Assessment Anatomic diagnosis

Etiologic diagnosis—Differential diagnoses included degenerative disease (recurrence of clinical signs secondary to compression at previous or new site of intervertebral disk herniation), infectious or inflammatory disease (diskospondylitis or meningitis), and neoplasia (primary or metastatic). The diagnostic plan included urinalysis with culture of a urine sample, CBC, serum biochemical analysis, thoracic radiography (to assess for metastatic disease), cervical radiography (to assess for diskospondylitis or neoplastic lesions), abdominal ultrasonography (to evaluate for primary neoplasia and source of hematuria), MRI with and without IV administration of contrast medium,^b and CSF specimen analysis (if warranted on the basis of MRI imaging results).

Diagnostic test findings—The CBC revealed a mild inflammatory leukogram, characterized by normal WBC count with neutrophilia (11,920 neutrophils/μL; reference interval, 2,060 to 10,600 neutrophils/μL) and monocytosis (1,341 monocytes/μL; reference interval, 0 to 840 monocytes/μL). Serum biochemical results were considered unremarkable. Urinalysis revealed pyuria (WBC count, 21 to 50 cells/hpf [40×])> and bacteriuria (> 100 rods/hpf). Culture of a urine sample yielded heavy growth of Escherichia coli. There was no evidence of metastatic disease on thoracic radiographs. Cervical radiography revealed multiple narrowed disk spaces with associated spondylosis, most consistent with chronic intervertebral disk disease. Abdominal ultrasonographic findings included a moderate amount of echogenic debris within the urinary bladder and a 1 × 2-cm hypoechoic splenic mass. Fine-needle aspirate specimens of the splenic mass were collected for cytologic examination, the results of which were consistent with lymphoid hyperplasia. Magnetic resonance imaging was performed 1 week after the initial evaluation of the dog to allow for patient stabilization and return of the cytologic examination results. On the MRI images, there was T2-weighted hyperintensity and increased STIR signal (compared with surrounding parenchyma) centered at the C4-5 intervertebral disk space and extending into the vertebral endplates. This site was hypointense on T1-weighted images and enhanced following contrast medium administration (Figure 1). A well-defined, fusiform, contrast-enhancing lesion was present within the ventral aspect of the vertebral canal at this location and caused dorsal displacement and flattening of the spinal cord. From the level of C3-C6, the hypaxial and paraspinal musculature contained high T2-weighted signal changes with contrast enhancement. Imaging findings were considered consistent with diskospondylitis, empyema, and associated myositis.

Sagittal (A and C) and transverse (B and D) T1-weighted images of the cervical portion of the vertebral column of a 13-year-old Maltese before (A and B) and after (C and D) IV injection of contrast medium. The dog was evaluated because of a sudden onset of tetraparesis and signs of cervical pain 24 hours earlier. Notice the area of hypointensity at the C4-5 intervertebral disk space and corresponding vertebral endplates (A and B). Following contrast administration, there is enhancement of the soft tissue structures surrounding the C4-5 disk space, and a fusiform mass lesion is evident in the ventral epidural space (C and D).

Citation: Journal of the American Veterinary Medical Association 257, 12; 10.2460/javma.257.12.1231

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Sagittal (A and C) and transverse (B and D) T1-weighted images of the cervical portion of the vertebral column of a 13-year-old Maltese before (A and B) and after (C and D) IV injection of contrast medium. The dog was evaluated because of a sudden onset of tetraparesis and signs of cervical pain 24 hours earlier. Notice the area of hypointensity at the C4-5 intervertebral disk space and corresponding vertebral endplates (A and B). Following contrast administration, there is enhancement of the soft tissue structures surrounding the C4-5 disk space, and a fusiform mass lesion is evident in the ventral epidural space (C and D).

Citation: Journal of the American Veterinary Medical Association 257, 12; 10.2460/javma.257.12.1231

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Sagittal (A and C) and transverse (B and D) T1-weighted images of the cervical portion of the vertebral column of a 13-year-old Maltese before (A and B) and after (C and D) IV injection of contrast medium. The dog was evaluated because of a sudden onset of tetraparesis and signs of cervical pain 24 hours earlier. Notice the area of hypointensity at the C4-5 intervertebral disk space and corresponding vertebral endplates (A and B). Following contrast administration, there is enhancement of the soft tissue structures surrounding the C4-5 disk space, and a fusiform mass lesion is evident in the ventral epidural space (C and D).

