A Good Walk Spoiled

Patient History A 64 year old man from New Jersey presents to his primary care physician complaining of a swollen left knee. He states that it started after 18 holes of golf about 1 week ago, but has not been bad enough to keep him off the golf course. He denies any fever, traumatic injury, or other systemic symptoms. Physical exam is significant for a warm tender left knee with swelling.

Differential Diagnosis: Single Swollen Joint Trauma Arthritis  Infection: -Disseminated gonococcus -Lyme disease -Septic arthritis (commonly Staphylococcus aureus) Gout or pseudogout (uric acid or calcium pyrophosphate dihydrate crystals in the joint)   Systemic autoimmune diseases such as psoriasis and rheumatoid arthritis

Infectious vs. Non-infectious: Role of Joint Aspiration The patient’s doctor was most concerned about gout or an infection so he sent aspirated joint fluid for the following tests: Cell counts: Identifies the number of white blood cells in the fluid (high numbers with many neutrophils favor septic arthritis). Gram stain and culture: Allows for identification of typical bacteria that cause septic arthritis (commonly S. aureus and Streptococcus species). Fluid smear : Microscopic examination of fluid for the presence of crystals.

Patient Results Gram stain: Many white blood cells, no organisms seen Culture: No growth Neutrophils on Gram stain of joint fluid Cell counts: 34, 800 cells/mm3 81% neutrophils 8 % lymphocytes 11% monocytes Fluid smear: No crystals identified

Laboratory Results Narrow the Differential Trauma Osteoarthritis Systemic auto-immune diseases  Infection: -Disseminated gonococcus -Lyme disease -Septic arthritis (commonly S. aureus) WOULD HAVE GROWN IN CULTURE Gout or pseudogout (uric acid or calcium pyrophosphate dihydrate crystals in the joint)   NO CRYSTALS SEEN HIGH WHITE COUNT WITH INCREASED NEUTROPHILS MAKES THESE UNLIKELY

Laboratory Results Narrow the Differential Disseminated gonococcus Caused by bacteria Neisseria gonorrhoeae. Needs enriched media to grow in laboratory culture. Lyme disease Caused by the spirochete (bacteria) Borrelia burgdorferi transferred to humans after a tick bite. Cannot be cultured by routine methods. The patient’s doctor thought Lyme disease was the most likely culprit given the laboratory results and the patient’s history of outdoor exposure and location.

Additional Testing: Lyme Immunoblot The presence of antibodies against multiple Borrelia burgdorferi antigens in the patient’s serum is indicative of past or current infection. Positive Lyme IgG Immunoblot For more information about interpretation of Lyme Immunoblot visit: http://www.cdc.gov/lyme/diagnosistesting/LabTest/TwoStep/WesternBlot/index.html

Additional Testing: B. burgdorferi PCR Polymerase chain reaction (PCR) testing of the joint fluid is positive indicating the presence of the bacteria that causes Lyme disease at the site of swelling. A positive immunoblot alone cannot always distinguish past from current infection. PCR testing helps implicate B. burgdorferi as the cause of the current disease.

Final Diagnosis Lyme disease: Late Disseminated Stage Patients with untreated Lyme disease may experience joint pain and swelling months-years after the initial Tick bite. The patient was treated with antibiotics (doxycycline) and reported feeling better within 2 weeks.

Summary Joint pain and swelling is a common complaint. Some infectious causes cannot be easily cultured and identified in the lab. In the case of Lyme disease a combination of antibody testing and nucleic acid detection can help provide a definitive diagnosis. Created by Laurel Glaser, Ph.D. CPEP Fellow University of Pennsylvania

Laurel Glaser, M.D., Ph.D. Dr. Glaser is second year CPEP fellow at the Hospital of the University of Pennsylvania. Dr. Glaser completed the Medical Scientist Training Program at The Mount Sinai School of Medicine and subsequently trained in Anatomic and Clinical Pathology at University of Pennsylvania. Her research interests include respiratory viruses and antimicrobial resistance detection.