What Is Your Diagnosis?

Wendi Velando Rankin Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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Carolyn J. Henry Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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David A. Kunz Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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Fred Williams III Veterinary Medical Diagnostic Laboratory, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.

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History

An 11-year-old spayed female Rottweiler was evaluated for progressive lameness of the right forelimb of 8 weeks' duration; the limb was non–weight-bearing for 4 weeks' duration. The dog was housed outdoors only, its vaccination status was not adequate, and it did not receive heartworm preventative.

Abnormalities detected during physical examination included a non–weight-bearing lameness of the right forelimb and a firm swelling (approx 13 × 10 × 10 cm) extending from the distal third of the humerus to the proximal aspects of the radius and ulna. Flexion of the elbow joint elicited signs of pain. Results of a CBC indicated normocytic, normochromic anemia (Hct, 30%; reference range, 37% to 55%); microfilaria were observed in the blood smear. Abnormalities detected on plasma biochemical analysis included hypoalbuminemia (2.1 g/dL; reference range, 2.9 to 4 g/dL) and hyperglobulinemia (4.6 g/dL; reference range, 2.2 to 3.6 g/dL). No abnormalities were detected on urinalysis or radiographs of the thorax. Radiographs of the right elbow joint were obtained (Figure 1).

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

Figure 1—
Figure 1—

Lateral (A) and craniocaudal (B) radiographic views of the right elbow joint of an 11-year-old spayed female Rottweiler evaluated for lameness of the right forelimb of approximately 8 weeks' duration.

Citation: Journal of the American Veterinary Medical Association 229, 6; 10.2460/javma.229.6.929

Radiographic Findings and Interpretation

A moderate amount of soft tissue swelling surrounding the distal aspect of the humerus and elbow joint and a marked, irregular periosteal reaction from the mid-diaphysis of the humerus to the elbow joint can be seen (Figure 2). An amorphous periosteal reaction surrounds the olecranon.

Figure 2—
Figure 2—

Same radiographic views as in Figure 1. Notice the periosteal reaction on the humerus and across the elbow joint on the olecranon (arrows).

Citation: Journal of the American Veterinary Medical Association 229, 6; 10.2460/javma.229.6.929

Because of the polyostotic lesion, differential diagnoses included metastatic neoplasia (carcinoma) or primary bone tumors of vascular or hemolymphatic origin (lymphoma, hemangiosarcoma, or multiple myeloma). Because the lesion crossed the joint, synovial cell sarcoma was also considered as a differential diagnosis. Other primary bone tumors including osteosarcoma, chondrosarcoma, and fibrosarcoma, as well as fungal osteomyelitis, were considered less likely.

Comments

Further diagnostic testing and treatment were offered to the owners, including abdominal ultrasonography to check for metastatic or primary disease, nuclear scintigraphy, computed tomography to determine the extent of the bone lesion, an aspirate or biopsy of the lesion, amputation of the limb, and treatment for heartworm disease. However, the dog was euthanatized because of financial limitations.

Necropsy revealed that the right forelimb mass extended from the distal diaphysis of the humerus to the proximal diaphyses of the radius and ulna. The right axillary lymph node was large, and several masses (2 to 4 mm in diameter) were detected in both renal cortices. Dirofilaria immitus were detected in the right ventricle. Histologic examination of the forelimb mass revealed polygonal cells with frequent mitoses (90 mitoses/10 hpf at 400X magnification) and tumor cells invading cortical bone and underlying marrow. Similar neoplastic cells effaced the right axillary lymph node and renal cortices. Results of immunohistochemistry indicated that tumor cells were positive for the lambda light chain immunoglobulin. These characteristics were compatible with multiple myeloma.

Multiple myeloma classically involves bones such as the vertebrae, ribs, pelvis, skull, and proximal or distal aspects of long bones in which hematopoiesis is greatest.1 Although the lesion involved a long bone, findings in this dog were unusual because multiple myeloma lesions are typically characterized by osteolysis or osteoporosis.1–3 The classic radiographic appearance of bone lesions in animals with multiple myeloma includes punched-out areas of lyis.1 Myeloma cells release osteoclastic activating factor, or receptor of NF-kB ligand, which causes lysis of bone, with little or no bone formation.4 However, the dog in this report had a primarily proliferative lesion, indicating the importance of including plasmacytoma or multiple myeloma as differential diagnoses for proliferative bone lesions.

A diagnosis of multiple myeloma is usually made by cytologic analysis of a bone marrow aspirate.1 A bone marrow core biopsy may be necessary, as plasma cells can cluster in bone marrow, preventing a definitive diagnosis with an aspirate.1 In the dog of this report, the extensive amount of bone proliferation in the tumor may have prevented obtaining a diagnostic sample with a simple fine-needle aspirate of the lesion, in which case a biopsy of the bone lesion or bone marrow core biopsy at the site would have been required.

  • 1

    Withrow SJ, MacEwen EG. Small animal clinical oncology. 3rd ed.Philadelphia: WB Saunders Co, 2001;378–417, 626–638.

  • 2

    Matus RE, Leifer CE, MacEwen EG, et al. Prognostic factors for multiple myeloma in the dog. J Am Vet Med Assoc 1986;188:12881292.

  • 3

    Morgan JP. Systematic radiographic interpretation of skeletal diseases in small animals. Vet Clin North Am Small Anim Pract 1974;4:611626.

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  • 4

    MacEwen EG, Patnaik AK, Hurvitz AI, et al. Nonsecretory multiple myeloma in two dogs. J Am Vet Med Assoc 1984;184:12831286.

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