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Care of the Neurological Patient Natasha Olby Vet. M.B. Ph.D. Diplomate ACVIM (Neurology) Department of Clinical Sciences North Carolina State University, College of Veterinary Medicine Spinal Cases Introduction The spinal cord extends from the foramen magnum of the skull to the conus medullaris within the vertebral canal of the vertebral column. The vertebral column has the dual role of protecting the spinal cord from injury, and allowing movement of the spine. In order to facilitate movement, the vertebral column is composed of individual vertebrae that are linked by intervertebral discs and a complex system of ligaments and joints. This complicated anatomical arrangement predisposes the vertebral column to degenerative changes and makes it susceptible to traumatic injury. Definitions It is important to use the correct terms when describing neurological signs in order to accurately convey the clinical picture. The following terms are pertinent to spinal cord disease and will routinely be used by veterinarians.
Initial Assessment of a Spinal Case A) Supporting The Spine It is extremely important to understand that if the vertebral column has been fractured or luxated, moving the animal can cause movement of the vertebrae with the catastrophic result of causing further injury to the spinal cord. In addition, even if there is no instability, if there is a large compressive lesion within the vertebral canal impinging on the spinal cord, movement of the vertebrae can worsen this compression, again causing further injury to the spinal cord. Normally the spinal musculature helps to support the vertebral column but if the animal is sedated, the muscles will relax and the column effectively loses support. The take home message is that any paralyzed are paretic animal, whether or not there is a history of trauma, should be moved in such a way that the spine is supported. This is particularly important when the animal is sedated or anesthetized. If an owner calls to say their pet has suffered a traumatic injury, they should be advised to move them by placing them on a blanket that is held taught to provide support to their spine. They can be placed on a board and taped on, but there is potential for an owner to do this incorrectly or for the animal to be too painful to tolerate rigid immbolization. Once they reach the clinic, most clinics have a special stretcher that will allow the animal to be immobilized safely. Owners should also be warned that their pet may be in severe pain and could bite them out of fear and pain. B) Historical Points Once a patient reaches the clinic, the owner should be questioned carefully on the medical history. Specific questions include the duration of signs (in particular of paralysis), whether their animal has urinated and defecated recently, when it last ate, and what drugs have been administered. If the pet was involved in a traumatic accident, as many details of the accident as possible should be elicited. For example, if hit by a car, did the tires run over the animal, or was it a glancing blow. C) Physical Evaluation The speed and order of the patient assessment will of course depend on the history - an animal that has been hit by a car will be assessed and stabilized immediately. In all cases, useful parameters to assess in the pateint include a TPR and palpation of the abdomen to assess the bladder. The veterinarian will assess whether there is any motor function present (and how many legs are affected), spinal reflexes, sensation and presence of hyperpathia. The presence of sensation in affected legs is of paramount importance as it allows the veterinarian to assess the severity of the injury. If there is complete loss of sensation then the injury is extremely severe. Sensation is assessed by using forceps to clamp over the toe (just behind the point at which the nail joins the bone). Gentle pressure is exerted at first and in a normal dog, they may respond immediately by withdrawing the leg and looking around. The withdrawal of the leg is a reflex and does not provide information on the ability of the dog to be aware of the stimulus - it is important to watch for the dog's conscious response. If there is no conscious response to gentle presure (the dog simply wahtdraws the leg but does not look around), the pressure is increased again looking for the dog to signal that it is aware of the stimulus. D) Spinal Radiographs In order to obtain good quality spinal radiographs, it is usually necessary to sedate or anesthetize the patient. In some cases, sedation or anesthesia may be contra-indicated: for example a critically ill patient, or a patient with suspected unstable fractures or luxations in which the splinting effect of the spinal musculature plays a vital supportive role. As a general rule, any patient with suspected compressive spinal cord disease should be handled carefully when sedate, as there is less muscle tone and extension or flexion of the spine may exacerbate spinal cord compression or cause concussive injuries. Lateral projections are usually obtained first. The animal should be supported with foam pads and sand bags to obtain good lateral views