A 75-year-old man is admitted to the hospital with fever, chills, productive cough, and difficulty breathing. His initial evaluation shows leukocytosis and right lower lobe consolidation. Appropriate antibiotic therapy is started and the patient has gradual improvement. On the third hospital day, he awakens with sudden pain and swelling of the right knee. The patient has a history of chronic knee pain that he attributes to standing "all day, all my life" as an assembly line worker, but he has never had pain of this intensity. Medical history is notable for hypertension, type 2 diabetes mellitus, and gastroesophageal reflux disease.
Temperature is 37 C (98.6 F) , blood pressure is 150/90 mm Hg, pulse is 84/min, and respirations are 14/min. On examination, the patient appears uncomfortable. The right knee joint is swollen, red, warm, and tender, and he is unable to bend the knee due to pain.
Blood cell counts and serum chemistry studies are within normal limits. Blood culture performed at the time of admission shows no growth. Synovial fluid analysis reveals 20,600/mm³ leukocytes with 90% neutrophils; Gram stain is negative and no crystals are visualized. Synovial fluid culture and repeat blood cultures are sent. Right knee x-ray is shown in the exhibit.
Which of the following is the most likely cause of this patient's knee pain?

Question

A 75-year-old man is admitted to the hospital with fever, chills, productive cough, and difficulty breathing. His initial evaluation shows leukocytosis and right lower lobe consolidation. Appropriate antibiotic therapy is started and the patient has gradual improvement. On the third hospital day, he awakens with sudden pain and swelling of the right knee. The patient has a history of chronic knee pain that he attributes to standing "all day, all my life" as an assembly line worker, but he has never had pain of this intensity. Medical history is notable for hypertension, type 2 diabetes mellitus, and gastroesophageal reflux disease.
Temperature is 37 C (98.6 F) , blood pressure is 150/90 mm Hg, pulse is 84/min, and respirations are 14/min. On examination, the patient appears uncomfortable. The right knee joint is swollen, red, warm, and tender, and he is unable to bend the knee due to pain.
Blood cell counts and serum chemistry studies are within normal limits. Blood culture performed at the time of admission shows no growth. Synovial fluid analysis reveals 20,600/mm³ leukocytes with 90% neutrophils; Gram stain is negative and no crystals are visualized. Synovial fluid culture and repeat blood cultures are sent. Right knee x-ray is shown in the exhibit.

Which of the following is the most likely cause of this patient's knee pain?

Quizplus · Accepted Answer

11ec193a_991c_0277_853d_7537cc41b925_MD0002_00 This patient's x-ray reveals chondrocalcinosis (calcium deposits in cartilage) in the joint space between the femur and tibia. Chondrocalcinosis is common in asymptomatic elderly individuals, but in acute inflammatory arthritis it suggests calcium pyrophosphate dihydrate (CPPD) deposition disease (pseudogout). Pseudogout most commonly affects the knee and can be accompanied by systemic symptoms (eg, fever). It often resembles acute gout, and both gout and pseudogout can be triggered by acute illness. chondrocalcinosis Synovial fluid analysis with polarized light microscopy is recommended for diagnosis and may be needed to distinguish between gout and pseudogout (CPPD crystals are rhomboid and have weak positive birefringence; uric acid crystals are needle-shaped and have negative birefringence). However, CPPD crystals are small, often scarce, and crystal microscopy alone has low sensitivity. Patients with acute gout or pseudogout can occasionally have synovial fluid white blood cell (WBC) counts of 50,000-100,000/mm³ (pseudo-septic arthritis), but counts of 15,000-30,000/mm³ (as in this patient) are more characteristic. Treatment options include nonsteroidal anti-inflammatory drugs, intra-articular glucocorticoids, or colchicine. ³ ³ (Choice A) Charcot arthropathy (diabetic neuropathic arthropathy) is most common in patients with long-standing diabetic peripheral neuropathy. It presents with acute warmth and swelling in the foot or ankle but relatively little pain. This patient's severe pain and chondrocalcinosis are more consistent with pseudogout. (Choice C) Although osteoarthritis can occasionally cause swelling and redness, it typically shows <2,000 WBCs in the synovial fluid and symptoms are usually less acute than in this patient. (Choice D) Reactive arthritis usually presents after an infection (usually enteric or urethritis) with asymmetric oligoarthritis, inflammatory synovial fluid findings, and extraarticular symptoms (eg, conjunctivitis, genital lesions). This patient's lack of extraarticular symptoms makes reactive arthritis less likely. (Choice E) Synovial fluid findings to suggest septic arthritis include >100,000 WBCs/mm³ (80%-90% neutrophils) and visible organisms on Gram stain. This patient's overall clinical improvement on antibiotics, negative blood cultures, and synovial fluid findings (WBCs <50,000/mm³, 70% neutrophils) make pseudogout more likely. ³ ³ Educational objective: Acute crystal arthritis, such as gout or pseudogout, often occurs in patients hospitalized with for acute illness. The diagnosis of pseudogout is suggested by chondrocalcinosis on x-ray and synovial fluid showing rhomboid shaped, positively birefringent crystals under polarized light microscopy. __________ References: Calcium pyrophosphate deposition disease: clinical manifestations. (http://www.ncbi.nlm.nih.gov/pubmed/22303531) The mechanisms of inflammation in gout and pseudogout (CPP-induced arthritis). (http://www.ncbi.nlm.nih.gov/pubmed/22303529)

A 75-Year-Old Man Is Admitted to the Hospital with Fever