History
fig. 1 - lateral radiograph of lumbar spine. There is extensive, bridging spondylosis of ventral spine with evidence of loss of mineralisation within the L7-S1 bridging bone ventrally, but the corresponding vertebral body end-plates appear intact.
fig. 2 - ventrodorsal radiograph showing moderate degenerative changes to the hips
A three-year-old male, neutered, Basset Hound presented to the referring veterinary surgeon with a history of spinal pain and pelvic limb weakness. Signs were first noted one week previously as sudden onset exercise intolerance with concurrent loss of appetite. There was an initial, partial response to meloxicam 2.5mg q24h P.O. and diazepam 2mg q8h P.O. However, over the course of the following week signs worsened again; by the morning of presentation, the left pelvic limb was non-weight bearing lame.
On clinical examination, the patient was able to stand and walk slowly, but subdued and reluctant to move. There was generalised inflammation of the skin which emitted a characteristic ‘yeasty’ odour. Mild, generalised lymphadenopathy was noted. There was resentment to palpation and manipulation of the caudal lumbar spine lateralised to the left. Neurological examination revealed slightly delayed conscious proprioceptive testing in the left pelvic limb with normal segmental spinal reflexes. Routine biochemistry was unremarkable. Haematology revealed a mild neutrophilia 12.27(2-12)x109/l and monocytosis 2.56(0.3-2)x109/l.
Imaging
fig. 3 - sagittal T2W slice of caudal lumbar spine showing inflammatory pattern within bridging spondylosis ventral to the L7-S1 disc, which, although degenerate, does not appear inflamed itself.
Radiology was performed under general anaesthesia which revealed marked, ventral spondylosis extending from the sacrum as far cranially as T12. Orthogonal views revealed degenerative changes to both hips (figs. 1 & 2). MRI scans of the lumbar spine (figs. 3 & 4) revealed a focal area of increased signal intensity on T2W in the area of demineralising bone within the spondylosis ventral to L7-S1.
Corresponding T1W sequences yielded a low signal intensity with post-gadolinium contrast ring-enhancement, consistent with infection/inflammation. In addition, there was a focal area of high signal on STIR sequences within the neural canal on the left side consistent with empyema (fig. 5). With both the T2W and STIR sequences, the L7-S1 intervertebral disc itself did not appear grossly affected other than a slight increase in signal within the right, lateral annulus. In addition to the changes to the spine noted above, there was a diffuse, patchy ‘irritation pattern’, indicative of cellulitis of the paraspinal soft tissues surrounding the lumbosacral region (fig. 6).
fig. 4 - T2W transverse slice through L7-S1 disc, showing inflammatory signal beneath disc.
Blood culture yielded a heavy, pure growth of Staphylococcus aureus, sensitive to a broad spectrum of antibiotics including both cefuroxime and marbofloxacin. Urine cultures and serology for Brucella canis were both found to be negative.
Initial therapy with metronidazole 250mg q12h I.V. and cefuroxime 625mg q12h I.V. was instituted, pending bacteriology results. Analgesia was provided using a combination of lidocaine 20 ug/kg/min I.V. and ketamine 5ug/kg/min I.V. as a constant rate infusion. In addition, meloxicam 2.5mg q24h P.O., methadone 6mg q8h I.M. and gabapentin 200mg q12h P.O. were used to control pain.
Although there was initial improvement in clinical signs, nerve root signature subsequently developed in the right pelvic limb, which failed to respond to the addition of marbofloxacin 50mg q24h I.V. to the above regime.
Further investigations and treatment, including surgical biopsy, foraminal decompression, debridement, lavage and omentalisation were discussed. However, the owner elected not to pursue treatment and the dog was euthanased.
Discussion:
fig. 5 - STIR sagittal slice showing area of high signal within the neural canal, dorsal to the L7-S1 disc.
Spondylosis
may be defined as ankylosis of a vertebral joint and is used to describe degenerative changes of the spinal column. It is a common, often incidental radiographic finding in the aging canine population.
Spondylitis may be defined as active infection of the vertebral bone (osteomyelitis), including any associated periarticular new bone e.g. bridging spondylosis.
Discospondylitis describes the destructive inflammatory and proliferative process involving the intervertebral discs, their associated endplates and by extension, the vertebral bodies1.
This case illustrates an unusual situation, where there is significant inflammation of the surrounding bone and soft tissues, yet the disc itself appears unaffected. This phenomenon has been reported in the human literature, where paraspinal abscesses and/ or septic spondylitis have been described. To our knowledge, there are no reports of MRI findings with septic spondylosis in the absence of associated discospondylitis in the veterinary literature.
References:
fig. 6 - STIR dorsal slice showing diffuse patchy increased signal consistent with cellulitis around the lumbar spine.
1.Carrera I et al (2010) MRI features of discospondylitis in dogs. Vet Radiol & Ultrasound in press
2.Cherubini GB et al (2004) MRI findings in a dog with discospondylitis caused by Bordetella species. JSAP 45:417-20
3.Forrester DM (2004) Infectious spondylitis. Semin Ultrasound CT MR. 25:461-73
4.Gonzalo-Orden JM et al (2000) MR, CT and radiologic findings in a dog with discospondylitis. Vet Radiol & Ultrasound 41:142-4
5.Holloway A et al (2009) MRI features of paraspinal infection in the dog and cat. Vet Radiol & Ultrasound 50:285-91
6.Stefani de A et al (2008) MRI features of spinal epidural empyema in five dogs. Vet Radiol & Ultrasound 49:135-40
7.Tali ET (2004) Spinal infections. Eur J Radiol 50:120-33
8.Thrush A; Enzmann D (1990) MR imaging of infectious spondylitis. A J Neuroradiology 11:1171-80
9. Vorbeck F et al (1996) Infectious spondylitis in adults. Radiologe 36:795-804
