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Pseudogout is a crystal-induced arthropathy caused by deposition of calcium pyrophosphate dihydrate (CPPD) crystals within joints, fibrocartilage, and hyaline cartilage.

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The term “pseudogout” refers to the acute arthritis clinically resembling gout, while the broader entity is called CPPD deposition disease (CPPD arthropathy).

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Etiopathogenesis

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Crystal formation: Due to imbalance in inorganic pyrophosphate metabolism → deposition of CPPD crystals in cartilage.

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Risk factors / associations:

Clinical Features

| Acute pseudogout attack | • Monoarticular arthritis, most commonly affecting the knee; also wrist, shoulder, ankle. • Sudden onset of pain, swelling, warmth, and decreased mobility. • Attacks may be precipitated by surgery, trauma, or intercurrent illness. | | --- | --- | | Chronic CPPD arthropathy | • Mimics osteoarthritis or rheumatoid arthritis with progressive joint degeneration. • Involves atypical joints such as radiocarpal, MCP, or shoulder. | | Asymptomatic chondrocalcinosis | Radiological finding without clinical arthritis. |

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Radiology

Modality Imaging features
XR/CT Chondrocalcinosis – linear or punctate calcification within hyaline or fibrocartilage.
• Knee: menisci and articular cartilage.
• Wrist: triangular fibrocartilage complex (TFCC).
• Pubic symphysis, acetabular labrum, glenohumeral joint may also be involved.
US Hyperechoic linear bands within cartilage, parallel to subchondral bone.

![Clinical, radiological and microscopic aspects of gout and calcium pyrophosphate (CPP) crystal deposition. (A) Chronic tophaceous gout (1) with severe joint destructions at radiograph (2) in a male patient with long-standing polyarticular gout. Synovial fluid analysis collected from the V metacarpophalangeal joint showed an aggregate of needle-shape monosodium urate crystals (3). (B) CPP crystal deposition in the knee of a patient with recurrent pseudogout attacks (1). CPP crystals (arrows) observed in synovial fluid under compensated polarized light (2). (C) Axial CT image of a male patient's cervical spine at C1-C2, illustrating the “crowning” of the dens. Arrow represents CPP deposition. Original figures obtained and reproduced with patients' written informed consent to publication.

Oliviero F, Bindoli S, Scanu A, et al. Autoinflammatory mechanisms in Crystal-Induced arthritis. Frontiers in Medicine. 2020;7. doi:10.3389/fmed.2020.00166](attachment:8f1f22c1-e53d-4093-b905-683933c9a11a:image.png)

Clinical, radiological and microscopic aspects of gout and calcium pyrophosphate (CPP) crystal deposition. (A) Chronic tophaceous gout (1) with severe joint destructions at radiograph (2) in a male patient with long-standing polyarticular gout. Synovial fluid analysis collected from the V metacarpophalangeal joint showed an aggregate of needle-shape monosodium urate crystals (3). (B) CPP crystal deposition in the knee of a patient with recurrent pseudogout attacks (1). CPP crystals (arrows) observed in synovial fluid under compensated polarized light (2). (C) Axial CT image of a male patient's cervical spine at C1-C2, illustrating the “crowning” of the dens. Arrow represents CPP deposition. Original figures obtained and reproduced with patients' written informed consent to publication.

Oliviero F, Bindoli S, Scanu A, et al. Autoinflammatory mechanisms in Crystal-Induced arthritis. Frontiers in Medicine. 2020;7. doi:10.3389/fmed.2020.00166