What is your diagnosis?

A 4-year-old 19-kg (42-lb) spayed female mixed-breed dog was evaluated for progressive pelvic limb weakness, lameness of 10 weeks’ duration, and urine retention. The dog was housed indoors and outdoors. Its vaccination status was not current, and the dog had not received parasitic prophylaxis. Physical examination revealed pelvic limb muscle atrophy and a firm, 6 X 7 X 3-cm swelling on the medial aspect of the right thigh, close to the inguinal region; the mass was consistent with an inguinofemoral lymph node. The perineal region was symmetrically swollen. Pain was elicited on extension of each pelvic limb. No abnormalities were detected on neurologic examination. Findings on CBC included normocytic and normochromic anemia (RBC count, 4.80 X 1012 RBCs/L [reference range, 5.5 X 1012 RBCs/L to 8.5 X 1012 RBCs/L]; hemoglobin, 21 g/dL [reference range, 12 to 18 g/dL]; Hct, 33% [reference range, 37% to 55%]). Plasma biochemical analysis revealed hypoalbuminemia (albumin, 1.84 g/dL; reference range, 2.6 to 3.3 g/ dL), hyperglobulinemia (globulins, 9.8 g/dL; reference range, 2.7 to 4.4 g/dL), and hypercalcemia (total calcium, 11.9 mg/ dL; reference range, 9 to 11.3 mg/dL). Serum creatinine and BUN concentrations were 0.57 mg/dL (reference range, 0.50 to 1.5 mg/dL) and 28.4 mg/dL (reference range, 21.4 to 60 mg/dL), respectively. Urinalysis revealed proteinuria and a high urine specific gravity (1.055). Serum electrophoresis revealed high serum protein concentrations (γ-globulin, 48.4 g/dL [reference range, 8.0 to 18.0 g/dL]; α2 globulin, 13.9 g/dL [reference range, 5.0 to 12.0 g/dL]). N