A 55-year-old man presents with a 2-day history of mono-articular joint pain. He is otherwise healthy and denies fever, chills, or recent trauma. His medical history is notable for a kidney stone 6 months ago. He underwent a dental procedure to extract an infected wisdom tooth 3 weeks ago. The patient does not take any medications. He is a non-smoker and does not drink alcohol or use recreational drugs. His family history is significant for osteoarthritis in his father who is 78. His temperature is 98.6°F (37°C), blood pressure is 133/84 mmHg, pulse is 84/min, and respirations are 15/min. His body mass index is 27 kg/m^2. Physical examination shows a swollen and tender joint with overlying erythema. Diagnostic arthrocentesis is performed and shows a leukocyte count of 30,000/mm^3 with 85% neutrophils. Polarized microscopy of the synovial fluid is shown in Figure A. Which of the following would most likely be found on this patient’s radiograph?
Tophi
Heberden nodes
Juxta-articular osteoporosis
Chondrocalcinosis
Chondrocalcinosis
This patient is presenting with a joint aspiration positive for calcium pyrophosphate dehydrate crystals, suggesting a diagnosis of pseudogout, which may show chondrocalcinosis on radiography.

Pseudogout presents classically with mono- or oligo-articular arthritis that most often affects the knee and proximal joints of elderly patients (> 60 years of age). The disease can be associated with hyperparathyroidism, Gitelman syndrome, familial hypocalciuric hypercalcemia, and hemochromatosis. The patient will have a leukocyte count < 50,000/mm^3 on joint aspiration and positively birefringent, rhomboid-shaped cells on microscopy, which represent calcium pyrophosphate dehydrate (CPPD) crystals. On radiography, chondrocalcinosis can be found, which is the calcification of adjacent cartilaginous structures. Treatment is with indomethacin.

Sidari and Hill review the evidence regarding the diagnosis and treatment of gout and pseudogout. They discuss how diagnosis can be made with fluid microscopy. They recommend treatment with non-steroidal anti-inflammatory drugs.

Figure/Illustration A is polarized microscopy of joint fluid showing rhomboid-shaped crystals that are positively birefringent (red circles). These represent calcium pyrophosphate dehydrate crystals seen in pseudogout.

Incorrect Answers:
Answer A: Boutonniere deformity is characterized by proximal interphalangeal (PIP) joint flexion and distal interphalangeal (DIP) joint extension and is a common hand deformity of rheumatoid arthritis. Rheumatoid arthritis is characterized by insidious onset of morning stiffness and pain that usually affects symmetric PIP and metacarpophalangeal (MCP) joints first. On joint aspiration, leukocyte count ranges from 5,000-50,000/mm^3, but rheumatoid arthritis would not explain the CPPD crystals. Treatment may include methotrexate.

Answer C: Heberden nodes are bony protuberances in the DIP joints, which are characteristic of osteoarthritis. Osteoarthritis presents with insidious onset of joint pain that worsens with activity and weight-bearing. On joint aspiration, the leukocyte count is < 2,000/mm^3.

Answer D: Juxta-articular osteoporosis is decreased bone density of the bone surrounding the joint space. It is a nonspecific sign that can be seen with many inflammatory joint diseases such as rheumatoid arthritis or septic arthritis. Septic arthritis presents with mono-articular joint pain, erythema, and swelling. Joint aspiration will show a leukocyte count > 50,000/mm^3 and Gram stain may be positive.

Answer E: Tophi are deposits of urate crystals in the soft tissue, which are nearly pathognomonic for gout. Gout presents as acute, mono-articular joint pain with physical examination showing a red, inflamed joint (usually the first metatarsophalangeal, knee, or ankle joint). Needle-shaped, negatively birefringent urate crystals are seen in the joint fluid aspirate. Prevention may include allopurinol.

Bullet Summary:
Pseudogout is associated with positively birefringent, rhomboid-shaped crystals and chondrocalcinosis.