Abstract
In collaboration with the American College of Veterinary Radiology
History
An approximately 2-year-old 23.6-kg spayed female mixed-breed dog was evaluated for chronic, intermittent difficulty with stairs and when rising. The owners reported that they had adopted the dog from an animal rescue organization 5 months earlier, they were told at that time that the dog had a shoulder joint problem and that the dog had exhibited intermittent signs of pain since adoption.
On physical examination, the dog was bright, alert, and responsive but seemed fearful and would not allow a full physical examination. The dog had a clinically normal range of motion in the forelimbs and neck without signs of pain but consistent signs of pain with palpation along the thoracolumbar portion of the vertebral column and would not allow assessment of the hind limbs or abdomen. The dog was returned to the clinic 2 days later for sedation and radiography of the vertebral column (Figure 1).
Right lateral (A) and ventrodorsal (B) radiographic images of the thoracolumbar region of the vertebral column of a 2-year-old 23.6-kg spayed female mixed-breed dog evaluated for chronic intermittent difficulty on stairs and when rising. The images are published with permission by Dr. Jeffrey Schulman, the copyright holder with all rights reserved. Anyone wishing to reproduce the images is directed to contact Dr. Schulman at the Kenwood Pet Clinic, 2107 Penn Ave South, Minneapolis, MN 55405.
Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.20.02.0088
Formulate differential diagnoses, then continue reading.
Diagnostic Imaging Findings and Interpretation
Radiography revealed multifocal vertebral endplate lysis, irregular endplate margins between T11 and L4, and 1 narrowed intervertebral disk space at T13 to L1 (Figure 2). Endplate lysis was focal for T11 to T12 and L1 to L2, and multifocal between T12 and L1 and for L2 to L4. The intervertebral disk space at T13 to L1 was narrowed dorsally with a widened appearance ventrally due to endplate lysis. The intervertebral foramen at this site had decreased size, compared to adjacent foramina, suggestive of disk bulging, herniation, or both. The lengths of the vertebral bodies of T13 and L1 were foreshortened secondary to the lysis at both the cranial and caudal margins. Sclerosis was present in the vertebral bodies adjacent to most of these lytic areas but was especially prominent for T13, L1, and L3 to L4. Spondylosis deformans with varying amounts of intervertebral bone proliferation and bridging across the ventral disk spaces were identified for T12 to L1 and L3 to L4. Disk spaces from L4 to S1 had clinically normal widths and no evidence of lysis.
The same images as in Figure 1. Between T11 and L4, there are focal (black arrowheads) and multifocal (white arrowheads) areas of vertebral endplate lysis, irregular endplate margins, and spondylosis deformans (black arrows) with varying amounts of intervertebral bone proliferation and bridging. Sclerosis is present adjacent to most areas of endplate lysis, of these lytic areas. The T13 to L1 intervertebral disk space is narrowed dorsally and has a widened appearance ventrally due to endplate lysis, and the intervertebral foramen at this site has decreased size, compared to adjacent foramina, suggestive of disk bulging, herniation, or both. The images are published with permission by Dr. Jeffrey Schulman, the copyright holder with all rights reserved. Anyone wishing to reproduce the images is directed to contact Dr. Schulman at the Kenwood Pet Clinic, 2107 Penn Ave South, Minneapolis, MN 55405.
Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.20.02.0088
On the basis of the radiographic findings, a diagnosis of multifocal discospondylitis and probable osteomyelitis of T13 was made. Primary differential diagnoses were bacterial infection (eg, Staphylococcus spp, Streptococcus canis, Escherichia coli, or Brucella canis) or fungal infection (eg, Aspergillus, Fusarium, or Paecilomyces spp); given the dog’s young age and lesion location in the disk spaces, neoplasia was considered unlikely. A CBC, serum biochemical analysis, urinalysis, and bacterial cultures on samples of urine and blood were performed to identify a causative agent. Given her sexually mature age and history as a stray when rescued, B canis serology was also performed. The CBC revealed a mild monocytopenia (150 monocytes/µL; reference range, 200 to 1,500 monocytes/µL) and severe eosinophilia (14,800 eosinophils/µL; reference range, 0 to 800 eosinophils/µL). No abnormalities were detected on serum biochemical profile or urinalysis, and the bacterial culture performed on urine yielded no growth.
Serologic testing was performed at a reference laboratory by the screening rapid slide agglutination test (RSAT), and the results were positive. The second-tier agar gel immunodiffusion (AGID-II) confirmatory assay was then performed, and results were negative, making serology results inconclusive. Serologic tests have variable sensitivity and specificity for B. canis, infected dogs may initially test negative, antibody titers can fluctuate even if bacteremia is persistent, chronically infected dogs may also test seronegative, and the tests generally perform best during early stages of infection.1–3
One of 2 blood samples submitted for bacterial culture grew a gram-negative bacillus after 5 days that was identified as B canis by the National Veterinary Services Laboratory in Ames, Iowa. On the basis of the positive blood culture, the final diagnosis was discospondylitis caused by B canis.
