Rare Cause of Popliteal Cyst in Children

In this article four cases of Lyme disease presenting as a popliteal cyst in children are reviewed. A popliteal cyst is a fluid-filled sac behind the knee. The children all presented with chronic knee swelling but no other signs or symptoms.

This is a rare symptom for Lyme disease. Most patients present with a rash, flu-like illness, headache, or stiff neck. Single joint arthritis is not uncommon. The knee is affected most often. Some, but not all, patients are aware of a tick bite (the cause of Lyme disease). These four children had no awareness of a previous tick bite.

Treatment was with oral antibiotics. Symptoms did not go away for three of the four patients and intravenous antibiotics were needed. One child had a steroid injection when the antibiotics didn't clear up the joint swelling. Everyone was able to regain full knee motion.

The authors advise other physicians to consider Lyme disease as a possible diagnosis for children with popliteal cysts. This is especially true for children living in areas where Lyme disease occurs. Early diagnosis and treatment are needed to avoid long-term problems that can occur with this disease.