Acute Thoracolumbar IVD Extrusion. Tracy Sutton, DVM, DACVIM (Neurology)

Transcription

1 Acute Thoracolumbar IVD Extrusion Tracy Sutton, DVM, DACVIM (Neurology)

2 CONTACT INFORMATION Austin Veterinary Emergency Specialty Center (AVES) 7300 Ranch Road 2222, Austin, TX (512)

3 Outline Pathophysiology Incidence Clinical signs Differential diagnoses Diagnostic work up Treatment options Outcome with medical management vs surgery Prognostic factors

4 Pathophysiology

5 Intervertebral disc (IVD) Three distinct compartments: Nucleus pulposus Glycosaminoglycans (GAG) Annulus fibrosus Endplates Atlas of Small Animal CT and MRI

6 Classification scheme: Hansen Type I Herniation of NP through AF with extrusion into the vertebral canal Chondroid metaplasia Chondrodystrophic breeds (CD) Type II Annular protrusion caused by shifting of central nuclear material Fibroid degeneration Nonchondrodystrophic breeds (NCD) Type III Traumatic disc Not defined by Hansen

7 Classification scheme: clinical IVD herniation (IVDH) Extrusion (IVDE) Atlas of Small Animal CT and MRI

8 Classification scheme: clinical IVD herniation (IVDH) Extrusion (IVDE) Protrusion (IVDP) Atlas of Small Animal CT and MRI

9 Classification scheme: clinical IVD herniation (IVDH) Extrusion (IVDE) Protrusion (IVDP) Acute noncompressive nucleus pulposus extrusion (ANNPE) Low volume high velocity disc extrusion

10 Classification scheme: clinical IVD herniation (IVDH) Extrusion (IVDE) Protrusion (IVDP) Acute noncompressive nucleus pulposus extrusion (ANNPE) Hydrated nucleus pulposus extrusion Atlas of Small Animal CT and MRI

11 Spinal cord injury Compression Concussion

12 Spinal cord injury Disruption of normal autoregulatory mechanisms Spinal cord perfusion becomes dependent on mean arterial pressure Subsequent ischemia/hypoxia may contribute to worsening spinal cord injury Cascade of events triggered by initial spinal cord injury Vascular Ionic Biochemical Contributes to injury and irreversible neuronal damage

13 Myelomalacia Softening of the spinal cord Focal Self limiting Ascending and descending myelomalacia (ADM) Severe spinal cord injury with resultant lack of nociception Auto-destructive process Hemorrhagic and non-hemorrhagic infarction spreading from initial site of impact Pathogenesis unknown Suspected to be end stage result of ischemic and circulatory processes Incidence: ~10% of cases with absent nociception

14 Incidence of thoracolumbar IVDE

15 Thoracolumbar disc extrusion: incidence IVDD: most common neurologic disease Levine et al. J Neurotrauma 2011 Th-L IVDE 2.3% of all admissions to veterinary teaching hospitals Hoerlein IVDD 2.02% of all diseases diagnosed in dogs Bergknut et al. JAVMA 2012 Sweden; veterinary health and life insurance records Lifetime prevalence of IVD degeneration-related diseases = 3.5% Incidence = 0.3% dogs per year Miniature dachshund, standard dachshund, doberman

16 Thoracolumbar disc extrusion: incidence Young to middle age CD: 4-6 years NCD: 6-8 years Male Chondrodystrophic breeds 48-72% of all affected = dachshunds Lifetime incidence approaches 20% Nonchondrodystrophic breeds Labrador German shepherd

17 Thoracolumbar disc extrusion: incidence Th-L region: most frequently affected 83.6% - between T11-L3 Chondrodystrophic T/L junction +/- 2 disc spaces Griffin et al nonchondrodystrophic 92% extrusion, 8% protrusion Large breeds L1-2 Cudia and Duval. JAAHA 1997.

