Computed tomographic findings in dogs with multiple myeloma.

Background: Computed tomography (CT) is considered the first-line imaging modality for human patients with suspected multiple myeloma (MM). Recently the diagnostic criteria for human MM have been updated.

Objectives: To describe and provide a baseline of the CT features and distribution of osseous lesions in dogs diagnosed with MM and to describe the change of initial osseous lesions after the start of treatment in a subset of dogs.

Methods: Single-centre, retrospective, descriptive, case series. Dogs were included when they met the updated MM criteria and if a staging CT was performed at the time of diagnosis and prior to initiation of treatment. When available, change of osseous lesions was assessed on serial imaging studies.

Results: Thirteen dogs met the inclusion criteria. All dogs had involvement of the axial skeleton and 9/13 (69%) had concurrent involvement of the appendicular skeleton. Large (≥1 cm), lytic, 'punched out' or expansile bony lesions and regions of permeative lysis were most common and mainly affected the vertebral column. Discrete intramedullary soft tissue attenuating lesions of the proximal appendicular skeleton were observed in 8/13 dogs (61%) and bilateral involvement of both humeri and femurs was seen in 4/9 dogs (44%). A subset of dogs underwent serial imaging and progressive replacement of the contrast-enhancing lesions with fat attenuating tissue was observed for all dogs, corresponding with clinical improvement.

Conclusions: This case series provides a baseline knowledge of the initial and follow-up CT features in dogs diagnosed with MM based on updated criteria.