Case Report: Histochemical and immunohistochemical characterization of a canine giant cell bone tumor in lumbar spine.

A 10-year-old sexually intact male Poodle dog, weighing 14 kg, was referred with abnormal gait (ataxia) and antalgic posture. The dog had a medical history of previous trauma and prostatitis diagnosed six months ago. Serum biochemical analysis showed elevated alkaline phosphatase and alanine aminotransferase levels. Neurological examination revealed hind limb dragging, body tilt, delayed proprioception-particularly affecting the left hind limb-and pain upon palpation of the lumbar region. Imaging diagnostic made evident a mass and a significant osteolysis of the second lumbar vertebra (L2), particularly on the left side of the vertebral body, extending into the first (L1) and third (L3) lumbar vertebrae. Necropsy findings confirmed the presence of a nodular soft mass below the left kidney and a firm mass compressing the medullary canal at L1-L3. Both masses exhibited whitish areas interspersed with blood-filled spaces. The tumor comprised numerous multinucleated giant cells of the osteoclastic type (positive for tartrate-resistant acid phosphatase- TRAP- and lysozyme), evenly distributed among mononuclear cells (both rounded and spindle-shaped). Alpha smooth muscle actin (SMA) was expressed in mononuclear cells, while IBA-1 staining highlighted mononuclear histiocytic cells. The final diagnosis was a primary lumbar extradural giant cell tumor of bone.