3-month history of progressive left pelvic limb swelling
15-year-old female spayed domestic long hair presented for a 3-month history of a progressive swelling of the left pelvic limb. The patient was hit by a car in 2012 and had a left tibial fracture repaired with an intra-medullary pin and medial plate and screws.
Physical exam revealed a weight bearing lameness of the left pelvic limb and soft tissue swelling of the left tibial region with purulent exudate from a draining tact site over the left medial tibial region. A grade 2/6 parasternal systolic murmur was also noted.
CBC showed a mild anemia and moderate inflammatory leukogram. Chemistry panel showed moderate azotemia (BUN 136, Cre 4.4), hyperglobulinemia, and severe hyperphosphatemia.
Radiographs of the swollen limb were made; plus, three views of the thorax (five images total, all in the carousel above).
The patient underwent surgery for a left pelvic limb amputation at the level of the coxofemoral joint. Histopathology of the left hind soft tissue mass was suggestive of an aggressive round cell neoplasm with evidence of metastasis to the popliteal lymph node. Further special staining with MUM1 stain confirmed plasmablastic plasma cell tumor, with expected aggressive clinical behavior.
The patient continued to do well after surgery and was referred to the oncology department for staging and treatment. The abdominal ultrasound was performed 18 days after the initial presentation. Unfortunately, due to evidence of metastatic lymphadenopathy in the abdomen, the owner elected not to pursue further treatment due to poor prognosis.
Plasma cell tumors such as multiple myeloma are extremely rare in cats. It is estimated that <1% of all malignant neoplasms in cats are diagnosed as multiple myeloma.1 Commonly, lesions from multiple myeloma will occur as focal lytic lesions within the ribs, spine, pelvis and long bones and metastasize to extramedullary sites like the liver, spleen and lymph nodes. To date, there is no literature specifically available on plasmablastic plasma cell tumor in cats, let alone literature of these tumors being associated with implants. However, there are documented cases of other round cell tumors being associated with implants. There is a reported case of a cat that developed boney lysis and soft tissue swelling of the right forelimb. The swelling surrounded a previously implanted surgical plate along the distal radius 5 years prior to presentation. This cat was diagnosed with non-epitheliotropic T-cell cutaneous lymphoma with confirmed regional lymph node involvement.2 Although the latter case had bone involvement, there is ample literature supporting the development of neoplasms at the site of foreign material in dogs, cats, and humans without bone involvement. Several cases of sarcomas developing at the site of microchip implantation have been described in dogs, cat, rodents and zoo animals.3 Feline injection site sarcomas are very well documented and have been recognized for over 20 years.4 In humans, breast implant associated anaplastic large cell lymphoma is also very clearly understood.5 Cutaneous tarsal lymphoma has been reported in cats but it was not a differential for this case as this neoplasm did not involve the tarsus, nor were the biopsy results consistent with lymphoma.
Implant associated tumors have also been described in dogs. The medium time to diagnosis from time of implant was about 5.5 years; ranging 9 months to 10 years.6 The vast majority of implant associated osteosarcomas occurred in the diaphyseal region of the bone.6
Fibrosarcomas and undifferentiated sarcomas have also been reported in cats and dogs, albeit much less common than osteosarcoma.7 In this patient’s pelvic limb radiograph, the mass clearly follows the tibia and abruptly narrows proximal to the tarsus where the intramedullary pin terminates. One study demonstrated osteomyelitis and neoplasia associated with the use of Jonas intramedullary splints. Of 11 cases, 5 cases had developed tumors in close proximity to the splint.8 Although corrosion was evident in these implants, the study still supports the association between the development of neoplasia at the location of the surgical implant. Another study in rats demonstrated a direct correlation between presence of orthopedic implants and development of sarcoma and lymphoma. In this same study, intramedullary pins were associated with increased prevalence of neoplasia further supporting that the location of the implant plays a role in the development of malignancies.9 In the current case report, the location of the tumor and its relationship to the implant, and length of time to tumor development is consistent with the features of numerous publications of implant associated neoplasms. However, further exploration is required to better understand the role of the variable types of malignant transformations associated with orthopedic implants.
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