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Maris Terpstra Rainbow Equine Hospital, Malton, YO17 6SG, England.

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Sarah Gough Rainbow Equine Hospital, Malton, YO17 6SG, England.

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Jonathon J. Dixon Rainbow Equine Hospital, Malton, YO17 6SG, England.

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History

A 9-year-old approximately 450-kg (990-lb) Welsh Cob section D gelding was referred following identification of severe lameness in the right forelimb. The gelding had been variably lame for approximately 7 weeks, with some improvement with stall rest and oral administration of phenylbutazone (2.2 mg/kg [1.0 mg/lb], PO, q 12 h for 5 days); however, shortly before referral, the gelding's lameness had consistently been a grade 4/5. On presentation, the gelding was bright and alert and had a heart rate of 44 beats/min (reference range, 28 to 44 beats/min), respiratory rate of 16 breaths/min (reference range, 8 to 12 breaths/min), and rectal temperature of 37.9°C (100.2°F; reference range, 37.2°C to 38.3°C [99°F to 101°F]). The gelding had right forelimb lameness (grade 4/5) at a walk. Palpation of the shoulder joint region elicited signs of substantial discomfort; however, flexion and extension of the limb did not worsen the lameness. On the basis of repeatable signs of substantial discomfort during palpation of the proximal aspect of the humerus and the surrounding soft tissues, radiography was performed (Figure 1).

Figure 1—
Figure 1—

Mediolateral (A) and slightly craniomedial-caudolateral oblique (B) radiographic images of the right shoulder joint of a 9-year-old approximately 450-kg (990-lb) Welsh Cob section D gelding with severe lameness (grade 4/5) in the right forelimb and signs of pain on palpation of the shoulder joint. In both images, the gelding's head is toward the left; images were obtained with a digital radiographic system set at 85 kVp and 36 mAs with a 1-m focal distance.

Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.907

Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →

Diagnostic Imaging Findings and Interpretation

Radiography revealed a large (approx 6.9 × 6.1-cm) rounded osteolytic region in the caudoproximal aspect of the right humerus (Figure 2). The lesion extended from the proximal portion of the diaphysis into the proximal metaphysis and epiphysis. The most distal portion of the lesion had ill-defined margins and a poorly differentiated zone of transition to normal trabecular bone. Caudal to the lesion, cortical bone of the neck of the humerus appeared thickened and had areas of lysis, and distal to this, a well-defined and smoothly outlined area of periosteal reaction was evident for a length of 3.4 cm along the caudal margin of the humeral metaphysis. In addition, a distinct, thin radiolucent line extended from the caudodistal margin of the large, round lytic lesion and coursed craniodistally into the diaphysis of the humerus, consistent with a fracture. No radiographic abnormalities were evident in the right scapula or shoulder joint.

Figure 2—
Figure 2—

Same images as in Figure 1. A large (approx 6.9 × 6.1-cm) rounded area of greater radiolucency with poorly defined distal margins, consistent with an osteolytic lesion (black arrows), is evident in the proximal aspect of the humerus. Caudally, there is a region of cortical bone lysis (arrowheads) with a distally adjacent region of periosteal reaction. A distinct, thin radiolucent line (white arrows) extends from the caudodistal margin of the large round lytic lesion and courses craniodistally into the diaphysis of the humerus, consistent with a fracture.

Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.907

The radiographic findings suggested a monostotic aggressive bone lesion and pathological fracture in the proximal aspect of the humerus, without involvement of the shoulder joint. The most likely differential diagnosis was neoplasia with a secondary pathological fracture. Another differential diagnosis, but less likely, was osteomyelitis.

Treatment and Outcome

Aseptic arthrocentesis of the right shoulder joint was performed, and cytologic examination of a synovial fluid sample revealed a total protein concentration of 60 g/L (reference limit, ≤ 20 g/L) and a WBC count of 2.7 × 109 WBCs/L (reference limit, ≤ 5 × 109 WBCs/L). These results suggested synovial sepsis was unlikely. Radiographic examination of the thorax was performed (not shown) to assess for the presence of metastatic lesions; none were observed. Because of the combination of no appropriate fracture-fixation option and the gelding's grave prognosis and clinical signs of discomfort, euthanasia was recommended. The owners agreed.

Postmortem examination confirmed the osteolytic lesion and fracture identified radiographically; however, the fracture was more extensive than appreciated antemortem, in that fracture propagation had spiraled in several planes through the length of the right humeral diaphysis and was considered a complete, non-displaced diaphyseal fracture (Figure 3).

Figure 3—
Figure 3—

Mediolateral (A) and craniocaudal (B) postmortem radiographic images of the disarticulated humerus described in the previous figures with the soft tissues removed. The extents of a large osteolytic lesion (black arrows), cortical defect (gray arrow; B), and fracture (white arrows) are more clearly evident here, compared with the antemortem radiographic images, and the number and extent of fracture planes identified exceed those appreciated antemortem.

Citation: Journal of the American Veterinary Medical Association 257, 9; 10.2460/javma.257.9.907

Results of histologic examination of bone sections from the affected humerus indicated a poorly differentiated sarcoma of mesenchymal origin. Despite extensive additional investigation with immunohistochemistry, further distinction was not possible.

Comments

Antemortem radiographic examination of the shoulder joint in the gelding of the present report was performed with the horse in a standing position and with the affected limb elevated and pulled forward and slightly distally.1 Our initial findings suggested a monostotic aggressive bone lesion in the proximal aspect of the humerus, not extending into the shoulder joint, and postmortem findings confirmed this.

Although primary bone neoplasia in horses is rare, the hallmark radiographic features of aggressive bone lesions are similar to those in other species, including loss of integrity of cortical bone, active (irregular) periosteal bone formation, and a long, poorly defined zone of transition within the bone.2 Nuclear scintigraphy or CT may be used to evaluate the extent of bone destruction and locate metastases.3 In the gelding of the present report, CT could not be used because of the anatomic area of interest. General anesthesia would have been required; however, because a fracture line had been identified on radiography, general anesthesia for the gelding without the possibility of fracture repair would have been contra-indicated.

The differential diagnoses for a lesion with the radiographic abnormalities identified in the horse of the present report were neoplasia and osteomyelitis. Involvement of the shoulder joint was unlikely on the basis of radiographic findings. In addition, results of cytologic examination of synovial fluid obtained by arthrocentesis of the right shoulder joint ruled out synovial sepsis and suggested that osteomyelitis may have been less likely. Biopsy of the affected humerus was discussed with the owner as part of the diagnostic plan; however, because of the clinical and radiographic findings and grave prognosis for the gelding, it was believed that the outcome of histologic examination of such a biopsy sample would not alter the treatment or outcome for the gelding. Thus, for humane reasons, euthanasia was elected. Radiographic examination was crucial for providing an accurate and prompt diagnosis of the underlying cause of lameness and prognosis for the gelding in the present report.

References

  • 1. Redding WR, Pease AP. Imaging of the shoulder. Equine Vet Educ 2010;22:199209.

  • 2. Thrall DE. Introduction to radiographic interpretation. In: Textbook of veterinary diagnostic radiology. 6th ed. St Louis: Elsevier, 2013;85–86.

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  • 3. Vanel M, Blond L, Vanel D. Imaging of primary bone tumors in veterinary medicine: which differences? Eur J Radiol 2013;82:21292139.

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