An 80-year-old male resident of an assisted living facility is brought to the urgent care … — USMLE Step 2 CK

An 80-year-old male resident of an assisted living facility is brought to the urgent care clinic complaining of excruciating right knee pain that started abruptly 24 hours ago. His medical history is significant for generalized osteoarthritis and well-controlled heart failure. His current temperature is $37.8^\circ C$ ( $100.0^\circ F$ ), blood pressure is $135/82$ mmHg, and heart rate is $88$ /min. Examination of the right knee demonstrates prominent swelling, marked warmth, and erythema, with passive range of motion severely limited by pain. Synovial fluid aspirated from the joint reveals a leukocyte count of $32,000/\mu L$ (88% segmented neutrophils). Polarized light microscopy identifies numerous rhomboid-shaped crystals exhibiting weak positive birefringence. Gram stain is negative for bacteria. Plain films of the affected joint exhibit linear calcification of the meniscal cartilage. Which of the following is the most appropriate next step in management?

Intra-articular injection of a glucocorticoidAnswer
B
Initiation of intravenous vancomycin and ceftriaxone
C
Administration of intravenous furosemide
D
Measurement of serum thyroid-stimulating hormone levels
E
Urgent orthopedic consultation for arthroscopic joint lavage

Answer

Intra-articular injection of a glucocorticoid

The patient's presentation is classic for an acute flare of calcium pyrophosphate deposition (CPPD) disease, or pseudogout. The pathognomonic findings are rhomboid-shaped, weakly positively birefringent crystals on synovial fluid analysis and chondrocalcinosis on plain radiography. For a patient with a monoarticular flare—especially an elderly patient with significant comorbidities like heart failure, where NSAIDs are relatively contraindicated—intra-articular glucocorticoids are the safest and most effective targeted first-line therapy.

Step-by-Step Solution

Analyze the synovial fluid analysis and microscopy findings.

The fluid shows

32,000/\mu L

leukocytes (inflammatory but non-purulent) and rhomboid-shaped, weakly positively birefringent crystals.

Identifying the specific crystal type is required to differentiate between gout (needle-shaped, negatively birefringent) and pseudogout (rhomboid-shaped, positively birefringent).

Identify the primary diagnosis based on combined clinical and laboratory clues.

The diagnosis is an acute flare of Calcium Pyrophosphate Deposition (CPPD) disease, commonly known as pseudogout, supported by the imaging finding of chondrocalcinosis.

Accurate diagnosis dictates specific pharmacotherapy and rules out life-threatening conditions like septic arthritis.

Determine the optimal acute management for this specific patient.

Intra-articular glucocorticoids are selected over systemic NSAIDs or colchicine.

The patient is elderly with heart failure. NSAIDs can exacerbate heart failure and cause renal impairment. Localized therapy with an intra-articular injection safely and rapidly treats a monoarticular flare.

Key Concept

Diagnosis and acute management of calcium pyrophosphate deposition (CPPD) disease (pseudogout).

Estimated Time:1m 0s

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