Traumatic spinal cord injury (Proceedings)

     • Primary injury

          o Direct parenchymal and vascular damage

          o Occurs immediately as a result of traumatic event

     • Secondary injury

          o Result of biochemical cascades initiated by primary injury

          o Includes ATP depletion, increases in intracellular Na+ and Ca2+ as well as extracellular excitatory neurotransmitters, production of oxygen free radicals, increased cytokine production, accumulation of nitric oxide, lactic acidosis and activation of arachidonic acid, kinin, complement, coagulation and fibrinolytic cascades

          o Results in further damage to nervous tissue

          o Therapy directed at minimizing secondary injury

     • Initial neurologic evaluation

          o Important components of neurologic exam

               ▪ Motor/Posture – ambulatory vs. recumbent, muscle tone and voluntary movements, Schiff-Sherrington posture

               ▪ Segmental reflexes – tendon, withdrawal, panniculus and perineal reflexes

               ▪ Pain perception – assessed via behavioral response to a noxious stimulus

                    » Superficial – elicited from pinch of the skin/SQ tissues

                    » Deep – elicited from pinch of bone/digit

               ▪ Mentation and cranial nerve evaluation can generally be performed without significant patient manipulation

          o Scoring system has been described for acute spinal cord injury in dogs

          o Initial neurologic status may improve following immediate stabilization

     • Management of TSCI

          o Immobilization

          o Hemodynamic stabilization

               ▪ Resuscitation for maintenance of normotension, adequate oxygen levels

                    » Often concurrent injuries involving other areas – cardiovascular, respiratory, abdominal, brain trauma

               ▪ CBC, chemistry panel, electrolytes, UA and thoracic radiographs can help define extent of injuries

          o Analgesia

          o Imaging

               ▪ Radiographs – screening lateral views safe; VD views only with a horizontal beam technique if potential for instability exists

               ▪ CT – excellent bone detail, evidence of hemorrhage may be seen

               ▪ Myelography – used to evaluate potential spinal cord compression

               ▪ MRI – for evaluation of extrinsic and intrinsic spinal cord lesions

          o Medical management to reduce secondary injury

               ▪ Corticosteroids

                    » Use controversial in human and veterinary medicine

                    » Methylprednisolone has been extensively evaluated; evidence suggests benefit related more to free radical scavenging than anti-inflammatory properties; other commonly used steroids (e.g. prednisone, dexamethasone) do not have free radical scavenging capabilities

                    » National Acute Spinal Cord Injury Study trials in humans

                        o Small improvements (in motor scores at 6 weeks and pinprick and touch sensation at 6 months post injury) noted in TSCI patients administered methylprednisolone within 8 hours of injury; detrimental >8h; no difference in outcome vs. control groups at 1 year; increased risk of pneumonia and trend towards sepsis with methylprednisolone therapy

                    » A study in dogs showed timely surgical decompression of acute compressive spinal cord injury was more effective for improving neurologic recovery than methylprednisolone without surgery

                    » A study of dachshunds administered methylprednisolone and having surgical decompression following IVD herniation showed increased post-operative complications (melena, diarrhea, emesis, hematemesis and anorexia) and higher medical bills vs. dogs not receiving methylprednisolone Polyethylene glycol (PEG)

                    » Use shown to be safe in dogs

                    » Ongoing studies for evaluation of efficacy in spinal cord injury

               ▪ N-acetylcysteine has been investigated to prevent oxidative secondary injury in dogs, but did not prove to have clinical benefit in a randomized blinded placebo-controlled clinical trial

          o Management of vertebral instability/fractures/luxation

               ▪ Non surgical treatment

                    »Similar long term outcomes vs. surgery in several retrospective studies

                    » Confinement – mandatory for suspected instability, =6 weeks

               ▪ External support – for immobilization of vertebral segments cranial and caudal to lesion; variably tolerated from patient to patient

                    » Potentially less expensive vs. surgical therapy, but more labor intensive, longer recovery and potentially a greater risk of persistent deficits

               ▪ Surgical decompression/stabilization

                    » Indications include minimal voluntary movement, evidence of highly unstable fractures and progression of signs despite appropriate non surgical treatment

                    » A variety of methods of stabilization have been reported

               ▪ Oscillating electric field – has shown some initial promise in dogs with complete transverse myelopathy

               ▪ Low level laser therapy also being investigated in dogs

          o Prognosis and complications

               ▪ Prognosis for return of function with loss of deep pain perception generally considered grave; in one study of cervical vertebral fractures in dogs, severity of neurological deficits (nonambulatory status) and prolonged interval (five days or longer) from trauma to referral were associated with poorer outcome

               ▪ Persistent neurologic deficits possible

               ▪ Hypoventilation possible with cervical trauma/surgery

               ▪ Myelomalacia possible in association with of loss of pain perception

               ▪ Additional complications of recumbent patients, including aspiration pneumonia, UTI, pressure sores

Suggested reading:

Spinal Fracture or Luxation, Bagley, RS, The Veterinary Clinics of North America: Small Animal Practice, Common Neurologic Problems, 30(1), 2000

Bracken MB et al, A randomized, controlled trial of methylprednisolone or naloxone in the treatment of acute spinal cord injury. Results of the Second National Acute Spinal Cord Injury Study. N Engl J Med, 1990; 322(20):1405-1411