Popliteal Cyst With Positive Antinuclear Antibodies as the Presentation of Lyme Disease

To the Editors: Popliteal cysts as manifestations of disseminated Lyme disease in pediatric patients are exceedingly rare; only 4 previous reports have been made in the orthopedic and rheumatology literature.1–4 We present the case of an adolescent male with over a month of posterior knee pain and a popliteal cyst, ultimately found to be secondary to disseminated Lyme disease. A 14 year-old male with autism spectrum disorder was presented to the Orthopaedic Surgery Clinic with a 1 month history of vague left posterior knee and calf pain. His mother denied trauma to the region, previous tick bites, recent travel, skin rashes or illness. He had full range of motion without significant swelling anteriorly but displayed fullness over the posterior knee. The patient had been seen previously in the emergency department at an outside facility and was worked up for thrombophlebitis or deep venous thrombosis (DVT) of the affected extremity; ultrasound was negative for DVT, but the patient’s D-dimer levels were elevated. He presented to his primary care provider several days later without improvement in the swelling, and repeat ultrasound at that time was again negative for DVT. A noncontrast magnetic resonance imaging study obtained revealed a 5 × 3 × 17 cm cystic structure extending along the posteromedial aspect of the lower leg, originating from the synovium of the knee (see Fig., Supplemental Digital Content 1, https://links.lww.com/INF/C65). Initial working diagnosis was Baker’s cyst, and the patient was subsequently referred to our Pediatric Orthopaedic Clinic for further evaluation and management. Repeated magnetic resonance imaging demonstrated some reduction in the size of the popliteal cyst, but the patient continued to complain of pain and swelling. Aspiration of both the cyst and arthrocentesis of the ipsilateral knee was completed in clinic; cell count and culture of both fluids were within normal reference ranges. Serum tests were drawn at the time, including a screening laboratory test for Lyme antibody as well as an antinuclear antibody panel. Both the Lyme screening test and the antinuclear antibody panel returned positive, and the patient’s serum sample was sent for Western blot analysis to confirm the diagnosis of Lyme disease, which was positive. The patient was referred to the Pediatric Infectious Disease Clinic and placed on oral doxycycline for 4 weeks. At most recent follow up, the patient’s symptoms have improved substantially. Although popliteal cysts are common in pediatric patients, the presentation of Lyme disease as an isolated popliteal cyst has only rarely been reported in the literature. Two of the 4 manuscripts we found have been published within the last decade,1–4 potentially suggestive that unusual presentations of the disease may be increasingly recognized. Lyme arthritis may mimic other rheumatic or inflammatory conditions, and juvenile idiopathic arthritis has also been shown to have an association with the development of popliteal cysts.5 An interaction between the diagnostic tests for some rheumatic conditions and Lyme disease has also been previously demonstrated,6 thereby further obfuscating the clinical picture. Treatment for Lyme popliteal cysts may also be challenging, and this case highlights the absolute necessity of a high index of suspicion for Lyme disease in all pediatric patients with arthritic or unilateral musculoskeletal complaints—particularly those patients in the northeastern United States or eastern Canada, regardless of insect bite or recent travel history. Unusual presentations of the disease, in conjunction with unclear laboratory findings, can delay treatment and lead to worse clinical outcomes. It is crucial that this provider population may be aware of the myriad manifestations of Lyme disease, so that treatment can be initiated promptly and without delay. Theodore J. Steelman, MD Scott C. Wagner, MD Jefferson W. Jex, MD Department of Orthopaedics Walter Reed National Military Medical Center Bethesda, Maryland Division of Orthopaedics Department of Surgery Uniformed Services University of the Health Sciences Bethesda, Maryland

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.