What Is Your Diagnosis?

Kathryn L. Phillips Department of Structure and Function, Diagnostic Imaging, School of Veterinary Medicine, Ross University, Basseterre, Saint Kitts and Nevis, West Indies.

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Richard B. Page Department of Structure and Function, Diagnostic Imaging, School of Veterinary Medicine, Ross University, Basseterre, Saint Kitts and Nevis, West Indies.

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History

A 24-kg (52.8-lb) 22-month-old sexually intact female pit bull–type dog was referred for evaluation because of lack of appetite and swelling around the right carpus and right stifle joint with associated lameness of 1 month's duration. The patient had been empirically treated with amoxicillin (20 mg/kg [9.1 mg/lb], PO, q 12 h) for 4 weeks. During physical examination, the patient had a body temperature of 40°C (104°F), appeared lethargic, and was overtly lame (only toe touching) on the right thoracic limb. There was firm swelling at the distal aspect of the right antebrachium and on the medial aspect of the right stifle joint. The right stifle joint had palpable synovial effusion. Findings of a CBC and serum biochemical analysis were within reference limits. The patient was treated with analgesic and anti-inflammatory medication. Radiographs of the right carpus and right stifle joint were obtained (Figure 1).

Figure 1—
Figure 1—

Radiographic views of the right carpus (mediolateral [A] and dorsopalmar [B]) and right stifle joint (mediolateral [C] and craniocaudal [D]) of a 22-month-old sexually intact female pit bull–type dog evaluated because of fever, lack of appetite, and swelling around the right carpus and right stifle joint with associated lameness of 1 month's duration.

Citation: Journal of the American Veterinary Medical Association 241, 7; 10.2460/javma.241.7.877

Determine whether additional imagining studies are required, or make your diagnosis from Figure 1then turn the page

Radiographic Findings and Interpretation

Aggressive bone lesions are evident at the distal metaphysis of the right radius and ulna and the proximal metaphysis of the right tibia (Figure 2). The lesions were characterized by proliferative amorphous periosteal reaction, permeative lysis of the parent bone with disruption of the cortices, and swelling of associated soft tissues. The radiographic diagnosis was polyostotic aggressive bone lesions with multiple limb involvement. The differential diagnoses for polyostotic aggressive bone lesions include bacterial or fungal osteomyelitis and neoplasia.

Figure 2—
Figure 2—

Same radiographic images as in Figure 1. Notice the aggressive bone lesions (arrows) at the distal metaphysis of the right radius and ulna (A and B) and the proximal metaphysis of the right tibia (C and D). The lesions are characterized by proliferative amorphous periosteal reaction, permeative lysis of the parent bone with disruption of the cortices, and swelling of associated soft tissues.

Citation: Journal of the American Veterinary Medical Association 241, 7; 10.2460/javma.241.7.877

Treatment and Outcome

In this patient, metastatic skeletal neoplasia was considered the most likely differential diagnosis. Staging was based on findings for 3-view orthogonal thoracic radiographs, 2-view orthogonal radiographs of the contralateral carpus and stifle joint, and abdominal ultrasonography. No other important abnormalities were detected. The patient was anesthetized for collection of bone biopsy specimens of the right tibia and right radius. The histopathologic diagnosis was osteoblastic osteosarcoma. The owners elected to have the dog euthanatized. Findings on postmortem examination were consistent with the results of the radiologic and histologic examinations. The 2 large aggressive bone lesions did not cross adjacent joints, and articular cartilage was normal in appearance. No other bony abnormalities were detected. The lungs appeared grossly normal, but a single histologic section of the lungs contained 1 venule that was distended with neoplastic cells and osteoid, representing micrometastasis.

Comments

Lesions that affect multiple bones are often the result of hematogenous dissemination or multiple penetrating wounds. Given that the patient had no history of trauma, no visible evidence of penetrating wounds or draining tracts, and no abnormalities detected via a CBC, bacterial osteomyelitis was considered unlikely.

In geographic locations where fungal disease is endemic or for a patient with travel history to these areas, fungal osteomyelitis is a prioritized differential diagnosis. Fungal disease is not endemic in Saint Kitts, and the patient did not have a travel history or clinical signs consistent with disseminated fungal disease. Although histopathologic findings are necessary for a final diagnosis, fungal osteomyelitis was considered less likely because of the geographic location.

