What to do with the acutely paralyzed dog?
The 48 hour rule: Is it a myth?
My article summary conclusions and recommendations (in case no time to read the whole article):
· Published in JAVMA February of this year, Jeffery et. al. have helped to dispel the dogma that ability to regain ambulation in acutely paralyzed deep pain negative dogs is related to time to surgery. In this prospective cohort study looking at 78 acutely paralyzed deep pain negative dogs, all of which had advanced imaging and surgery for IVDH, time between onset of signs and surgery was NOT linked to prognosis. “In this group of dogs with IVDH (intervertebral disk herniation), immediacy of surgical treatment had no apparent association with outcome. The prognosis for recovery may instead be strongly influenced by the precise nature of the initiating injury”. These dogs are more likely to experience contusion, edema and hemorrhage of the spinal cord as a result of high velocity IVDH, and may or may not have significant cord compression. Link to article abstract here: http://avmajournals.avma.org/doi/abs/10.2460/javma.248.4.386
· The article strongly suggests that acutely paralyzed deep pain negative dogs MAY NOT need to be rushed to surgery as soon as possible to improve prognosis; prognosis for recovery will be in the 50% range in nearly all of these cases. About 10% of these dogs may be at risk for ascending/descending myelomalacia which is often fatal.
· Dogs experiencing rapidly progressive (2 weeks or less) paresis>>>paralysis DO have surgical urgency. These dogs tend to have severe spinal cord compression from IVDH, and their prognosis for full or near full recovery with spinal cord decompression is 90%+. That prognosis falls off the longer surgery is delayed.
· Dogs with both moderate and severe neurological deficits need MRI to help define both the reversibility of the condition and the need for surgery or not
· …for explanations, keep reading.
The study. Published in JAVMA February of this year, Jeffery et. al. have helped to dispel the dogma that ability to regain ambulation in acutely paralyzed deep pain negative dogs is related to time to surgery. In this prospective cohort study looking at 78 acutely paralyzed deep pain negative dogs all of whom had advanced imaging and surgery for IVDH, time to surgery (even if delayed beyond 48 hours) did not effect prognosis in a statistically significant way. “In this group of dogs with IVDH (intervertebral disk herniation), immediacy of surgical treatment had no apparent association with outcome. The prognosis for recovery may instead be strongly influenced by the precise nature of the initiating injury”.
For as long as I can remember, the rule was that an acutely paralyzed dog (presumably due to IVDD) needed to have surgery within 48 hours of paralysis…or else! The world would implode, the sun would begin rotating backwards…this is a real emergency folks and this dog needs surgery NOW! Such WAS the rule.
Intuitively, the storyline is easy to buy into. Presumably a disk has herniated. Presumably, the disk is exerting pressure on the spinal cord. Presumably removing that pressure from the spinal cord will give the dog the best chance of recovery…the sooner the better. But where did the 48 hour rule come from? Where is the data to support the rule? In large part from experimental data using laboratory animals.
Early in my career, like everyone else, I bought into the rule. Over time I realized there was a problem with it. Many acutely paralyzed dogs recovered with delayed surgery or even without surgery! Many dogs with timely surgery (often at midnight) never recovered the ability to walk. Which dogs would walk again and which would not seemed a random event. Senior neurologists I spoke with shared these experiences and sentiments. Something about the rule did not make sense. But because the rule existed as the ‘gold standard’, we followed along…skeptically.
Experientially, if a dog became acutely paralyzed without deep pain sensation in its toes, it had only a 50% chance of ever walking again whether it had spinal decompressive surgery in the first 48 hours or not. The advent and common use ofMRI in vet med began to offer clues. We could see the damage to the spinal cord from acute IVDH (intervertebral disk herniation). We saw significant spinal cord edema, swelling and hemorrhage, but often very little active compression. In 2 cases that I have personally seen, and in one published case report, herniated disk fragment actually penetrated the meninges and spinal cord. This speaks to the force and velocity with which nucleus pulposus can herniate. It also helps to explain the impact component in acute disk rupture. It’s this impact injury that probably dictates the reversibility of the spinal cord injury in these acute injury cases, and to a lesser extent, the degree of spinal cord compression, although both certainly play a role. There is no doubt in my mind that relieving even moderate compression sets the stage for optimal cord recovery. But the impact event is likely to be the more important determinant of injury reversibility.
And then there was another experiential observation. In acute, higher velocity disk herniations causing acute paralysis, the herniated nucleus pulposus (jelly center of the disk) tends to be more liquid, lower viscosity, and therefore less compressive after it ruptures into the spinal canal. In contrast, very mineralized high viscosity nucleus(like toothpaste or cream cheese consistency) tends to herniate with lower velocity but be more compressive; causing more slowly progressive signs in the dog. Semi-liquid low viscosity nucleus>>>high velocity herniation, greater impact>>>acute severe signs. Mineralized high viscosity nucleus>>>low velocity herniation, less impact but greater compression>>>slowly progressive signs. To illustrate: If you apply the same amount of pressure to a tube of toothpaste and a tube filled with water, then pop the top, which material will erupt with greater velocity? Greater velocity means greater impact and generally, less compression. Slower velocity means less impact, but generally, greater compression. The latter is more reversible and carries better prognosis. The spinal cord is compressed, but not traumatically injured, and therefore the reversibility is increased…when compression is relieved.
Ahhhh. Deep sigh of relief from me, as I’ve been telling people for years, as a point of argument, that of all the subsets of IVDD patients, the acute paralyzed deep pain negative dog MAY be the WORST candidate for spinal surgery…an argument against the widely held belief that spinal surgery should be reserved for that subset of patients alone. A $3500-7000 (sometimes more) investment with only a 50-60% chance of recovery is not the return on investment owners are after, particularly when most other spinal surgery patient subsets have 90% or greater recovery rates.
The moral of the story? The surgical option for IVDD patients should not be reserved for ONLY those most severely affected…the acute paralyzed deep pain negative subset in particular. Spinal surgery is more effective for other subsets of IVDD dogs; those with chronic signs, those with recurrent signs, those with moderate deficits, and most importantly, those whose signs are progressive (the more rapidly progressive the more urgency for surgery NOW).
For the acute paralyzed deep pain negative dog, the conversation about surgical success or failure is more important than rushing the dog off to surgery, and understanding why is necessary to intelligently have that conversation.
The 48 hour window….pffff! NO need to rush off to CSU or elsewhere if I’m not immediately available, and no need to call me in the middle of the night (although that is OK too).