Citation: Journal of the American Veterinary Medical Association 257, 12; 10.2460/javma.257.12.1231

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Comments

Spinal epidural empyema, a focal collection of purulent material within the epidural space of the vertebral canal, is an uncommon disease in dogs.¹ It is considered a surgical emergency in human medicine because of the associated morbidity and risk of death in the absence of prompt treatment. Clinical signs can range from signs of spinal pain to severe neurologic dysfunction. An inflammatory leukogram and fever may be present. A compressive lesion can be detected with myelography, but the imaging technique of choice is MRI. The MRI features of empyema are a T2-weighted hyperintense mass lesion causing extradural cord compression that has either peripheral or diffuse contrast enhancement. A gradient echo signal void and abnormal intramedullary signal may also be seen.² Fortunately, the prognosis for dogs with empyema is good following treatment. The current published recommendation for dogs with empyema is surgical decompression, debridement, and antimicrobial administration (determined on the basis of the results of culture and antimicrobial susceptibility testing).^1,3 There have also been cases of improvement of affected dogs with medical intervention alone.⁴

Empyema has been reported to develop in conjunction with diskospondylitis, which is defined as an infection of the vertebral endplates with secondary invasion of the intervertebral disk.⁵ Dogs with diskospondylitis also have a good prognosis with treatment, although surgery is not initially indicated unless instability or pathological fracture of the vertebral column is present. Treatment should include antimicrobial administration and exercise restriction, and pain medication when needed. A diagnosis of diskospondylitis can be made radiographically, but MRI is helpful in acute cases because radiographic changes can lag 2 to 4 weeks behind the development of clinical signs. Moreover, MRI provides additional information regarding potential comorbidities (eg, meningitis or myelitis) in patients with severe neurologic deficits. The MRI findings associated with diskospondylitis are hyperintensity of the vertebral endplates on T2-weighted images, hyperintensity of at least 1 intervertebral disk space on T2-weighted and STIR images, paravertebral hyperintensity, and heterogeneous contrast enhancement of the endplates and intervertebral disk space.⁶ All of these were imaging features evident in the case described in the present report.

The diagnosis of diskospondylitis and empyema in the dog of the present report was unique in that the dog did not have the signalment or lesion localization that is generally associated with these diseases in dogs. Among dogs, diskospondylitis most commonly develops at any age in large breeds (dogs weighing > 25 kg [> 55 lb]), males, and purebreds.^1,5,6 The most commonly affected site is L7-S1.⁵ Cervical lesions have been noted in only 17 of 123 (13.8%) dogs in 1 study,⁵ and only 3 of 56 affected disk spaces were in the cervical region in another 23 dogs.⁶ Empyema is also primarily reported as affecting large-breed dogs and is most commonly localized to the thoracic and lumbar portions of the vertebral column.^2,3

The suspected source of infection in the dog of the present report was hematogenous spread of a urinary tract infection. It was postulated that prior intervertebral disk disease with associated instability and degenerative bony changes of the vertebral column predisposed the dog to infection at this location. Pathological mechanisms that can contribute to development of diskospondylitis include microfractures, alterations in blood flow, and focal endplate necrosis.⁵ Urinary tract infection is considered the most common nidus of diskospondylitis, but other potential sources include dental disease, endocarditis, respiratory tract infection, abscesses, and open wounds.⁵

Microbial culture of blood and urine samples is recommended in cases of diskospondylitis to guide antimicrobial treatment, although a causative agent may not be identified. Empirical treatment can be started with a cephalosporin (with or without a fluoroquinolone) because the most commonly identified organisms are coagulase-positive Staphylococcus spp, Streptococcus spp, and E coli.¹ Duration of treatment is based on clinical signs and resolution of radiographic changes. For dogs with diskospondylitis, antimicrobial treatment should be continued for at least 8 weeks,¹ although the mean reported treatment period in 1 study⁵ was 53.7 weeks.

With regard to the dog of the present report, the client declined surgical debridement of the empyema. Oral treatment of the dog with marbofloxacin was instituted on the basis of antimicrobial susceptibility data derived from testing of the organisms isolated following culture of a urine sample. Because of empyema, clindamycin was added for expanded antimicrobial coverage of anaerobic and gram-positive organisms and because high concentrations of the drug can be attained in bone and tissues. Seven days after starting antimicrobial treatment, the dog's condition had improved and it was ambulatory with mild tetraparesis. The dog was rechecked again 28 days after initial diagnosis, and it was ambulatory without paresis or other deficits. Fifty-three days after diagnosis, the dog had returned to a normal energy level (as reported by the owner); its body weight had increased by 20%, and there had not been any reported recurrence of lower urinary tract signs.