray | Punched-out erosions with overhanging edges | Chondrocalcinosis |
| Associations | Hyperuricaemia, CKD, diuretics, alcohol | Hyperparathyroidism, haemochromatosis, low magnesium |

## Clinical notes

- An older patient with a hot knee after surgery: aspirate to look for CPPD crystals and to exclude infection.
- Treatment controls inflammation (joint aspiration, NSAIDs, colchicine, glucocorticoids); there is no drug that removes the crystals.
- Screening for calcium, magnesium, phosphate, iron studies and thyroid function finds secondary causes.

## Memory aid

Pseudogout is Positive and Pyrophosphate, in Plump rhomboids, in the knee of a grandParent.

## Test yourself

Think of the answer, then tap the question to see it.

## How do CPPD crystals look under polarized light?

Rhomboid and weakly positively birefringent.

## What is chondrocalcinosis?

Calcification of articular cartilage and menisci seen on X-ray in CPPD disease.

## Which metabolic diseases are linked to CPPD?

Hyperparathyroidism, haemochromatosis, hypomagnesaemia, hypophosphatasia and hypothyroidism.

## Which joint is most often affected by pseudogout?

The knee.

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## Connections

## Related 5

- [Pathologic calcification: dystrophic vs metastatic](https://durgical.com/en/general-pathology/pathologic-calcification-dystrophic-vs-metastatic/)
- [Gout](https://durgical.com/en/general-pathology/gout/)
- [Osteoarthritis](https://durgical.com/en/general-pathology/osteoarthritis/)
- [Hemochromatosis: hepcidin, HFE and where iron settles](https://durgical.com/en/general-pathology/hemochromatosis-hepcidin-hfe-and-where-iron-settles/)
- [Primary hyperparathyroidism](https://durgical.com/en/general-pathology/primary-hyperparathyroidism/)

## Related conditions 5

- [Pseudogout (CPPD) of the Knee](https://durgical.com/en/conditions/pseudogout-of-the-knee/)
- [Gout](https://durgical.com/en/conditions/gout/)
- [Hereditary hemochromatosis](https://durgical.com/en/conditions/hereditary-hemochromatosis/)
- [Primary hyperparathyroidism](https://durgical.com/en/conditions/primary-hyperparathyroidism/)
- [Hypomagnesaemia](https://durgical.com/en/conditions/hypomagnesaemia/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Calcium pyrophosphate arthritis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000421.htm) (MedlinePlus, US National Library of Medicine, 2025); [Gout](https://www.ncbi.nlm.nih.gov/books/NBK546606/) (StatPearls (NCBI Bookshelf), 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/pseudogout/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/pseudogout/