Pseudogout and CPPD Disease

Pseudogout is the acute, gout-like inflammatory arthritis caused by calcium pyrophosphate dihydrate crystals, and it is one presentation of the broader calcium pyrophosphate deposition disease. The shared feature is deposition of calcium pyrophosphate crystals in cartilage and joint tissue, which can be silent, cause acute flares resembling gout, or produce a chronic arthritis.

Definition

Pseudogout is an acute inflammatory arthritis caused by calcium pyrophosphate dihydrate crystals, and is one clinical form of calcium pyrophosphate deposition disease, the family of conditions arising from deposition of calcium pyrophosphate crystals in articular cartilage and other joint tissues.

Scope

This entry introduces pseudogout and calcium pyrophosphate deposition (CPPD) disease as clinical phenomena: the crystals involved, the spectrum from asymptomatic chondrocalcinosis to acute pseudogout to chronic CPP arthritis, how the condition is recognised and distinguished from gout, and its epidemiology in older adults. The detailed disease entry is held under the companion calcium-pyrophosphate-deposition node; this topic emphasises the acute pseudogout presentation and terminology. It is reference material and not clinical guidance.

Key concepts

• Calcium pyrophosphate dihydrate crystals
• Chondrocalcinosis (cartilage calcification on imaging)
• Acute CPP crystal arthritis (pseudogout)
• Asymptomatic CPPD versus symptomatic disease
• Chronic CPP crystal inflammatory arthritis
• Positively birefringent rhomboid crystals on polarised microscopy
• Association with ageing and osteoarthritis
• Metabolic associations (e.g. haemochromatosis, hyperparathyroidism)

Mechanisms

Calcium pyrophosphate deposition disease arises when calcium pyrophosphate dihydrate crystals form in cartilage, reflecting dysregulated inorganic pyrophosphate metabolism within chondrocytes and their matrix. The deposited crystals may remain clinically silent (seen only as chondrocalcinosis on imaging) or shed into the joint space, where they are recognised by innate immune cells and provoke an acute inflammatory flare — pseudogout — that clinically resembles gout. Repeated or persistent crystal-driven inflammation can produce a chronic arthritis. Identification rests on detecting calcium pyrophosphate crystals in synovial fluid, classically rhomboid and weakly positively birefringent under polarised light, which distinguishes them from the needle-shaped, negatively birefringent urate crystals of gout.

Clinical relevance

Pseudogout is an important cause of acute monoarthritis or oligoarthritis in older adults and a key entity to differentiate from gout and from septic arthritis; chondrocalcinosis is also a common incidental imaging finding whose significance has to be interpreted in context. This entry explains how the condition is conceptualised and recognised; it is educational and does not provide individual diagnostic or treatment advice.

Epidemiology

Calcium pyrophosphate deposition is strongly associated with ageing: radiographic chondrocalcinosis becomes increasingly common in later decades of life, and CPPD is a frequent cause of inflammatory arthritis in older people. It is associated with osteoarthritis and, in some cases, with metabolic conditions such as haemochromatosis and primary hyperparathyroidism, which are relevant when the disease appears at a younger age or in an atypical pattern.

History

The condition was delineated in the early 1960s when calcium pyrophosphate crystals were identified in the synovial fluid of patients with acute attacks clinically resembling gout, leading to the term "pseudogout" and the recognition of a distinct calcium-crystal arthropathy separate from urate gout. Subsequent work clarified the spectrum from asymptomatic chondrocalcinosis to chronic arthritis, and European recommendations later standardised terminology, naming calcium pyrophosphate deposition (CPPD) disease and its clinical forms.

Debates

How should the condition be named and subclassified?

Terminology has shifted from older labels toward a standardised scheme distinguishing chondrocalcinosis, acute CPP crystal arthritis (pseudogout) and chronic CPP crystal inflammatory arthritis, and the relationship of these forms to osteoarthritis remains an area of refinement.

Seminal works

• mccarty-1962
• rosenthal-ryan-2016
• zhang-2011-cppd-1

Frequently asked questions

How is pseudogout different from gout?

Both are crystal arthritides with similar acute presentations, but pseudogout is caused by calcium pyrophosphate dihydrate crystals (rhomboid, weakly positively birefringent), whereas gout is caused by monosodium urate crystals (needle-shaped, strongly negatively birefringent).

Does chondrocalcinosis always cause symptoms?

No. Chondrocalcinosis — calcium pyrophosphate crystal deposition visible in cartilage on imaging — is frequently asymptomatic, especially in older adults, and only some people develop acute pseudogout or chronic arthritis.