Lyme disease: An underdiagnosed cause of mono-arthritis?


Welcome to another Inside Lyme Podcast with your host Dr. Daniel Cameron. In this episode, Dr. Cameron will be discussing the case of a 26-year-old man who was diagnosed with mono-arthritis after his clinical evaluation overlooked the possibility of Lyme disease.

The case was described by Marcelis and colleagues in a paper entitled “Lyme disease: A probably underdiagnosed cause of Mono-arthritis.”1

A 26-year-old man presented with acute knee pain. He recalled having similar knee pain occurring one year prior when he began walking for extended periods of time.

A magnetic resonance imaging (MRI) of the knee revealed a large joint effusion. He was not diagnosed or treated for Lyme disease.

Four months later, he had a follow-up MRI, which showed again a persistent joint effusion with diffuse enhancement, thickening of the synovium, enlarged lymph nodes in the popliteal fossa and enhancement of the soleus muscle.

He was subsequently evaluated again for acute knee pain that had been present for several days.  On further questioning, the 26-year-old man recalled a history of serologically confirmed Lyme disease.

“The combination of synovitis, lymphadenopathy in the popliteal fossa, and serology led to the diagnosis of Lyme mono-arthritis,” wrote the authors.

“Mono- and oligoarthritis is one of the most common manifestations [of Lyme disease], mostly affecting the knee, although the hip, ankle, elbow, and wrist may be affected.”

There was no evidence of septic arthritis.  The authors highlighted the need for a careful clinical history to avoid overlooking Lyme disease.

The following questions are addressed in this Podcast episode:

  1. What is synovitis?
  2. What is Lyme arthritis?
  3. What is septic arthritis?
  4. What manifestations of Lyme disease are there?
  5. Why is timely treatment of Lyme disease important?
  6. Could the treatment delay have been avoided?
  7. What are the therapeutic options?

READ MORE: Causes of treatment delays for Lyme disease

Thanks for listening to another Inside Lyme Podcast. Please remember that the advice given is general and not intended as specific advice to any particular patient. If you require specific advice, please seek that advice from an experienced professional.

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  1. Marcelis S, Vanhoenacker F. Lyme Disease: A Probably Underdiagnosed Cause of Mono-Arthritis. J Belg Soc Radiol. 2021;105(1):80. doi:10.5334/jbsr.2625



I fully intend to write an article on Lyme arthritis and various helpful treatments in the future but for now I’ll share what I’m personally doing and learning (briefly, it’s always conplicated!).

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