Lyme Arthritis in Children: Swollen Knee Without Rash
A swollen knee may be the first sign of Lyme arthritis in children
A tick bite or rash may not be remembered
Early recognition can prevent delayed diagnosis and unnecessary procedures
Lyme arthritis in children can be overlooked when a child develops knee swelling without a remembered tick bite or the classic bull’s-eye rash. In some cases, joint swelling may appear months after exposure, making the connection to Lyme disease less obvious.
A case report by Guardado and Sergent describes a child with unilateral knee swelling whose mother initially denied any history of a tick bite. However, after focused questioning, the mother recalled that the child had ticks on her approximately 9 months earlier.
Unfortunately, the child was not taken to her clinician at the time because she did not develop any skin rash that might have suggested Lyme disease.
This type of presentation is clinically important because many children with Lyme disease do not recall a tick bite, and not all patients develop or recognize an erythema migrans rash. A swollen knee, especially in a child living in or traveling through an endemic region, should raise concern for Lyme disease symptoms, including Lyme arthritis.
Child develops knee swelling months after tick exposure
The child demonstrated right knee effusion with decreased range of motion secondary to swelling. In addition, she had an unsteady gait without joint tenderness or overlying skin pathology.
A Western blot test for Lyme disease was positive.
Because Lyme arthritis is a late manifestation of infection, serologic testing is typically positive by the time arthritis develops. Laboratory findings, however, should always be interpreted in the context of the patient’s history, exposure risk, and clinical presentation.
“Lyme arthritis is a diagnosis that is often missed, even in children, who are the population with the highest incidence of Lyme disease,” the authors point out.
Why Lyme arthritis may be missed in children
Lyme arthritis often presents as monoarticular or oligoarticular arthritis. Children frequently have marked joint swelling despite relatively mild pain, a presentation that can delay recognition.
Although the knee is the joint most commonly affected, other large joints—including the ankle, elbow, wrist, shoulder, and hip—may also be involved. Some patients present with swelling that shifts from one large joint to another over time.
This presentation can make Lyme arthritis difficult to distinguish from other causes of pediatric joint swelling, including trauma, septic arthritis, transient synovitis, reactive arthritis, osteomyelitis, and juvenile idiopathic arthritis.
In children, the absence of a known tick bite or rash should not exclude the diagnosis. Tick bites can go unnoticed, and the initial rash may be absent, atypical, hidden, or forgotten by the time arthritis develops months later.
Lyme arthritis or juvenile idiopathic arthritis?
Differentiating Lyme arthritis from juvenile idiopathic arthritis (JIA) can be challenging because both conditions may present with persistent joint swelling and relatively little systemic illness. In Lyme-endemic regions, Lyme disease should remain in the differential diagnosis before a child is labeled with JIA.
Although Lyme serologic testing is typically positive once arthritis develops, no laboratory test is perfect. Test results should always be interpreted alongside the child’s exposure history, physical examination, and overall clinical presentation. A negative Lyme test alone should not automatically establish a diagnosis of JIA when clinical suspicion for Lyme disease remains high.
For additional information on testing limitations, see Lyme test accuracy.
Delayed diagnosis can increase the risk of complications
The authors warn that when Lyme arthritis is missed, it can lead to longer-term morbidity and, in some cases, persistent joint inflammation requiring more intensive treatment.
“When this diagnosis is missed, it can result in long-term morbidity, which is generally refractory to intravenous antibiotic therapy, oftentimes requiring synovectomy.”
Although synovectomy is rarely needed, the case underscores the importance of considering Lyme disease before moving toward invasive procedures in a child with unexplained knee swelling.
Children with a swollen joint should be evaluated carefully, particularly in Lyme-endemic areas. Clinical context, exposure history, physical examination, and appropriate testing all matter. For additional diagnostic context, see Lyme disease misdiagnosis.
Treatment and recovery
The child had complete resolution of symptoms following 2 days of IV Rocephin and 21 days of oral amoxicillin.
In clinical practice, many children with Lyme arthritis are treated initially with oral antibiotics, such as amoxicillin, doxycycline, or cefuroxime, consistent with current treatment guidelines. Intravenous ceftriaxone may be considered in selected cases, particularly when arthritis persists after appropriate oral therapy or when other manifestations of Lyme disease are present.
