34th Annual Scientific Meeting proceedings

Absence of pain perception or nociception is a well-recognised prognostic factor in animals with acute spinal disease. Although absence of pain perception is associated with a guarded to poor prognosis, deep pain negative dogs with acute intervertebral disc extrusion (IVDE) can still experience a complete neurological recovery. This complicates clinical decision making and can represent an ethical dilemma. Clinical factors to consider when deciding if treatment should be attempted in a deep pain negative dog can include the underlying diagnosis, duration of deep pain negative status, imaging findings, animal specific factors, owner expectations, finances, and ability to provide appropriate post-operative care.

Underlying condition
Although deep pain negative dogs with acute IVDE can experience a successful recovery after surgery, this is less likely for other causes of acute spinal injury. It is unlikely that an animal with bilateral absent pain perception caused by ischaemic myelopathy or acute non-compressive nucleus pulposus extrusion will regain voluntary ambulation. It is extremely unlikely for an animal with absent pain perception caused by a fracture or luxation to regain voluntary ambulation. Failing to inform owners about such a poor prognosis should be considered unethical.

Duration of deep pain negative status and imaging findings
Although dogs with absent pain perception caused by acute IVDE can experience a successful outcome, it is likely that a progressive longer duration of a deep pain negative status is associated with a worse prognosis. Historically, it has been considered that if surgery can be performed within the first 24 hours after losing deep pain perception, 50% to 60% of dogs will experience a successful recovery. Likelihood of recovery then sharply decreases after this timeframe of 24 hours. This concept has recently been challenged and it is increasingly recognised that dogs with a longer duration of a deep pain negative status can still experience a successful recovery. It is further challenging to determine the exact moment when a paraplegic dog loses pain perception.

Several studies have evaluated the association of specific MRI variables and prognosis in dogs with acute IVDE. MRI findings suggestive for progressive myelomalacia are associated with a poor to grave prognosis. These findings include severe spinal cord swelling; extensive, poorly demarcated, diffuse intraparenchymal T2-weighted hyperintensities over several spinal cord segments; areas of T2-weighted hypointensity and signal void on T2* sequences (suggestive for haemorrhagic areas).

Although the prognosis of dogs with absent pain perception caused by spinal fracture and luxation is already poor to grave, the combination of absent pain perception and a 100% displacement of vertebral segments is associated with a hopeless prognosis. Not communicating such a hopeless prognosis with your clients should be considered unethical.

Animal specific factors
Recovery from severe acute spinal injury is most often associated with substantial lengths of hospitalisation, and long and intense recovery periods. This might be challenging for aggressive, anxious or very nervous dogs. Other animal specific factors that can influence the decision to attempt treatment are the size of the dog, age, previous lifestyle, and potential comorbidities. A proportion of deep pain negative dogs that undergoes surgery for acute IVDE will not regain the ability to voluntary ambulate and urinate. Some dogs can however experience a good quality of life with the assistance of wheelchairs and other supportive measures. Some spinal injuries can be very painful. Although it can be considered ethically acceptable to care for a permanently non-ambulatory dog, this should only be considered of the animal can have a pain-free and comfortable life.

Owner expectations
Spinal surgery for deep pain positive paraplegic patients is typically followed by a recovery period of several weeks to months. This timeframe is often much longer in deep pain negative dogs (if they recover at all). During this recovery period, patients require appropriate nursing care, including bladder management and physiotherapy. It is clear that owners should expect a gradual and slow recovery in which they will play an active role. It is crucial that, if surgery is performed in deep pain negative dogs, they should be given the time and opportunity to demonstrate improvement. Such a long recovery period is however also associated with large expenses. It is possible that not all clients will be able to accept such a long, slow and expensive recovery period. As discussed above, animal-specific characteristics can further complicate the road to recovery. Not informing and discussing the intensity and duration of the recovery process before planning surgery should be considered unethical.

Ability to provide appropriate post-operative care
As discussed above, recovery from severe acute spinal injury requires appropriate nursing and supportive care. Expertise and experience will facilitate recognising complications and assessment of outcome patterns. Spinal surgery in animals with spinal trauma should only be performed in hospitals that are able to provide adequate nursing care and are confident in assessing gradual and slow neurological recovery.