18 Clinical signs

19 Clinical signs: T3-L3 myelopathy Mentation: Normal level and quality of consciousness Gait: UMN paresis/gp ataxia in pelvic limbs to paraplegia Postural reactions: Delayed to absent postural reactions in hind limbs Muscle tone: Normal tone in thoracic limbs; exception - schiff-sherrington Normal to exaggerated tone in pelvic limbs; exception - spinal shock Spinal reflexes: Normal to exaggerated patellar reflexes (clonic) Normal flexor withdrawal and perineal reflexes; exception - spinal shock Panniculus cut off ~ 2 vertebra caudal Nociception: Normal to absent caudal to level of lesion

20 Schiff-sherrington posture

21 Schiff-sherrington posture Peracute spinal cord injury Release of thoracic limb extensor muscles from normal inhibitory stimulus originating in thoracolumbar spinal cord Normal forelimb postural reactions Not a prognostic factor

22 Spinal shock Loss of supraspinal input on: Motor neurons Loss of muscle tone and spinal reflexes caudal to severe spinal cord injury Sympathetic neurons Bradycardia, bradyarrhythmias Reduced cardiac output Drop in MAP Time course of recovery Misleading for localization Not a prognostic factor Contribute to secondary SCI

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25 Differential diagnoses

26 Differential diagnoses Signalment History Speed of onset Lesion symmetry Presence of paraspinal hyperesthesia

27 Differential diagnoses Vascular: FCEM; infarction; hemorrhage Inflammatory: infectious meningomyelitis; spinal epidural empyema; discospondylitis; meningomyelitis of unknown etiology Trauma: vertebral fracture/luxation Anomalous: malformation Metabolic Idiopathic Neoplasia: primary; metastatic Degenerative: IVDE; ANNPE

28 Diagnostic work up

29 Minimum database Laboratory data: CBC Chemistry profile Urinalysis +/- culture Blood pressure measurement Radiographs: +/- chest radiographs +/- spinal radiographs

30 Survey radiographs Advantages Availability Sedation Cost Disadvantages Lacks accuracy No information about spinal cord Screening tool for certain differentials Surgical anatomy (v/d) CXR Platt Small Animal Neurological Emergencies

31 Commuted tomography (CT) Advantages Availability Cost Sedation or GA Speed Mineralized discs Disadvantages Myelography Multiple sites of compression No information about spinal cord Platt Small Animal Neurological Emergencies

32 Magnetic Resonance Imaging (MRI) Advantages Intraparenchymal pathology Hemorrhage Prognostic information Disadvantages Cost Time Limited information about bone T2 T2 L1 L2

33 Parameter: T2 hyperintensity > length of L2 vertebral body Successful outcomes following decompression: 100% - no hyperintensity 55% - hyperintensity 31% - hyperintensity + loss of nociception 10% - hyperintensity >3x length of L2 + loss of nociception Huge limitation: 0.3 tesla magnet Conclusion: more significant intramedullar change may be associated with a lesser degree of recovery

34 Parameter: T2 hyperintensity > length of L2 vertebral body Successful outcomes following decompression: 100% - no hyperintensity 55% - hyperintensity 31% - hyperintensity + loss of nociception 10% - hyperintensity >3x length of L2 + loss of nociception Huge limitation: 0.3 tesla magnet Conclusion: more significant intramedullar change may be associated with a lesser degree of recovery CONCUSSIVE INJURY ~> more permanent neurologic damage

35 Intramedullar T2 hyperintensity 100% ~6-20x length of body of L2 Intramedullar T2 hypointensity 10% Parenchymal hemorrhage

36 MRI findings: ascending descending myelomalacia Intramedullar T2 hyperintensity 100% ~6-20x length of body of L2 Intramedullar T2 hypointensity 10% Parenchymal hemorrhage T2 T2 T2

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38 Treatment options

39 Management strategies Based on clinical experience of the clinician Lack of controlled scientific studies Recommendations based on: Presenting neurologic status Signalment; likelihood of etiology other than IVDE Level of discomfort Previous attempt at medical management Financial situation of owner; insurance MRI findings Minimum database: CBC/chemistry/UA +/- culture BP +/- SXR

40 Management strategies Medical management Ideally reserved for ambulatory dogs with back pain alone or mild neurologic dysfunction Financial limitations Surgical decompression Nonambulatory dogs Rapidly progressive signs Lack of improvement or decline with medical management Recurrent episodes of back pain uncontrolled by medication Degree of spinal cord compression on MRI Medical management guidelines apply postoperatively

41 Medical management Enforced rest for 4-6 weeks Allow healing of torn annulus fibrosis Prevent further disc herniation Medications IVF: maintain spinal cord perfusion Analgesics Anti-inflammatories NSAIDs Corticosteroids Both veterinary and human studies have continually failed to show consistent benefit Potential for higher complication rate Physical rehabilitation

