A 33-year-old woman comes to the office due to a 2-day history of severe left knee pain and swelling. She has had no trauma, pain in other joints, fever, chills, or rash. The patient has a history of parathyroid adenoma with primary hyperparathyroidism and underwent parathyroidectomy a week ago. Her other medical problems include moderate persistent asthma, irritable bowel syndrome, and gastroesophageal reflux disease. The patient does not use tobacco, alcohol, or illicit drugs. She is married and her only medication is an oral contraceptive.
Temperature is 36.7 C (98 F) , blood pressure is 110/56 mm Hg, pulse is 67/min, and respirations are 14/min. BMI is 28 kg/m². Physical examination shows a moderate left knee effusion with warmth, erythema, and tenderness. Range of motion of the knee is decreased due to pain.
Laboratory results are as follows:

Analysis of synovial fluid from the knee joint shows a leukocyte count of 20,400/mm³ with 80% neutrophils.
Which of the following is the most likely cause of this patient's knee pain?

Question

A 33-year-old woman comes to the office due to a 2-day history of severe left knee pain and swelling. She has had no trauma, pain in other joints, fever, chills, or rash. The patient has a history of parathyroid adenoma with primary hyperparathyroidism and underwent parathyroidectomy a week ago. Her other medical problems include moderate persistent asthma, irritable bowel syndrome, and gastroesophageal reflux disease. The patient does not use tobacco, alcohol, or illicit drugs. She is married and her only medication is an oral contraceptive.
Temperature is 36.7 C (98 F) , blood pressure is 110/56 mm Hg, pulse is 67/min, and respirations are 14/min. BMI is 28 kg/m². Physical examination shows a moderate left knee effusion with warmth, erythema, and tenderness. Range of motion of the knee is decreased due to pain.
Laboratory results are as follows:

Analysis of synovial fluid from the knee joint shows a leukocyte count of 20,400/mm³ with 80% neutrophils.
Which of the following is the most likely cause of this patient's knee pain?

Quizplus · Accepted Answer

11ec193a_9913_c606_853d_f9811e69fd55_MD0002_00 This patient has acute, inflammatory monoarticular arthritis affecting the knee. In light of her history of hyperparathyroidism and recent parathyroidectomy, this is most likely due to calcium pyrophosphate dihydrate crystal arthritis (pseudogout). Hyperparathyroidism can lead to chondrocalcinosis in the articular cartilage; parathyroidectomy can precipitate a pseudogout attack due to an abrupt drop in serum calcium levels, which triggers crystal shedding into the synovial fluid. Pseudogout commonly affects the knees, where it may be difficult to distinguish from urate gout. It also frequently affects the wrists and ankles and may involve multiple joints concurrently. Attacks often occur in the setting of trauma/overuse, surgery, or medical illness. The primary treatment is nonsteroidal anti-inflammatory drugs; intra-articular glucocorticoids and colchicine can also be considered. (Choice A) Although gout can also present with monoarthritis, this patient has no risk factors for gout (eg, obesity, alcohol use), and her recent parathyroidectomy is more strongly associated with pseudogout. (Choice B) Erosive osteoarthritis typically occurs in patients age >40. It presents with pain and stiffness, crepitus and tenderness on examination, joint space narrowing on x-rays, and clear synovial fluid with <2,000/mm³ white blood cells. ³ (Choice C) Osteitis fibrosa cystica is a rare complication of severe primary hyperparathyroidism characterized by subperiosteal bone resorption in the middle phalanges, tapering of the distal clavicles, "salt and pepper" appearance of the skull, bone cysts, and brown tumors of the long bones. Patients typically experience chronic bone pain rather than acute arthritis (as in this patient). (Choice E) Septic arthritis typically presents with markedly decreased range of motion, increased warmth and swelling, and cloudy joint aspirate with >100,000/mm³ white blood cells (predominantly neutrophils). ³ Educational objective: Pseudogout causes an acute inflammatory arthritis, most commonly in the knees. Parathyroidectomy can precipitate a pseudogout attack due to an abrupt drop in serum calcium levels, which triggers shedding of calcium pyrophosphate dihydrate crystals into the synovial fluid. __________ References: Risk factors for pseudogout in the general population. (http://www.ncbi.nlm.nih.gov/pubmed/22886340)

A 33-Year-Old Woman Comes to the Office Due to a 2-Day