Traumatic Injury to the Equine Central Nervous System, ACVIM 2009

Whether it's a yearling that flipped and landed on his poll or an older horse that tumbled after simply taking a bad step, traumatic injury to the central nervous system is the most common cause of neurologic problems in horses. Yvette S. Nout, DVM, MS, PhD, Dipl. ACVECC, ACVIM, a researcher at the University of California, San Francisco, reviewed the pathophysiology and therapeutic options for treating these animals at the American College of Veterinary Internal Medicine Forum, held June 3-6 in MontrĂ©al, Quebec.

Nout reported that central nervous system trauma accounts for 24% of equine neurologic cases, with approximately equal distribution between spinal cord trauma and traumatic brain injury. Although some aspects of the pathophysiology in these types of injuries are different, many of the underlying mechanisms for cell damage are similar, and treatment approaches for both focus on reducing inflammation and swelling, stopping secondary injury, and aiding regeneration for a functional outcome.

She noted that the prognosis for these horses is greatly dependent on the severity of the primary injury and on the location and extent of the damage.

While head injuries are considered to occur fairly commonly in horses, traumatic brain injury occurs in only 25-50% of these cases, with the most severe injuries to the brain occurring within a closed (non-fractured) calvarium, which restricts swelling of brain tissues. The subsequent disruption of bloodflow and oxygen delivery ultimately leads to cell death.

"There is limited space within the skull that is occupied by brain tissue, blood volume, and cerebrospinal fluid (CSF), the fluid that surrounds the nervous system," Nout explained. "If a change occurs in the volume of any of these three compartments, this directly affects the volume of the other compartments.

"For example, if the brain is injured and swells (a common response of all tissues after injury), there will be less space to accommodate the blood volume and CSF. This means less blood will be able to enter the brain and this reduction of blood flow to the brain is critical. In any injured and subsequently swollen tissue it is more difficult to get oxygen and nutrients to the cells that need it, even if blood flow is optimal. Adding a reduction of blood flow to the presence of injured tissue, such as seen in closed head injuries, confounds the problem and increases the risk of further injury to the cells," Nout said.

Trauma to the vertebral column is most often caused by a collision or fall, with trauma or fractures of the cervical vertebrae (the neck) being the most common.

In both brain and spinal cord injury, delayed tissue damage can result due to a complex array of events taking place on the molecular, cellular, and biochemical levels. The goal of treatment is to minimize secondary injury to the tissues that survived the original mechanical injury. But because the factors surrounding potential cell death following primary injury are so complex, a single drug interaction is unlikely to provide a miracle cure.

Nout covered several combinations of treatments to optimize delivery of oxygen and reduce secondary injury with the goal of salvaging brain/spinal cord tissues. Some of the treatments discussed included blood transfusion, fluid therapy (including serum versus albumin and hypertonic versus isotonic fluids), as well as the use of non-steroidal anti-inflammatories, DMSO, and corticosteroids. In addition, Nout shared results of combinatorial treatments that include use of cell transplants and local growth factor injections under experimental conditions.

"Optimizing systemic blood pressure during the acute stage of injury is critical in order to maintain delivery of oxygen to the central nervous system," Nout said. "Depending on amount of blood loss that may occur during trauma, this is best done by intravenous blood transfusions, blood products, or hyper- or isotonic fluids and use of vasopressors/inotropes when necessary.

"The two most common routes of reducing swelling in the acute stage of injury is administration of mannitol and/or hypertonic saline, both of which ultimately shift fluid away from swollen tissues back into the vascular space. Combining these treatments with the goal to optimize oxygen delivery to the injured tissues can occur, preferably while blood pressure fluctuations and blood sodium concentrations are closely monitored.

"In equine medicine, treatments to reduce inflammation and effects from free radicals are commonly used. Examples are drugs such as flunixin (Banamine), dimethyl sulfoxide (DMSO), and corticosteroids. Whether these drugs truly have positive effects on outcome in equine CNS trauma is still unknown," Nout noted.

She noted that while surgical intervention to stabilize surrounding areas, repair fractures, or relieve pressure might sometimes be indicated, it is not a routine practice, except in the surgical treatment of certain skull fractures (bones around the eyes, sinuses, and jaw bones). Even when emergency decompressive surgery is undertaken, pre-operative medical treatment should always be attempted as the first line of defense.

"In situations in which your horse undergoes a traumatic event such as falls or collisions with gates or other horses, etc., have your vet perform a thorough neurological examination in addition to the physical and orthopedic exam, and treated if necessary," Nout said. "Repeat neurologic examination may be necessary since sometimes onset of (milder) neurologic disease after trauma is delayed."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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