This case demonstrates the importance of including Lyme arthritis as part of the differential diagnosis of joint swelling, regardless of whether a tick bite is remembered.
Furthermore, the case raises awareness of monoarticular or oligoarticular arthritis as one of the signs of Lyme disease in children.
Frequently Asked Questions
Can Lyme disease cause one swollen knee in a child?
Yes. Lyme arthritis often affects one large joint, especially the knee. A child may have significant swelling with limited pain, making the diagnosis easier to miss.
Can Lyme arthritis occur without a rash?
Yes. A child may develop Lyme arthritis even if no rash was noticed. The rash may never appear, may be hidden, may look atypical, or may have resolved before arthritis develops.
How long after a tick bite can Lyme arthritis appear?
Lyme arthritis can develop weeks to months after infection. In this case, tick exposure was recalled only after focused questioning and had occurred approximately 9 months earlier.
Does a child need to remember a tick bite to diagnose Lyme arthritis?
No. Many children do not remember a tick bite. In endemic areas, unexplained joint swelling should prompt consideration of Lyme arthritis even without a known bite.
Does every child with Lyme arthritis need IV antibiotics?
No. Many children improve with oral antibiotics. IV ceftriaxone may be appropriate in selected cases, especially when arthritis persists or other clinical features suggest more complicated disease.
Clinical Takeaway
Lyme arthritis in children should remain on the differential diagnosis when a child presents with unexplained joint swelling, even if there is no remembered tick bite or rash.
A careful exposure history, including focused questions about tick exposure months earlier, can help identify cases that might otherwise be missed. Early recognition may prevent delayed treatment, unnecessary procedures, and prolonged joint inflammation.
Children with persistent swelling of one or more large joints who live in or have traveled to Lyme-endemic areas should be evaluated for Lyme disease, even when the presentation is atypical or a tick bite is not recalled.
Related Articles
Learn more about Lyme arthritis, pediatric Lyme disease, and diagnostic challenges in children.
Will steroid injections help children with Lyme arthritis of the knee?
Preventing unnecessary surgery for children with Lyme arthritis
Pediatric Lyme disease
Lyme disease misdiagnosis
Treatment for Lyme arthritis
References
- Guardado KE, Sergent S. Pediatric unilateral knee swelling: a case report of a complicated differential diagnosis and often overlooked cause. J Osteopath Med. 2022;122(2):105-109.
- Steere AC, Strle F, Wormser GP, Hu LT, Branda JA, Hovius JWR, Li X, Mead PS. Lyme borreliosis. Nat Rev Dis Primers. 2016;2:16090.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
My son has been suffering from Lyme for 5 years now. He has terrible knee pain and his gait has always been off for the past few years as well. The thing is his doctor does not think he has or had Lyme. Is there any treatment he can get for the pain?
I find a second opinion may help.
Could this happen in adults with Lyme as well? I am 57. Have been in and out of symptoms of Lyme since being diagnosed back in 2019. Was treated with longer term antibiotics, helped at first, but knee swelling and numbness still happening, seems worse in wet or humid weather. I hobble along with flare ups and sometimes need to use a walking stick or cane to help keep weight off it. Keep hoping it will get better, but it really doesn’t seem to improve. I wonder if it ever will. I have been getting so discouraged. The numbness and pins and needles sensation in the knee and thigh are difficult to deal with. Is anyone else going through this as an adult? Thanks.
I have also seen the problems in adults. I sometimes have had to change treatment.
My child is 4.5 and she has just finished 2 weeks of anti-biotics. However her knee seems to be worse now (taking longer each day before she starts to be active. Her gait is also seemingly completely off now when she is walking in-aided later in the day).
We have finished the prescribed 2 weeks. And will go back for further blood tests in another 2 weeks. Is it strange that symptoms have not subsided at all so far?
She has been taking Amoxicillin (Duomox).
I have patients who have not resolved their symptoms despite 2 weeks of antibiotics. The repeat test may not be all that helpful. The test may be negative due to antibiotics. Some doctors will not treat more than 2 weeks. Others do if their patient is still ill.
Thank you for your response. Is it the case that symptoms may well subside over more time, without further anti-biotics? In essence, should we be worried enough to bring forwards our next appointment on the basis of symptoms being worse now than at the start?
Some of my patient’s clear their symptoms over time. Others don’t. I am most concerned for my patients who have significant symptoms at the end of treatment.