how do I diagnose and manage Lyme disease in a seropositive dog with clinical signs?

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Diagnosis of clinical Lyme borreliosis requires the combination of compatible clinical signs, tick exposure history, positive serology, and exclusion of other causes — no single test is sufficient. 46 Clinical signs that support the diagnosis include fever, shifting limb lameness, arthritis, arthralgia, anorexia, and lymphadenopathy. 41 Lyme nephritis, the most serious manifestation, presents with protein-losing nephropathy and carries a frequently fatal prognosis despite treatment. 113 In a seropositive dog with protein-losing nephropathy, features that add diagnostic weight to Lyme nephritis specifically include retriever or retriever-mix breed, azotemia, hyperkalemia, hyperphosphatemia, thrombocytopenia, anemia, neutrophilia, and urinary findings of hematuria, glucosuria, and pyuria with a negative urine culture. 5 Serological testing centers on the C6 peptide antigen assay, which detects antibodies to the VlsE surface protein expressed only during active host infection. 54 The in-clinic qualitative C6 test is the standard first-line screen; a quantitative C6 ELISA can follow to establish a baseline titer. 4 Quantitative titers have specific value in clinical disease because decreasing titers may signal response to antibiotic treatment. 1 Antibodies can remain elevated for up to 17 months after infection, so a positive titer alone does not confirm active disease. 4 All seropositive dogs with clinical signs should have urinalysis performed as a minimum database to screen for proteinuria. 13 In dogs with proteinuria, urine protein:creatinine ratio, serum biochemistry panel, and complete blood count are indicated to characterize the severity of nephropathy and identify the clinicopathologic features of Lyme nephritis described above. 5 For dogs with Lyme arthritis, doxycycline is the standard antibiotic treatment. 3 Signs of Lyme arthritis are transient or respond quickly to oral antibiotics. 3 No antibiotic is formally approved for canine Lyme disease, and the opti