Dr. Arvikar and her colleagues are expanding the scope of their ongoing study by examining patients whose Lyme arthritis is milder than that of the initial population, including patients who haven’t yet received antibiotics. They are also evaluating more controls with inflammatory arthritis.
In a separate presentation, Dr. Kalish noted that Lyme arthritis, the manifestation of Lyme disease of greatest interest to rheumatologists, occurs in about 60% of untreated patients, with onset a mean of 6 months after the tick bite. It typically entails recurrent mono- or oligoarthritis of large joints. The knee is involved in roughly 95% of cases.
The natural history of untreated Lyme arthritis is a spontaneous resolution rate of 10%-20% per year. Since the 1980s, however, 4 weeks of oral doxycycline or amoxicillin has been the treatment of choice. About 10% of patients with Lyme arthritis continue to have active synovitis 3 months after their course of antibiotics.
“There are some patients you give the treatment to and their arthritis just melts away in a month, but some, no matter what you do with antibiotics, continue to have synovitis, often developing a highly proliferative palpable synovitis that is really gunked up and features obliterative microvascular lesions,” observed Dr. Kalish, a rheumatologist at Tufts University in Boston.
Dr. Kalish said that persistent posttreatment Lyme arthritis is most often due to a self-perpetuating immune response after the spirochete has been killed by antibiotics. He noted that patients with certain HLA-DRB1 haplotypes are more likely to experience persistent Lyme arthritis after standard recommended courses of antibiotics, and these DRB1 alleles correlate closely with the shared epitope associated with increased susceptibility to rheumatoid arthritis. Several candidate autoantigens have already been identified.