Lyme Pseudothrombophlebitis in a Young Child: A Missed Diagnosis

Lyme pseudothrombophlebitis in a young child can mimic more common conditions such as muscle injury or deep vein thrombosis (DVT), leading to delayed diagnosis.

The pain had been ongoing for one week. “He described the pain as throbbing, worse with movement, and improved with rest,” writes Sandelich and colleagues. Three days earlier, the boy had visited a different emergency department and was diagnosed with a muscle sprain following results from an X-ray.

When symptoms persist despite an initial diagnosis, further evaluation is critical.

The boy’s pain continued, and an ultrasound of the lower extremity was obtained. It revealed “a 13 x 6 x 2.7-cm heterogeneous mass with solid and cystic components in the left calf,” writes Sandelich.

An MRI showed findings consistent with a large collection in the left gastrocnemius muscle with surrounding myositis.

Diagnosis: Lyme Pseudothrombophlebitis

A Lyme Western blot test was positive, and the child was diagnosed with Lyme pseudothrombophlebitis.

He was treated successfully with intravenous cefazolin, followed by 4 weeks of amoxicillin.

“A known complication of a ruptured popliteal cyst is pseudothrombophlebitis,” explains Sandelich. A popliteal (Baker’s) cyst has been reported in Lyme disease.

Why This Case Matters

The authors caution that this presentation can closely resemble deep venous thrombosis (DVT), making imaging essential.

The clinical presentation in this case is similar to that of DVT, and obtaining an ultrasound of the deep leg veins is imperative.

Learn more about Lyme disease testing and diagnosis and why atypical cases are often missed.

Clinical Perspective

Lyme disease can present with unusual musculoskeletal and vascular findings, particularly in children.

When symptoms do not follow the expected course—or fail to improve with standard treatment—clinicians should consider alternative diagnoses, including Lyme disease.