Treatment and Outcome
Treatment of canine brucellosis with antimicrobials is not recommended.1–3 As an intracellular bacteria, B canis can hide from the immune system, cause intermittent bacteremia and recrudescence of infection, and no antimicrobial is 100% successful in eliminating the bacteria. The bacteria are shed in nonestrus vaginal secretions, semen, blood, saliva, nasal secretions, and urine. Spayed or castrated dogs that have B canis are still a risk for human exposure because the bacteria can continue to be shed in urine.1 A permanent home quarantine for the dog was issued by the state’s animal health authority due to this zoonotic potential, after which the owners elected euthanasia for the dog, followed by necropsy.
Necropsy was conducted at a biosafety level-3 (BSL-3) veterinary diagnostic laboratory. On gross examination, the spleen had a well-demarcated, white, raised, soft nodule (1.6 X 1.2 X 1 cm). On the cut section, the intervertebral disks and the endplates of multiple vertebral bodies of the thoracolumbar region had well-demarcated dark red foci, up to 2 mm in diameter. Histopathology of the affected sites revealed that the vertebral bone in these foci was replaced by strands of fibrous connective tissue with dense infiltrates of plasma cells. The splenic nodule was composed of lymphocytes and plasma cells and interpreted to have been nodular lymphoid hyperplasia. Bacterial cultures performed at a BSL-3 laboratory isolated bacterium from spleen and a retropharyngeal lymph node. Based on results of the PCR assay performed at the CDC, the isolated organism was identified as B canis. Samples of urine, liver, kidney, bone marrow, and lung as well as swab specimens of the T13 to L1 disk, right stifle joint, and vagina tested negative for Brucella. Despite a positive culture in lymph node and spleen, these tissues did not have any meaningful gross or histologic lesions. In contrast, the only meaningful Brucella-associated lesion in the vertebral column was negative for this pathogen.
Comments
Discospondylitis is an infection of the intervertebral disk and adjacent vertebral bodies. It may occur as unifocal or multifocal lesions in 1 or several nonadjacent vertebrae and is more common in the thoracic or lumbar portion of the vertebral column.1,2 It may result in extradural spinal cord compression, narrowed intervertebral disk space, lysis of the vertebral endplates, sclerosis adjacent to lytic lesions, spondylosis deformans, and poorly localized pain.1,4 Clinical signs depend on the location of the affected vertebrae and chronicity of the infection. They may include pain or hyperesthesia over involved sites, lameness, and mild to severe neurologic deficits.
A blood culture is the best method for early detection of disease, but negative results do not rule out infection because B canis may exhibit episodic bacteremia.1–3 The RSAT is highly sensitive and a good screening test for early infections, whereas the AGID test is highly specific and useful as a confirmation test but may yield negative results early in an infection.1 The negative results for bacterial culture from the vertebral column in the dog of the present report may have reflected different sampling techniques used, because a swab was used to sample the intervertebral disk, whereas tissue samples were collected from the spleen and lymph node.
Survey radiographic examination of the vertebral column was a key diagnostic tool used to identify the discospondylitis that led to the diagnosis of infection of B canis. With the possibility of multifocal lesions and poorly localized pain in discospondylitis, it is important to perform survey radiography of the full vertebral column. However, there may be a delay in developing radiographic signs; thus, normal radiographic findings do not rule out this condition.4 Repeat radiography in several days to weeks or advanced imaging (MRI or CT) may also be needed to ensure an accurate diagnosis. Because populations of feral and stray dogs are more likely to be intact and serve as reservoirs for B. canis, thorough diagnostic efforts are critical to minimize the risk of human exposure.3,5
References
- 1. ↑
Kauffman LK, Peterson CA. Canine brucellosis, old foe and reemerging scourge. Vet Clin North Am Small Animal Pract. 2019;49(4):763–779.
- 2. ↑
Makloski CL. Canine brucellosis management. Vet Clin North Am Small Animal Pract. 2011;41(6):1209–1219.
- 3. ↑
Hensel ME, Negron M, Arenas-Gamboa AM. Brucellosis in dogs and public health risk. Emerg Infect Dis. 2018;24(8):1401–1406.
- 4. ↑
Ruoff CM, Kerwin SC, Taylor AR. Diagnostic imaging of discospondylitis. Vet Clin North Am Small Anim Pract. 2018;48(1):85–94.
- 5. ↑
Simmons KE, Hoffman CL. Dogs on the move: factors mapping animal shelter and rescue organizations’ decisions to accept dogs from distant locations. Animals (Basel). 2016;6(2):11.