with no rotation. To obtain good images of the caudal cervical spine, the thoracic limbs may have to be pulled caudally so that the shoulder doesn't overly the area of interest. In some diseases it is always advisable to radiograph the entire spine, even in the face of focal signs, in view of the multifocal nature of the disease. These include discospondylitis, trauma and certain types of cancer (e.g. multiple myeloma). Multiple projections of the spine should be obtained to allow accurate interpretation (the divergent path of the X-ray beam prevents interpretation of the width of disc spaces at each end of the image.) Coned radiographs should be centered over certain problematic areas including the atlantoaxial junction, the caudal cervical spine, the thoracolumbar junction and the lumbosacral junction. Once it has been established that it is safe to turn the animal (in the case of trauma) from the lateral radiographs, the animal should be placed on its back and ventro-dorsal (VD) projections obtained. In cases that have potentially unstable fractures or luxations, a horizontal beam should be used to obtain this view to avoid moving the animal. Ongoing Care of the Spinal Case A) The Bladder Storage of urine and successful voiding (micturition) at an appropriate time is a complex process achieved by the coordinated relaxation and contraction of the detrusor muscle and the internal and external urethral sphincters. The bladder is innervated by 3 different types of nerve all coming from the spinal cord
Urination can be divided into storage and voiding phases. During the storage phase, sympathetic activity produces relaxation of the detrusor muscle and contraction of the internal urethral sphincter. The external urethral sphincter is also contracted and sudden increases in intra-abdominal pressure (for example when coughing), produce immediate increases in external urethral sphincter tone. At a certain threshold level of distension of the bladder, the sensation of a full bladder is transmitted to the micturition center and the animal becomes aware of the need to urinate. When it voluntarily decides to urinate, the abdominal muscles contract, perineal muscles relax and the micturition reflex causes a decrease in tone in the internal and external urethral sphincters and contraction of the detrusor muscle. There is also a reflex that prevents concurrent urination and defecation. Neurogenic incontinence is frequently divided into upper versus lower motor neuron (UMN and LMN) incontinence. Upper motor neuron incontinence results from spinal cord lesions above the level of the sacrum and LMN incontinence occurs with sacral spinal cord lesions. It is also possible to have autonomic incontinence with dysautonomias.
Any disease of the spinal cord severe enough to cause paraplegia causes UMN urinary incontinence. The following steps should be taken to ensure optimal recovery:
B) Skin Care Recumbent patients are at risk from developing decubital ulcers over pressure points and urine scald. Urine scald can be prevented by
Any patient that is tetraparetic or plegic (unable to use all 4 legs), and therefore recumbent is at risk of developing aspiration pneumonia, atelectasis (collapse) of a lung, or hypoventilation. It is very important to assess the completely recumbent patient's ability to breath by watching the pattern, rate and depth of respiration. As a general rule, they are able to expand their lungs better when sitting sternally. If their neurological disease is very severe, they may not have the strength to move their ribcage and diaphragm enough and such cases need ventilator support. Aspiration pneumonia tends to occur in these patients because food leaks back along the esophagus, and atelectasis simply occurs secondary to gravity. To optimze lung function in tetraparetic patients
Physical rehabilitation is best performed at a dedicated rehabilitation center but this does not mean that patients should not receive basic rehabilitation at all times. This helps to slow degeneration of joints, muscles and bones, is often pleasant for the animal, and can help to control pain. Basic exercises that can be performed include passive range of motion exercises in which the affected limb is put through full extension and flexion, massage (of whole body), and supported walking (using a cart or slings). It is always a good idea to feed the animal when it is upright and preferably standing (as it normally would be). This can be achieved by placing them in a cart. Summary As people entrusted with the medical care of a patients, it is extremely important that we follow the well known rule - first do no harm. This applies to spinal patients in which a careless move can cause a severe injury, and negligent care can result in severe decubital ulcers and permanent damage to the bladder. As the technician, you will be closely involved with each patient and should pay special attention to their skin, their breathing, their bladder and their pain level. Do not be afraid to point out any problems you see developing to the veterinarian in charge of the case and remember that prevention is better than a cure. Seizure Management: Diagnostic and Therapeutic Principles Introduction Seizures are paroxysmal, synchronous neuronal discharges, typically originating in the cerebral cortex. Epilepsy is a general term that refers to recurrent seizures of any type and can be divided into different etiologic categories:
