Msk Dermatology · Year 2 · from Msk Dermatology

Case 3: Calcium Pyrophosphate Deposition Disease (Pseudogout)

Patient Presentation

Demographics: 75-year-old woman

Chief Complaint: "My right knee suddenly became swollen and painful after my hip surgery last week."

History of Present Illness: The patient underwent right total hip arthroplasty 8 days ago for osteoarthritis. She was recovering well until 2 days ago when she developed acute pain and swelling in her right knee without any trauma. The knee became increasingly swollen, warm, and painful, making it difficult to participate in physical therapy. She had a similar episode affecting her left knee 3 years ago that was diagnosed as "pseudogout."

Past Medical History:

• Osteoarthritis (hips, knees)
• Hypothyroidism
• Type 2 diabetes mellitus
• Prior episode of "pseudogout" left knee 3 years ago

Medications:

• Levothyroxine 75 mcg daily
• Metformin 1000 mg twice daily
• Enoxaparin 40 mg subcutaneously daily (DVT prophylaxis post-surgery)
• Oxycodone/acetaminophen 5/325 mg PRN pain

Surgical History:

• Right total hip arthroplasty 8 days ago

Physical Examination

• Vital Signs: BP 138/82 mmHg, HR 84 bpm, Temp 37.6C
• General: Elderly woman, uncomfortable but not toxic
• Right Knee:
• Large tense effusion
• Warmth and erythema
• Moderate tenderness
• Limited range of motion due to pain and swelling
• Right Hip: Surgical incision healing well, no signs of infection
• Left Knee: Mild crepitus, no effusion

Workup and Results

Laboratory Studies:

Synovial Fluid Analysis:

Imaging:

• Knee radiographs:
• Chondrocalcinosis: linear calcification in menisci bilaterally
• Moderate degenerative changes
• Large effusion

Diagnosis

Acute Calcium Pyrophosphate Crystal Arthritis (Pseudogout)

Diagnostic Features:

• CPP crystals identified on polarized microscopy (rhomboid, weakly positive birefringent - blue when parallel to compensator)
• Chondrocalcinosis on radiographs
• Post-surgical trigger (acute illness/surgery commonly precipitates CPPD flares)
• Prior documented episode
• Elderly patient (CPPD prevalence increases with age)

Secondary Causes Excluded:

• Primary hyperparathyroidism: normal calcium and PTH
• Hemochromatosis: normal ferritin
• Hypomagnesemia: normal magnesium
• Hypothyroidism: controlled on replacement

Treatment Plan

Acute Attack Management:

1. Intra-articular corticosteroid injection: Triamcinolone 40 mg injected after aspiration

• Preferred given recent surgery, diabetes, and anticoagulation limiting systemic options

1. Ice, rest, elevation
2. Physical therapy: May resume once acute inflammation subsides

Systemic Options if Needed:

• Low-dose colchicine (0.6 mg BID) if flare recurs
• Short course oral prednisone if multiple joints involved

Prophylaxis (if recurrent):

• Consider low-dose colchicine 0.6 mg daily for frequent flares

Follow-up:

• Continue DVT prophylaxis as planned
• Resume physical therapy when tolerated
• No disease-modifying therapy exists for CPPD (unlike gout)

Teaching Points

1. CPPD triggers: Acute illness, surgery, and trauma commonly precipitate pseudogout attacks; post-operative flares are well-recognized
2. CPP crystal identification: Rhomboid or rod-shaped, weakly positive birefringent (blue when parallel to compensator) - opposite to MSU crystals
3. Chondrocalcinosis: Radiographic calcification of cartilage (menisci, triangular fibrocartilage, pubic symphysis) supports diagnosis
4. Secondary causes: Check calcium/PTH, ferritin, magnesium in younger patients or those with severe disease; less necessary in typical elderly presentation
5. No disease-modifying therapy: Unlike gout, no treatment dissolves CPP crystals or prevents deposition; management is symptomatic
6. Knee predominance: The knee is the most commonly affected joint in CPPD (unlike first MTP in gout)

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