This report describes the presentation, diagnosis, treatment, and long-term outcome of a nine year old female spayed Yorkshire terrier with a protein-losing nephropathy. She was referred to Cornell after several episodes of shifting leg lameness and a positive Lyme result on an IDEXX 4Dx SNAP test. However, she presented to the ER Service at Cornell for a sudden onset of lethargy, anorexia, and pigmenturia. On physical examination, she had polyarthropathy, hypertension, and an infestation of Ixodes ticks. Laboratory tests showed a metabolic acidosis, hyperkalemsia, hyperphosphatemia, azotemia, hypoalbuminemia, isosthenuria, proteinuria, hyperfibrinoginemia, and systemic hypercoagulability. She was treated symptomatically for proteinuric renal disease, as well as for presumptive Lyme disease (Borreliosis), both arthritis and nephritis. After ruling out other likely differentials, she was started on mycophenolate therapy for presumptive immune complex-mediated glomerulonephritis. Over the next several months, she showed significant improvement in several renal values, including urine concentration, serum phosphorous, and degree of proteinuria (as measured by urine protein : creatinine ratio).