Generalized seizures involve the body symmetrically and are typically (but not always) tonic-clonic (grand mal). The seizure starts with the tonic phase (limb extension) and loss of consciousness, and this is followed by clonus (limb flexion) and is often accompanied by autonomic signs. Petit mal, or absence seizures are also generalized, but are rare in domestic pets. Petit mal seizures are characterized by a brief change in consciousness and are frequently unrecognized. Focal seizures are caused by a focal disruption of neuronal activity and historically have been associated with secondary epilepsy. However, more careful evaluation of the signs shown by dogs with presumed idiopathic epilepsy has revealed that many of these dogs have focal seizures. It is therefore becoming accepted that the presence of a focal seizure does not rule out primary epilepsy. The signs reflect the area of cortex that is affected, for example a lesion in the left motor cortex will produce twitching of the right side of the body, and a lesion in the visual cortex may produce fly biting. A lesion within the limbic system can produce disturbing alterations in behavior, screaming, viciousness, and somnolence. Previously known as psychomotor seizures, these are now called complex focal seizures. Focal seizures can generalize (spread to involve the whole cortex) producing more typical generalized seizures. Causes of Seizures Causes of seizures can be divided into intra- and extracranial categories (Table 1). Extra-cranial causes include metabolic problems (e.g. hypoglycemia, portosystemic shunt, electrolyte disturbances, hyperlipemia) and toxicity (e.g. lead, ethylene glycol). Intracranial causes include neoplasia, infectious/inflammatory disease, hydrocephalus, trauma, vascular disease, and primary epilepsy. Several different groups are now examining the canine genome in families of epileptic dogs to identify causative mutations. It is very likely that tests for carrier and affected status will be developed for familial (primary) epilepsy in the next decade. Table 1
Identification of Seizures Generalized seizures are usually easy for owners to recognize, but many 'episodes' can be more difficult to define, especially as they are rarely witnessed in the clinic. Useful questions to ask owners include whether the animal goes stiff (versus limp in syncopal episodes), falls over, loses consciousness, or develops autonomic signs (urination, defecation, salivation), and whether there are any pre- or post- seizure signs. Cats in particular can have unusual seizures in which autonomic signs (typically the cat develops hippus - spasmodic dilation and constriction of the pupil and salivation), or bizarre behavior (yowling, frantic running) predominate. Seizures are more likely to occur when the animal is resting in contrast to syncopal events so it is worth establishing when episodes occur from the owner. It is often useful to ask owners to video-tape episodes, and to get them to check a heart rate and mucous membrane color during an episode if you feel it might be syncopal. Dr O'Brien of the University of Missouri has authored an excellent web site complete with video clips of different seizures that may be useful for owners to review (http://www.canine-epilepsy.net/basics/basics_index.html) Diagnosis of Seizure Disorders The most effective seizure management is possible when a diagnosis has been made. The presenting signalment, history, and clinical signs allow prioritization of differential diagnoses and selection of appropriate diagnostic tests. When symptomatic or reactive epilepsy is suspected (e.g. a 12 year old golden retriever with new onset of seizures), a full diagnostic evaluation including a bile acid tolerance test, imaging of the brain, and analysis of cerebrospinal fluid should be recommended. In many cases, a full evaluation is not vital at first onset of seizures (e.g. a healthy 3-year-old German shepherd dog with recent onset of seizures), but a minimum data base, bile acid tolerance test and fundic exam is always recommended. The bile acid tolerance test not only rules out a portosystemic shunt, but also gives a baseline measure of liver function that can be referred to at a later date if the animal is placed on a hepatotoxic drug such as phenobarbital. All owners can be given a list of signs to watch for that might indicate an underlying brain disease (behavioral changes, stumbling, visual deficits) and therefore a need for a more complete diagnostic work-up. The most common presenting sign for a brain tumor is seizures, and this is frequently the only sign of the disease. It is extremely important to recommend brain imaging by computed tomography (CT) or magnetic resonance imaging (MRI) in any dog with new onset of seizures that is over 6 years of age. Certain breeds are predisposed to specific diseases and so the signalment will also guide the recommendations made. For example, new onset of seizures in a 4-year-old Boxer