Presumptive Lyme disease-associated eosinophilic synovitis in a horse.

This research examines a 1-year-old horse that showed symptoms of infection from Lyme disease. During treatment, it was found that the horse suffered from a new variety of synovitis, potentially caused by the Borrelia burgdorferi bacteria.

Animal Patient and Initial Symptoms

• The patient was a 1-year-old American Quarter horse who was brought to the vets due to acute onset of right hind lameness, a symptom typically associated with a leg or joint injury.
• During a physical examination, a swelling of the right tarsocrural joint, the joint at the hock of a horse’s hind leg, was observed. This condition is known as synovial effusion.

Further Examination and Initial Treatment

• The next step was to perform a cytological analysis on the synovial fluid from the affected horse’s joint. This involved microscopically examining the cells within the fluid. The results revealed a high occurrence of eosinophils, a type of white blood cell, implying the horse was suffering from amplified eosinophilic synovitis, inflammation of the joint due to eosinophils.
• While the blood tests – serology – revealed that antibodies against Borrelia burgdorferi bacteria were present, suggesting both acute and chronic infection, the PCR test of the synovial fluid didn’t detect any DNA from the bacteria.
• When it comes to diseases in horses, an unusual aspect of this report is the eosinophilic synovitis observed, an inflammation infrequently seen in horses.
• The filly was treated with phenylbutazone, a nonsteroidal anti-inflammatory drug, and oxytetracycline, a broad-spectrum antibiotic. The usage of two different types of antibiotics suggested a bacterial infection.

Final Treatment and Conclusion

• Despite initial improvement, the horse had a relapse of lameness eight months later, afflicting both hind legs but without any radiographic abnormalities.
• Synovial cytology this time displayed indications of macrophagic synovitis, meaning there was an excessive concentration of macrophages, another type of white blood cell, but no eosinophils.
• The horse was then discharged after prescribed a 14-day course of minocycline, another type of antibiotic, resulting in a complete recovery.
• While the link between the eosinophilic synovitis the horse initially presented and the Lyme disease it apparently suffered wasn’t definitively established, the researchers theorized that there was very likely a connection as the horse responded positively to antibiotics, implying a bacterial disease.