What’s causing this lady’s confusion and knee pain?
Hint: it isn’t dementia or arthritis
Vol.20, No.05, August 2012

Mrs. LA, an 84-year-woman who lives in a rest home, presents to the ED with confusion and a decreased level of consciousness. She’d been to the ED two weeks prior complaining of knee pain. She was reassured that it was likely arthritis and sent home.

She then saw her FP 3 days later with severe knee pain. He ordered x-rays of the knees. The pain recurred about 5 days later and she presented to the hospital with a BP of 197/150 and severe knee pain, but this time she also had a right facial droop, which resolved in the ER. She was referred to the urgent neurology clinic and seen 2 days later. When Mrs. LA’s presented there, she had confusion and a decreased level of consciousness and was referred to the ER, as the neurologist didn’t think it was a stroke but rather a metabolic problem. Again the patient cried in pain when her left knee was moved, but on examination there was no tenderness or swelling. X-rays of the knee, hip and back were normal. In the ER, blood work was done including CBC, electrolytes and liver function tests. All were normal. On examination she appeared confused. Head and neck exam were normal. CV exam showed normal heart sounds and no murmurs. Her respiratory and GI exams were also normal. She had no pedal edema. Her vital signs were normal but a urine dip showed 100 leukocytes.

The patient was started on cefazolin and seemed to improve in 24 hrs. By 48 hours, however, Mrs. LA developed acute delirium and was extremely distraught, confused and complained of right knee pain again, along with pain in all of her joints. Blood work including CBC and electrolytes proved normal. Her vital signs remained normal as well. The following day a diagnostic test came back abnormal, and clarified the diagnosis.

Do you know the cause of Mrs. LA’s confusion and knee pain?

ANSWER

Mrs. LA had a transthroracic echocardiogram (TTE) that revealed the diagnosis. There was a query abcess over the mitral valve. The detailed TTE showed vegetative lesions over the mitral valve, indicating infective endocarditis (IE). The patient did not have any of the traditional risk factors, which include IV drug use or prosthetic heart valve. IE has been increasing in incidence in North America and the most common causative organisms are S. aureus (28%) and Viridans Streptococcus (21%), followed by Enterococci. Mrs. LA was started on ceftriaxone and improved rapidly in hospital with complete resolution of her neurological symptoms and acute knee pain. The infectious disease specialist elected to keep her on IV ceftriaxone for a total of six weeks. Within a few days she was discharged and back at her baseline level of functioning.

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