Pseudogout Crystal Morphology and Clinical Characteristics
Pseudogout crystals appear as rhomboid-shaped or rod-like calcium pyrophosphate dihydrate (CPPD) crystals that show weak positive birefringence under polarized light microscopy, distinguishing them from the needle-shaped, negatively birefringent monosodium urate crystals seen in gout. 1, 2
Crystal Characteristics
The definitive identification of pseudogout requires synovial fluid analysis demonstrating:
- Rhomboid or rectangular-shaped crystals that are typically shorter and blunter than gout crystals 1
- Weak positive birefringence under compensated polarized light microscopy (appearing blue when parallel to the compensator axis, opposite to gout crystals) 2
- Calcium pyrophosphate dihydrate composition confirmed through crystal analysis 1, 3
Clinical Presentation in Older Adults
Pseudogout predominantly affects elderly patients and presents with distinct patterns:
Acute Attacks
- Sudden onset of severe joint pain, swelling, and erythema similar to gout but typically affecting larger joints 3
- Most commonly involves knees, wrists, shoulders, and hips rather than the first metatarsophalangeal joint typical of gout 4, 5
- Can present as monoarticular disease (single joint) or polyarticular involvement 5, 3
- May mimic septic arthritis or other inflammatory conditions, requiring joint aspiration for definitive diagnosis 4
Radiographic Features
- Chondrocalcinosis: linear or stippled calcification of cartilage visible on plain radiographs 2
- In atypical presentations, may show diffuse calcification patterns rather than the classic linear appearance 2
- Can present as tumor-like calcified masses around joints, mimicking neoplastic lesions 1
Management Strategies
Acute Attack Treatment
The treatment approach mirrors gout management but must account for the elderly population's comorbidities:
- NSAIDs, corticosteroids, or colchicine are first-line options for acute attacks 3
- Low-dose colchicine is preferred when using this agent to minimize toxicity in older adults with renal impairment 3
- Intra-articular corticosteroid injection can be effective for monoarticular disease 3
- For severe, refractory cases, interleukin-1 inhibitors (such as anakinra) provide rapid symptom relief by targeting the NALP-3 inflammasome pathway 4, 3
Prophylactic Management
- Colchicine prophylaxis may reduce frequency of recurrent attacks by modulating the NALP-3 inflammasome of the innate immune system 3
- Unlike gout, no agents currently exist to decrease CPPD crystal load or reverse crystal deposition 3
Special Considerations in Older Adults
- Multiple medical comorbidities (chronic kidney disease, cardiovascular disease, diabetes) require careful medication selection 3
- Chronic renal failure patients have higher incidence of pseudogout (15.8% in those over age 60) and may present with atypical features 2
- Joint aspiration with polarized light microscopy remains essential to differentiate from septic arthritis, particularly in immunocompromised or post-surgical patients 4
Critical Diagnostic Pitfalls
- Pseudogout can mimic infection, presenting with fever, elevated inflammatory markers, and radiographic findings suggesting discitis or epidural abscess 4
- Tumor-like presentations with large calcified masses require histopathological examination to exclude neoplasia 1
- Monoarticular hip involvement is rare but should be considered in unexplained hip pain, potentially requiring arthroscopy for diagnosis 5
- Always perform synovial fluid analysis with polarized microscopy when clinical judgment indicates diagnostic testing is necessary, as recommended for crystal arthropathy diagnosis 6