Lyme Arthritis in Children: Knee Swelling Without Rash

Lyme arthritis in children often appears as knee swelling weeks or months after a tick bite. Because the classic rash of early Lyme disease is frequently absent or unnoticed, diagnosis may be delayed.

Guardado and Sergent describe a case illustrating a common diagnostic gap: a 10-year-old girl with progressive right knee swelling was initially evaluated for other causes before Lyme arthritis was confirmed.

The delay occurred despite the child having documented tick exposure nine months earlier. The mother initially denied a tick bite history, but focused questioning revealed the child had ticks on her body months before symptoms appeared.

For a broader discussion of why Lyme disease is frequently overlooked in children, see Pediatric Lyme Disease: Why Children Are Often Misdiagnosed.

Initial Presentation: Knee Swelling From Lyme Arthritis

A 10-year-old girl presented with progressive right knee swelling and an unsteady gait. Physical examination revealed right knee effusion with decreased range of motion due to swelling.

The child walked with an unsteady gait but had no joint tenderness, crepitus, or overlying skin abnormalities. Notably, she had never developed a rash following the tick exposure nine months earlier.

The mother did not seek medical attention after the tick exposure because no rash appeared—representing a common missed opportunity for early diagnosis.

Testing Confirms Lyme Arthritis

A Western blot test for Lyme disease returned positive, confirming the diagnosis of Lyme arthritis. The positive test came despite the absence of erythema migrans rash and the significant time gap between tick exposure and symptom onset.

For more on why testing is important even without classic symptoms, see Lyme Disease Testing: Why Accuracy Matters.

“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 noted.

Typical Pattern of Lyme Arthritis in Children

Lyme arthritis most commonly affects children between ages 5 and 15, with the knee being the most frequently involved joint.

This child’s presentation—isolated knee swelling months after tick exposure—represents the classic pattern.

However, this pattern is often missed because parents expect immediate symptoms after a tick bite rather than joint swelling appearing months later.

The mono-articular presentation contrasts with juvenile idiopathic arthritis, which more commonly affects multiple joints.

Why Lyme Arthritis Is Often Missed in Children

Diagnostic delays occur for several reasons. Parents often assume that without a rash Lyme disease is unlikely.

Additionally, mono- or oligoarticular arthritis often leads clinicians to evaluate juvenile idiopathic arthritis, reactive arthritis, or orthopedic injury before considering infectious causes.

“When this diagnosis is missed, it can result in long-term morbidity, which is generally refractory to intravenous antibiotic therapy, oftentimes requiring synovectomy,” the authors warn.

Treatment and Complete Resolution

The child received two days of intravenous Rocephin (ceftriaxone) followed by 21 days of oral amoxicillin.

This treatment led to complete resolution of symptoms.

The rapid response to antibiotics confirms that early recognition and appropriate treatment can prevent the chronic joint damage that sometimes develops when Lyme arthritis goes untreated.

Warning Signs That Knee Swelling May Be Lyme Arthritis

Parents and clinicians should consider Lyme disease testing when a child presents with:

• Isolated knee swelling (most common joint affected)
• Living in or visiting Lyme-endemic areas
• History of outdoor exposure in wooded or grassy environments
• Swelling developing weeks to months after potential tick exposure
• Lack of response to standard anti-inflammatory treatments
• No history of trauma or injury
• Absence of fever or systemic illness

Even without a recalled tick bite or rash, these features warrant Lyme disease testing.

Frequently Asked Questions

Can Lyme disease cause knee swelling without a rash?

Yes. Lyme arthritis commonly presents as knee swelling months after the initial tick bite, often without a preceding rash.

How long after a tick bite can Lyme arthritis develop?

Lyme arthritis may develop weeks to months after infection. In this case, knee swelling appeared nine months after tick exposure.

Why is Lyme arthritis often missed in children?

Because parents and clinicians often assume Lyme disease requires a rash. Additionally, isolated knee swelling may initially be attributed to orthopedic injury or juvenile arthritis.

What happens if Lyme arthritis is untreated?

Untreated Lyme arthritis can cause persistent joint inflammation and long-term damage that may eventually require surgical intervention.

What is the treatment for Lyme arthritis in children?

Treatment typically involves antibiotics such as ceftriaxone followed by oral therapy like amoxicillin.

Should Lyme testing be done even without a known tick bite?

Yes. Many children do not recall a tick bite, and Lyme arthritis often develops months after exposure.