The most common cause for a monostotic aggressive bone lesion at the metaphysis in veterinary patients is a primary bone tumor. Primary bone tumors can invade multiple bones by direct extension or hematogenous distribution. Lesions that are hematogenous or metastatic in origin typically occur at the diaphysis around the nutrient foramen or at the metaphysis because of the intricate capillary network in this area.1 Osteosarcoma, hemangiosarcoma, and soft tissue carcinomas are all known to metastasize to additional skeletal sites.2

Osteosarcoma is a highly metastatic disease that disseminates through hematogenous routes; the most common sites for metastases are the lungs and appendicular skeleton.3 At the time of diagnosis, all osteosarcoma cases should be considered to have microscopic metastatic disease. Skeletal metastases typically develop following the surgical removal of the primary tumor. This case represents the simultaneous development of 2 aggressive bone lesions of similar size. The lesion at the distal aspect of the antebrachium incorporating both the radius and the ulna is considered a single tumor that has locally invaded the adjacent bone. Synchronous multicentric osteosarcoma is rarely reported in veterinary medicine.4 It is debated in the human literature that multicentric synchronous osteosarcoma likely represents an extreme example of metastatic disease rather than multiple primary tumors.5 However, they cannot be definitively distinguished and both are associated with a grave prognosis. Radiography is a valuable tool to detect aggressive bone lesions, but the definitive diagnosis requires histologic evaluation. In addition to evaluating for pulmonary metastases, radiography can be used to assess skeletal metastatic disease. However, the most sensitive tests for skeletal metastatic disease are nuclear scintigraphy and CT.

  • 1.

    Thrall DE. Bone tumors versus bone infections. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 5th ed. Philadelphia: WB Saunders Co, 2007;306313.

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  • 2.

    Thompson KG, Pool RR. Tumors of bone. In: Meuten DJ, ed. Tumors in domestic animals. 4th ed. Ames, Iowa: Iowa State Press, 2002;266314.

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    • Export Citation
  • 3.

    Spodnick GJ, Berg J, Rand WM, et al. Prognosis for dogs with appendicular osteosarcoma treated by amputation alone: 162 cases (1978–1988). J Am Vet Med Assoc 1992; 200:79957999.

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    • Export Citation
  • 4.

    Hoeneroff MJ, Kiupel M, Rosenstein D, et al. Multipotential osteosarcoma with various mesenchymal differentiations in a young dog. Vet Pathol 2004; 41:264268.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5.

    Daffner R, Kennedy S, Fox K, et al. Synchronous multicentric osteosarcoma: the case for metastases. Skeletal Radiol 1997; 26:569578.

  • Figure 1—

    Radiographic views of the right carpus (mediolateral [A] and dorsopalmar [B]) and right stifle joint (mediolateral [C] and craniocaudal [D]) of a 22-month-old sexually intact female pit bull–type dog evaluated because of fever, lack of appetite, and swelling around the right carpus and right stifle joint with associated lameness of 1 month's duration.

  • Figure 2—

    Same radiographic images as in Figure 1. Notice the aggressive bone lesions (arrows) at the distal metaphysis of the right radius and ulna (A and B) and the proximal metaphysis of the right tibia (C and D). The lesions are characterized by proliferative amorphous periosteal reaction, permeative lysis of the parent bone with disruption of the cortices, and swelling of associated soft tissues.

  • 1.

    Thrall DE. Bone tumors versus bone infections. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 5th ed. Philadelphia: WB Saunders Co, 2007;306313.

    • Search Google Scholar
    • Export Citation
  • 2.

    Thompson KG, Pool RR. Tumors of bone. In: Meuten DJ, ed. Tumors in domestic animals. 4th ed. Ames, Iowa: Iowa State Press, 2002;266314.

    • Search Google Scholar
    • Export Citation
  • 3.

    Spodnick GJ, Berg J, Rand WM, et al. Prognosis for dogs with appendicular osteosarcoma treated by amputation alone: 162 cases (1978–1988). J Am Vet Med Assoc 1992; 200:79957999.

    • Search Google Scholar
    • Export Citation
  • 4.

    Hoeneroff MJ, Kiupel M, Rosenstein D, et al. Multipotential osteosarcoma with various mesenchymal differentiations in a young dog. Vet Pathol 2004; 41:264268.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5.

    Daffner R, Kennedy S, Fox K, et al. Synchronous multicentric osteosarcoma: the case for metastases. Skeletal Radiol 1997; 26:569578.

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