Joan Capuzzi Giresi, VMD
Intervertebral disk disease in dogs can be a devastating diagnosis, with treatment decisions often based both on the neurologic status of the patient and the economics of the owner.
leungchopan/stock.adobe.comThe intervertebral disks-flexible pads between the vertebrae-function as shock absorbers for the vertebral bodies and the overlying spinal cord.
“They cushion the blow during activity,” explained Simon Platt, BVM&S, FRCVS, DACVIM, DECVN, professor of neurology at the University of Georgia College of Veterinary Medicine, at the 2019 Atlantic Coast Veterinary Conference.
The disk consists of a gelatinous substance (nucleus pulposus) encased and stabilized by a rigid ring (annulus fibrosus). When disk material herniates and compresses the spinal canal secondary to either degeneration of disk material or traumatic forces, the result is intervertebral disk disease (IVDD).
Classifying disk disease
The various types of disk disease are linked largely to signalment and patient history. In Hansen type I IVDD, the degeneration of proteoglycans in the central nucleus pulposus results in dehydration, collagenization and mineralization of the gel. The hardened pulposus then extrudes through the annulus fibrosus and compresses the spinal canal. The resulting spinal contusion causes spinal cord ischemia, electrolyte changes and neurogenic shock, and can even occasionally result in systemic hypotension.
This acute condition is an emergency, and the patient should be stabilized rapidly with oxygen and fluids, Dr. Platt said.
Chondrodystrophic breeds, like dachshunds and Welsh corgis, are genetically predisposed to type 1 IVDD. By age 2, said Dr. Platt, nine out of 10 chondrodystrophic dogs have degenerative changes in their disks. These dogs typically present with clinical signs around age 5.
Hansen type II IVDD, by contrast, occurs most commonly in older (mean age 7-8 years), large-breed dogs. Here, natural dehydration and mineralization of both the pulposus and the surrounding fibrosus occur over time. These chronic changes lead to disk bulging and spinal cord compression. Rest and anti-inflammatory medications can often alleviate clinical signs and stall progression.
Acute noncompressive nucleus pulposus extrusion (commonly referred to as Hansen type III IVDD) occurs more frequently in large breeds but can strike any dog. It is not degenerative; rather, it involves trauma that tears the annulus and allows normal nucleus to explode through. Because the gel disperses, there is typically no ongoing cord compression or pain. These patients usually do not require surgery, and they respond well to anti-inflammatories and rehabilitation.
The worst sequela of traumatic IVDD is progressive myelomalacia. This condition, which afflicts some 10% of dogs with severe IVDD (those that are paralyzed with a loss of nociception), involves ischemic necrosis and liquefaction of the nerve tissue. This rapid cell death ascends and descends along the spinal cord, away from the original lesion, beginning within 72 hours of injury. Characterized by paraplegia, profound pain, hyperthermia, incontinence, abnormal respiration and eventual loss of reflexes, myelomalacia is usually ultimately fatal.
The IVDD crystal ball
IVDD is graded based on clinical signs. This grading system helps determine course of treatment and prognosis associated with different options:
Grade 1: Back pain without motor impairment
Grade 2: Ambulatory paraparesis
Grade 3: Non-ambulatory paraparesis
Grade 4: Paraplegia with deep pain perception
Grade 5: Paraplegia without deep pain perception.
Chronicity does not factor directly into grading, Dr. Platt explained.
“Acute onset doesn't imply prognosis,” he said. “What indicates prognosis is the presence or absence of deep pain perception or nociception.”
For a dog that has pain sensation, the overall chances of recovery are 80%. If pain sensation is absent, the chances drop to 50%, and recovery is almost 0% with concurrent spinal fracture.
Dr. Platt questioned the use of radiography for chondrodystrophic breeds, noting that plain radiographs will almost always indicate disk mineralization - even in young Bassets or beagles, for example - but often will fail to confidently identify the pertinent herniated disk(s). Radiographs are more useful for non-chondrodystrophic breeds to rule out other differentials, such as diskospondylitis or neoplasia.
If surgery is planned, he recommended computed tomography (CT) or magnetic resonance imaging (MRI) to confirm and localize the lesion(s); CT, he noted, is faster and more affordable for clients and can be as accurate in many cases.
To cut or not to cut
Factors to consider when developing a management plan include neurologic status, lesion location, concurrent illness and medical treatment, presence or absence of previous episodes, method of diagnosis and economics; ultimately, said Dr. Platt, the decision between medical and surgical treatment comes down to patient neurologic status and dog owner economics.
Successful recovery from IVDD, he continued, means the patient is no longer painful, can ambulate without assistance and has urinary and fecal continence.
For grades 1 and 2 IVDD, both medical and surgical management yield 90% recovery. For grade 3, surgery excels over medical management (90% vs. 70% recovery, respectively). The gap widens for grade 4 IVDD; 80% to 90% of patients recover with surgery, whereas 50% recover with medical treatment. Patients with grade 5 disk disease are less than 5% likely to recover following medical management. Prognosis with surgery in these patients is time dependent: Surgery within 48 hours of clinical onset carries a 60% chance of recovery, but this drops to less than 5% around the one-week mark.
Dr. Platt described the criteria for surgery: paralysis on presentation, worsening neurologic status despite medical treatment, refractory spinal pain despite medical treatment, and recurrent episodes of spinal pain that worsen successively.
For medical management alone, Dr. Platt recommended low-dose (0.5-1 mg/kg/day), short-course prednisone or nonsteroidal anti-inflammatory drugs; he said he prefers prednisone because of its superior effect in spinal analgesia and for chronic and/or severe compression. Adjunctive treatment includes gabapentin, opioids and muscle relaxants such as methocarbamol and diazepam.
Nursing care for these patients should include four to six weeks of cage rest, adequate padding and nonslip mats, sternal recumbency (or lateral recumbency with turning every 4 hours), monitoring for decubital ulcers, feeding assistance, bladder management and such supportive therapies as physical therapy, hydrotherapy, laser therapy and acupuncture.
With medical management, 25% of cases will recover with no recurrence, 25% will recover with recurrence within one year, 25% will recover with recurrence within two years and the remaining 25% will deteriorate without surgery.
For the medical-versus-surgical dilemma in first-presentation cases of grade 1 to 3 IVDD, he said, “We let owners make the decision based on the fact that the majority will get better, but 50% will have a recurrence.”
The intervertebral disks, though small and well concealed within the spinal meshwork, are critical to function and life itself. Fortunately, there are good medical and surgical protocols to address the debilitating effects of disk failure.
Dr. Capuzzi, who earned her BS and VMD degrees from the University of Pennsylvania, works in small animal practice in the Philadelphia area and is a published author. She has written for The Philadelphia Inquirer, Time, Business Philadelphia, Dog Fancy and Dog World, among others. She is especially interested in public health and animal welfare, and is involved with several organizations whose missions are to improve the lives of domesticated and wild animals.