42 Medical management Weight control Avoidance of jumping activities/stairs/furniture Controlled leash activities Chest harness Immediate crate rest if painful/neurologic

43 Surgical management Goals: Removal of disc material and hemorrhage Minimal spinal cord manipulation Procedures: Hemilaminectomy Mini-hemilaminectomy Pediculectomy Partial corpectomy Dorsal laminectomy

44 Surgical management: fenestration Surgical removal of NP via a lateral window made into AF Theory: recurrence at site of fenestration decreased Prevalence without fenestration: % Prevalence with fenestration: % Brisson et al. JAVMA 2004

45 Surgical management: fenestration Opposing arguments Iatrogenic vertebral column instability Promotion of herniation at adjacent sites Reported complications: Disc extrusion Discospondylitis Hemorrhage Risk of wound infection Pneumothorax Increased intraoperative times Increased client cost Anesthesia related side effects

46 Outcome

47 Assessment of outcome Limitations: Inconsistent follow up Variable definitions of successful outcome Limited comparison studies Limited medical management studies based on diagnosis Majority of data based on surgical decompression

48 Outcome: medical management Interpret success rates cautiously: majority of studies are not based on MRI diagnosis Successful outcome based on neurologic status: Thoracolumbar pain and/or mild paresis: % Recurrence: 30-50%; typically within 6m-1y Nonambulatory paraparesis/plegia, intact nociception: 43-51% Paraplegic, absent nociception: <5%

49 Outcome: medical management Proportion of dogs with successful outcomes = 122/223 (55%) 6/15 (40%) paraplegia 13/23 (56%) nonambulatory paraparesis 30/63 (48%) ambulatory paraparesis 73/122 (60%) pain only Duration of cage rest not associated with outcome Administration of glucocorticoids negatively associated with outcome Recurrence: ~30% Significant limitations based on study design Client questionnaires: 303/1251 (24%) response rate Imaging: 40/303 spinal radiographs; 2/40 - myelography

50 Outcome: surgical management Successful outcome based on status of nociception: Intact nociception: 79-96% Median time to regain ambulatory function: 9 days Absent nociception: 43-78% Median time to regain ambulatory function: 7.5 weeks Long term outcome appears to be independent of: Location of herniation Degree of compression Duration of clinical signs Time to decompression

51 Recurrence: surgical management Mayhew et al. JAVMA /229 (19.2%) clinical signs associated with recurrence No fenestration; back pain only not considered recurrence Within 3 years of decompressive surgery 96% (median follow up: 3.7 years) Dachshunds 25% Other breeds 15% Risk increased with number of opacified discs (1.4 times per disc) Dhupa at al. Vet Surg /467 (6.4%) reoperated 0/30 - fenestration of adjacent discs at first surgery Early reoperative cases (<4 weeks): 5 residual disc material Late reoperative cases (>4 weeks): 25 second site

52 Summary: successful outcomes Spinal hyperesthesia Medical 55-85% Surgical 96% Ambulatory paraparesis 55-85% 86-96% Nonambulatory paraparesis 55-85% 86-96% Paraplegia, intact DPP 50% 79-96% Paraplegia, absent DPP 5%* <12-24h: 43-79%* >24-48h: 6-33%*

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54 Prognostic factors

55 Prognostic factors Consistent: Presence of nociception Controversial: Duration to nonambulatory status, Scott 1999, Ferreira 2002 Rapidly progressive poorer outcome Duration of clinical signs, Ferreira 2002 Postoperative ambulatory function, Davis 2002, Garrett 2002 Recovery of nociception, Scott 1999 Positive if returns in 2-4 weeks

56 Prognostic factors Controversial: Spinal cord T2 weighted hyperintensity, Ito 2005 Poorer prognosis with increasing length on sagittal MR images Subdural hemorrhage viewed grossly at surgery, Ito 2005 Spinal cord swelling > 5 times length of L2, Duval 1996

57 Conclusion

58 Summary TL IVDE common neurologic disease resulting in spectrum of dysfunction MRI diagnostic tool of choice for diagnosis and making treatment recommendations Decision between medical management and surgical decompression multifactorial Limited medical to surgical comparisons Benefit of surgery over medical management not well defined Majority successful outcomes following decompression in dogs with intact nociception Timing of surgery not well studied in veterinary medicine Within 24 hours of onset of nonambulatory status

59 Questions?