is more likely to be due to a brain tumor than primary epilepsy. Similarly, new onset of seizures in a 2-year-old pug is most likely a result of encephalitis. Cats are more prone to hypertension and its consequences than dogs, but in both species it is important to try to obtain a blood pressure measurement and to examine the retina for any evidence of vascular or other disease. When to Treat Seizures Most seizure disorders cause recurrent seizures that are progressive in nature because of gradual recruitment of additional neurons to seizure foci (kindling). If an underlying cause for the seizures can be identified, treatment should be directed at that cause. Use of anti-epileptic drugs is indicated when a diagnosis of primary epilepsy is made, or when treatment of the underlying cause of the seizures in secondary epilepsy does not control seizures (e.g. animals with brain tumors, hydrocephalus, or encephalitis). It is important to establish seizure frequency prior to initiating treatment as anti-epileptic drugs have side effects and may not be necessary. For example, if seizure treatment is initiated after the first seizure, it will never be clear whether this was going to be the only seizure the animal ever had, and it will be difficult to know whether to stop the medications or not. An exception to this guideline is when a diagnosis has been made and any further seizures could be life threatening. For example, if the animal has one seizure and a brain tumor is diagnosed, further seizures could cause fatal increases in intracranial pressure and the animal should be started on antiepileptic drugs immediately. A more general rule of thumb is that seizures should be treated when they occur more frequently than once a month, when they occur in clusters or are associated with status epilepticus, or when they are associated with unacceptable side effects (e.g. an extremely prolonged post seizure period, viciousness, or airway obstruction in brachycephalic breeds of dog). In all instances, the most effective treatment requires full owner understanding and compliance. It is important to determine each owner's expectations prior to initiating therapy. What Drugs to Use - Dogs In dogs the two main drugs used to treat seizures are phenobarbital and potassium bromide. Both drugs are effective when used alone and when used in combination. Primidone is not recommended because of hepatotoxicity, and oral diazepam is not an effective maintenance antiepileptic drug in dogs due to its short half-life. Phenobarbital has a half-life of 48 to 72 hours and should be administered orally twice a day. Starting dose is 2 - 4 mg/kg p.o. twice a day, and steady state is reached in 10 - 14 days. If rapid control of seizures is needed (for example, a dog presents with cluster seizures), administering 12 mg/kg split over 24 - 48 hours will achieve therapeutic blood levels of phenobarbital, although this will cause transient sedation. The advantages of phenobarbital include good efficacy, availability, reasonable cost, convenient dosing regime, and rapidity with which changes in dose are reflected in blood levels, making dose adjustment straightforward. Disadvantages include record keeping as it is a controlled drug, polyphagia, PUPD, initial sedation (should resolve in about one week), and sedation when higher blood levels are necessary, hepatotoxicity (most frequently associated with blood levels of greater than 35microg/ml) neutropenia and thrombocytopenia (a very rare complication), necrolytic dermatitis, and drug interactions (should not be used in conjunction with cimetidine, chloramphenicol, or ketoconazole). Tolerance to phenobarbital may develop, necessitating higher doses to maintain the same blood level over time. Therapeutic blood levels range from 15 - 45 microg/ml, although levels of greater than 35microg/ml are associated with an increased risk of hepatotoxocity. Once steady state is reached, changes in dose to achieve a desired blood level can be calculated using the following equation: New dose = current dose X desired blood level/measured blood level. The dose required is dictated by:
Potassium bromide has been used with great success as an addition to phenobarbital therapy in dogs with refractory seizures. It is now increasingly being used as a single agent in dogs. Potassium bromide has a long half-life ranging from 24 - 46 days in dogs depending on the dietary salt content and renal function. It should be dosed once a day at a rate of 25 - 40mg/kg/day and steady state is reached in 3 - 4 months. In order to achieve therapeutic blood levels (100 - 300mg/dl) more quickly, it can be loaded by dosing at a rate of 100-130mg/kg/day for 5 days, then decreasing the dose to the maintenance of 30mg/kg. The blood level should be checked after the 5-day loading dose and again 4 - 6 weeks later to ensure that therapeutic levels are maintained. In case of emergency, therapeutic levels can be achieved in one day by oral administration of 200mg/kg with a little food 3 times at 2 - 3 hour intervals (total dose of 600mg/kg). The advantages of potassium bromide include good efficacy particularly when used in addition to phenobarbital therapy, lack of hepatotoxicity, once