Multiple myeloma in a 9-year-old Labrador: Radiology perspective

Marie DeSwarte, DVM, DECVDI, DACVRObserving osteolytic lesions on radiographs is one of the four diagnostic criteria for multiple myeloma, so this modality plays an important role in the clinical work-up.1 Multiple myeloma usually involves multiple bone marrow sites in dogs and most commonly affects bones engaged in active hematopoiesis, such as the vertebrae, ribs, pelvis, skull, and proximal or distal long bones.1-4 Survey radiographs of the skeleton are recommended in suspected cases as a screening method for identification of bone lesions (Figure 8). Occasionally, these can appear on routine thoracic or abdominal radiographs as multiple discrete osteolytic (“punched out”) lesions, as subtler diffuse osteopenia or as both. Pathologic fractures may also occur.1,2,4 However, these radiographic changes are visible in only 25% to 30% of the dogs.1

The use of advanced imaging in cases of multiple myeloma has been scarcely reported in veterinary literature, but computed tomography (CT) and magnetic resonance imaging (MRI) could be superior to survey radiography in its detection.3 CT features of multiple myeloma are similar to the radiographic findings, including multiple punctate lucencies (poorly-marginated to well-demarcated) without evidence of periosteal reaction or sclerosis within the affected bones (Figure 9). Pathologic fractures may also be seen.3,5,6 On MRI, vertebral plasma cell tumors appear to be almost purely osteolytic, T1 isointense to hyperintense and T2 hyperintense to muscles (Figure 10). They variably but uniformly contrast-enhance.3,7

Figure 8. Lateral (a) and ventrodorsal (b) radiographs of the caudal abdomen of the patient at initial presentation. The radiographs show multifocal areas of moth-eaten lysis in the lumbar vertebral bodies (black circle). Multiple discrete osteolytic lesions are also present in the right femoral head and neck (dotted circle), as well as indistinct areas of osteolysis within the left femoral head and neck (white circle).

Figure 9. CT images of a plasma cell tumor in a 12-year-old mixed breed dog (not the patient in this case). Transverse (a) and multiplanar reformatted image in a parasagittal plane (b) of the thoracic spine in a bone window. Multifocal areas of lysis of the body and pedicles of the T5 vertebra without evidence of sclerosis are present (dotted circle). There is a pathologic fracture of the right pedicle at its junction with the lamina (arrow).

Figure 10. MRI images of a plasma cell tumor of T1 in an 11-year-old miniature schnauzer (not the patient in this case). Sagittal T2-weighted (a), T1-weighted (b) and STIR (c) images of the cervical and cranial thoracic spine. The vertebral body of T1 is diffusely hyperintense to muscles on T2-weighted, T1-weighted and STIR images (*). Note the hyperintense areas within the vertebral bodies of C7 and T2 on T2-weighted and T1-weighted images (arrows). These vertebrae are hypointense on STIR images, which indicates fat within the bone marrow and not neoplastic infiltration.Multiple myeloma has occasionally been reported to involve the spleen. Abdominal ultrasonography with ultrasound-guided sampling can be performed in case of splenomegaly detected by palpation or following abdominal radiographs. The sonographic changes attributed to multiple myeloma are multifocal, hypoechoic lesions. These changes are nonspecific and can be seen with other neoplastic processes such as lymphoma, histiocytic sarcoma and metastatic disease, as well as with benign processes such as nodular hyperplasia, extramedullary hematopoiesis, hematoma, infarcts and abscesses.8-10

Nuclear scintigraphy (bone scan) has been reported for clinical staging of dogs with multiple myeloma. However, this is an insensitive diagnostic method and is not recommended.1,11

References

Withrow S, Vail D, Page R. Myeloma-related disorders. In: Vail D, ed. Withrow and MacEwen's small animal clinical oncology. 5th ed. St. Louis: Elsevier, 2013.

Thrall DE. The canine and feline vertebrae. In: Textbook of veterinary diagnostic radiology. 6th ed. St. Louis: Elsevier, 2013.

Wisner E, Zwingenberger A. Vertebral column and spinal cord. In: Atlas of small animal CT and MRI. 1st ed. Ames: Wiley-Blackwell, 2015.

Maeda H, Ozaki K, Abe T, et al. Bone lesions of multiple myeloma in three dogs. Zentralbl Veterinarmed A 1993;40(5):384-392.

Schwarz T, Saunders J. Thoracic boundaries. In: Veterinary computed tomography. 1st ed. Chichester, UK Wiley-Blackwell, 2011.

Souchon F, Koch A, Sohns A. Multiple myeloma with significant multifocal osteolysis in a dog without a detectible gammopathy. Tierarztl Prax Ausg K Kleintiere Heimtiere 2013;41(6):413-420.

Petrovitch NP, Robertson ID, Mariani CL, et al. Relative T1 hyperintensity of solitary osseous vertebral plasmacytomas when compared to other vertebral tumors, in Proceedings. ACVR annual scientific meeting 2016.

Mattoon JS, Nyland TG. Spleen. In: Small animal diagnostic ultrasound. 3rd ed. St. Louis: Elsevier, 2015.

Day MJ, Penhale WJ, McKenna RP, et al. Two cases of IgA multiple myeloma in the dog. J Small Anim Pract 1987;28(2):147-156.

Geigy C, Riond B, Bley CR, et al. Multiple myeloma in a dog with multiple concurrent infectious diseases and persistent polyclonal gammopathy. Vet Clin Pathol 2013;42(1):47-54.

Daniel GB, Berry CR. Small animal skeletal scintigraphy. In: Textbook of veterinary nuclear medicine. 2nd ed. Harrisburg, Pennsylvania: American College of Veterinary Radiology, 2006.