A 52-year-old man comes to the emergency department with pain and swelling of his right knee for the last 24 hours. He has not traveled recently and has no recent history of injury or gastrointestinal or genitourinary infection. The patient was diagnosed with pulmonary sarcoidosis 5 years ago when he developed hilar lymphadenopathy and interstitial lung disease. His sarcoidosis responded to treatment with glucocorticoids and went into remission. He has been disease-free for the past 4 years. The patient also has a 10-year history of type 2 diabetes mellitus, hypercholesterolemia, and hypertension. Blood pressure is 140/86 mm Hg and pulse is 90/min. BMI is 34 kg/m². Physical examination is notable for a moderate-size effusion of the right knee with surrounding erythema and warmth. The knee joint is aspirated. Microscopic examination of the fluid is shown in the image below. Which of the following is the most likely etiology of this patient's joint effusion?

Question

Quizplus · Accepted Answer

Explanation: This patient has acute gouty arthritis. Gout usually presents with isolated attacks of intensely painful monoarthritis, with nearly 80% occurring in the metatarsophalangeal joints or knees. Patients also develop localized erythema and swelling, which is often mistaken for cellulitis. Synovial fluid in acute gout will show an inflammatory pattern, with a cloudy appearance, elevated leukocyte count (2,000-100,000 cells/mm³), and neutrophilic predominance. Under polarized microscopy, the synovial fluid will show monosodium urate crystals: ³ Needle shaped Negatively birefringent (appear yellow when lying parallel to the polarizing axis, and blue when lying perpendicular) Patients generally respond to nonsteroidal anti-inflammatory drugs (eg, indomethacin), colchicine, or corticosteroids (systemic or intraarticular). Long-term prophylactic medications (eg, allopurinol) are indicated for patients with recurrent attacks. (Choice A) Synovial immune complex deposition is seen in a variety of autoimmune (eg, systemic lupus erythematosus, rheumatoid arthritis) and viral (eg, parvovirus) arthritic conditions. Symptoms in these disorders are polyarticular and usually subacute to chronic. (Choice B) Fungal arthritis is usually due to infection with Candida species and is uncommon in nonimmunocompromised patients. Fungal arthritis in the majority of patients is preceded by recent invasive Candida infection, and onset of symptoms is less acute and dramatic than is seen in gout. (Choice C) In patients with gout, synovial crystals may be seen between flares, so the presence of these crystals alone does not rule out septic arthritis. Septic arthritis can cause acute monoarticular arthritis, but it is typically associated with fever, systemic manifestations (eg, chills), and progressively worsening symptoms over a few days, rather than the abrupt onset seen in gout. (Choice D) Calcium pyrophosphate dihydrate deposition (CPPD) can also cause an acute inflammatory arthritis ("pseudogout"), usually in the knee. Diagnosis is confirmed with synovial fluid analysis showing calcium pyrophosphate crystals. Compared to urate crystals, CPPD crystals are smaller, rhomboid-shaped, and weakly positively birefringent. CPPD crystals Educational objective: Acute gout presents as an acute monoarthritis, usually in the first metatarsophalangeal joint or knee. Synovial fluid analysis shows leukocytosis (2,000-100,000/mm³ with >50% neutrophils) and monosodium urate crystals, which are needle-shaped and negatively birefringent. ³ References: Diagnosis and treatment of gout in primary care. (http://www.ncbi.nlm.nih.gov/pubmed/22272526) Synovial fluid analysis for crystals. (http://www.ncbi.nlm.nih.gov/pubmed/21285711)

A 52-Year-Old Man Comes to the Emergency Department with Pain