Original Article: Knee Pain in Adults and Adolescents: The Initial Evaluation

Issue Date: November 1, 2018

See additional reader comments at: https://www.aafp.org/afp/2018/1101/p576.html

To the Editor: This article did not mention Lyme disease as a possible factor in knee pain in adults and adolescents. In our rural health center in Maine, Lyme disease is the most common cause of acute noninjury-related knee pain and swelling, usually presenting as unilateral, red, and warm. It can also be transitory and migratory. Many patients are unaware of having had a tick bite.

Because early treatment of Lyme disease decreases the chance of chronic symptoms,¹ we often treat empirically with doxycycline while awaiting results of antibody testing. Travelers to high-risk areas may return home and develop symptoms weeks later. As the range of Lyme-bearing ticks keeps spreading, it is important for all physicians to keep this diagnosis in mind.

In reply: Thank you for your letter concerning additional regionally focused infectious etiologies for acute knee pain in primary care. We chose to categorize infections broadly, which made reviewing the various regional causes of knee pain beyond the scope of our article.

We agree that Lyme disease is endemic in certain parts of the United States and that it should be considered in the differential diagnosis for patients with arthralgia(s). We would welcome more literature about the incidence of Lyme disease–associated knee pain as a source of unilateral effusion.