A 78-year-old man who resides in a skilled nursing facility is evaluated for acute-onset s… — USMLE Step 2 CK

A $78$ -year-old man who resides in a skilled nursing facility is evaluated for acute-onset severe pain and swelling in his right knee that began $24$ hours ago. He has a history of hypertension, diet-controlled type 2 diabetes mellitus, and advanced chronic kidney disease with a baseline serum creatinine of $2.6 \text{ mg/dL}$ . Vital signs are within normal limits except for a temperature of $37.7^\circ\text{C}$ ( $99.9^\circ\text{F}$ ). Physical examination reveals a warm, erythematous, and swollen right knee with a moderate effusion. Range of motion is severely limited by pain. Arthrocentesis yields $4 \text{ mL}$ of cloudy, yellow synovial fluid. Analysis shows a leukocyte count of $32,000/\mu\text{L}$ with $90\%$ neutrophils. Polarized light microscopy demonstrates rhomboid-shaped crystals with weak positive birefringence. Gram stain reveals no organisms. Which of the following is the most appropriate next step in management?

Intra-articular triamcinolone injectionAnswer
B
Empiric intravenous vancomycin
C
Oral naproxen
D
Oral allopurinol
E
Intravenous furosemide

Answer

The correct answer is intra-articular triamcinolone injection.

This patient's presentation of an acutely painful, swollen joint with synovial fluid demonstrating rhomboid-shaped, positively birefringent crystals is diagnostic of an acute flare of calcium pyrophosphate deposition (CPPD) disease, commonly known as pseudogout. The synovial leukocyte count of

32,000/\mu\text{L}

is consistent with an inflammatory arthritis. First-line treatments for acute CPPD flares typically include NSAIDs, oral colchicine, or intra-articular glucocorticoids. However, this patient has advanced chronic kidney disease (baseline creatinine

2.6 \text{ mg/dL}

). In this setting, NSAIDs are contraindicated due to the risk of precipitating acute renal failure, and colchicine is highly discouraged due to the risk of severe neuromyotoxicity and bone marrow suppression. Therefore, an intra-articular injection of a glucocorticoid (like triamcinolone) is the safest and most appropriate next step, providing targeted relief without systemic or renal toxicity.

Step-by-Step Solution

Interpret the synovial fluid analysis.

The fluid shows

32,000/\mu\text{L}

leukocytes and rhomboid-shaped, positively birefringent crystals.

This confirms an acute flare of calcium pyrophosphate deposition (CPPD) disease (pseudogout) rather than septic arthritis.

Evaluate the patient's comorbidities for contraindications to standard therapies.

The patient has advanced chronic kidney disease (creatinine

2.6 \text{ mg/dL}

Standard first-line agents for pseudogout (NSAIDs and colchicine) are contraindicated or carry high toxicity risk in advanced renal impairment.

Select the safest and most effective targeted therapy.

Intra-articular glucocorticoid injection (e.g., triamcinolone) is chosen.

It provides excellent local anti-inflammatory effect while minimizing systemic absorption and avoiding renal toxicity.

Key Concept

Management of acute calcium pyrophosphate deposition (CPPD) disease flares involves avoiding NSAIDs and colchicine in patients with advanced chronic kidney disease, favoring intra-articular glucocorticoids.

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