From the Guidelines
Pseudogout should be diagnosed based on a combination of clinical presentation, imaging findings, and synovial fluid analysis, with a focus on identifying calcium pyrophosphate crystals under polarized light microscopy, as recommended by the 2023 EULAR guidelines 1. Pseudogout presents as acute, painful joint inflammation caused by calcium pyrophosphate crystal deposition. Patients typically experience sudden onset of severe joint pain, swelling, warmth, and limited range of motion, most commonly affecting the knee, wrist, ankle, or shoulder. Unlike gout, pseudogout affects older adults (usually over 60) and may occur following surgery, trauma, or severe medical illness.
Key Diagnostic Findings
- Joint aspiration with synovial fluid analysis showing weakly positive birefringent rhomboid-shaped crystals under polarized light microscopy
- Chondrocalcinosis (calcification of cartilage) on X-rays
- Elevated inflammatory markers like ESR and CRP
- Laboratory tests should include serum calcium, phosphate, magnesium, alkaline phosphatase, and thyroid function to identify underlying metabolic disorders that may contribute to calcium pyrophosphate deposition
Differential Diagnosis
- Gout
- Septic arthritis
- Rheumatoid arthritis
- Osteoarthritis Pseudogout attacks can be distinguished from gout by crystal type, joint distribution (pseudogout rarely affects the first MTP joint), and lack of response to typical gout medications like allopurinol, as noted in the EULAR recommendations for calcium pyrophosphate deposition management 1. The 2023 EULAR guidelines on imaging in diagnosis and management of crystal-induced arthropathies also recommend the use of conventional radiography and ultrasound in the diagnostic assessment of CPPD 1. Prompt diagnosis is important as treatment approaches differ from other inflammatory arthritides.
From the Research
Pseudogout Presentation
- Pseudogout, also known as calcium pyrophosphate dihydrate deposition disease (CPPD), is a metabolic arthropathy characterized by the deposition of calcium pyrophosphate crystals in articular cartilage and periarticular tissues 2.
- The disease manifests in three clinical forms: asymptomatic, acute, and chronic 2.
- Acute CPP crystal arthritis is characterized by sudden onset of pain, swelling, and tenderness with overlying erythema, usually in a large joint, such as the knee, wrist, shoulder, or hip 3.
- Chronic inflammatory arthritis is characterized by joint swelling, morning stiffness, pain, and high ESR and CRP 3.
Diagnosis of Pseudogout
- Diagnosis is made on the basis of X-ray or ultrasound examination, but definitive confirmation requires demonstration of calcium pyrophosphate dihydrate crystals in the synovial fluid 2.
- Non-polarized light microscopy should be used initially to screen for CPPD crystals based on their characteristic morphology, and compensated polarized light microscopy is recommended for definitive identification 3.
- Fine needle aspiration cytology (FNAC) can also play a pivotal role in accurately diagnosing the disease, especially when other modalities like radiology and histopathology fail to do so 4.
- Evaluation of history and clinical features, conventional radiology, and synovial fluid examination are also important for diagnosis 3.
Clinical Forms and Associations
- CPPD disease can present in four different clinical forms: asymptomatic CPPD, osteoarthritis (OA) with CPPD, acute CPP crystal arthritis, and chronic CPP inflammatory crystal arthritis 3.
- The relationship between OA and CPPD is still unclear, with some uncertainty as to whether CPPD crystals are directly involved in the pathogenesis of OA or are a result of joint degeneration 3.
- CPPD disease is often indistinguishable from gout and is therefore commonly referred to as "pseudogout" 5.