daily dosing, reasonable cost and lack of controlled drug status. Disadvantages include PUPD and polyphagia, sedation, and hind limb weakness when at high blood levels (particularly in combination with phenobarbital), lack of approval for veterinary use, need for a consistent diet (changes in salt content of the diet change drug blood levels), gastrointestinal irritation, a skin condition called bromoderma, and possibly an association with hyperlipemia and pancreatitis. Potassium bromide is available in liquid and capsular forms. Capsules are said to be associated with a higher frequency of gastrointestinal side effects as the dissolving capsule provides a focus of the salt solution within the stomach. Gastrointestinal irritation can be minimized by administering the drug with food. When deciding whether to start treatment with phenobarbital or potassium bromide or a combination of both drugs, a number of factors can be considered. For example, if the dog is very young, it might be desirable to start treatment with potassium bromide and only add in phenobarbital if necessary to minimize the time the dog may be receiving a hepatotoxic drug. In animals presenting with a severe cluster of seizures, it is usually preferable to start immediate treatment with phenobarbital, because steady state blood levels can be reached more quickly and the drug can be administered intravenously. If it is not possible for the owner to administer a drug every 12 hours, potassium bromide may be the drug of choice because it can be administered every 24 hours. Finally, drug side effects should be taken into account and dogs with liver disease should not be treated with phenobarbital, while it may be advisable to avoid potassium bromide in dogs with a history of pancreatitis. Managing the Chronic Epileptic Dog Following initiation of treatment, the owners should be asked to keep a log of seizures including a description of the event and post seizure signs. Blood levels of the drug used should be measured after starting treatment (10-14 days for phenobarbital, 3 - 4 months for potassium bromide unless a loading dose was used). At that time the severity of side effects can be assessed. If seizure frequency is greater than one a month (or severe clusters etc as discussed above), then the first thing to do is measure blood levels of the drug and evaluate the dog to ensure that no additional neurological signs have developed, indicating a different underlying problem. To address the increased seizure frequency, the dose of the antiepileptic drug being administered can be increased in direct proportion to the desired increase in blood level. Alternatively, a second drug can be added into the treatment protocol (either phenobarbital or potassium bromide). Typically, the author will make sure the blood level of phenobarbital is between 25 and 30 microg/ml and potassium bromide is greater than 150mg/dl prior to adding in a second drug. However, in some cases there may be a good reason to add in a second drug without having attained these blood levels. For example, if the animal is showing signs of liver disease, potassium bromide should be added in as soon as possible to minimize the dose of phenobarbital necessary. When seizure frequency is not adequately controlled by the above drugs, or unacceptable side effects occur, effective seizure treatment becomes problematic and expensive. Felbamate (Felbatol), gabapentin (Neurontin), levatiracetam (Keppra) or zonisamide (Zonegran) can be added to potassium bromide and phenobarbital. Their efficacy has not been tested objectively as yet, and the relatively limited number of dogs treated so far means that we are still learning about all the side effects and beneficial effects of these drugs. What Drug to Use: Cats Epileptic cats are not uncommon and pose unique therapeutic challenges when attempting chronic treatment. For example, cats can be extremely difficult for owners to pill. It is also important to remember that primary epilepsy is less common in cats than in dogs, and an underlying cause for their seizures should always be sought. Phenobarbital and potassium bromide can be used as antiepileptic drugs in cats. In addition, benzodiazepines can be used orally in this species. Phenobarbital can be used as an effective anti-epileptic drug in cats. The dose rate used and blood levels desired are similar to dogs, but there are some specific side effects that may be seen. Phenobarbital has been associated with greater sedation in cats than dogs, therefore the therapeutic blood level range is 10-30microg/ml and the initial dose rate is 1 - 2 mg/kg/q12-24 hours. The author usually doses them twice a day, but in some cats once daily dosing at night will suffice. Polyphagia, PUPD, blood dyscrasia, dermatitis and unusual behavior can all occur. Severe hepatotoxicity has not been reported in cats, but this may simply reflect the fact that far fewer cats receive chronic phenobarbital therapy. Cats' hepatic function should therefore be monitored in the same way as dogs on phenobarbital, with blood levels and hepatic function checked every 6 -12 months. Potassium bromide has a shorter half-life in cats than in dogs: a dose rate of 30mg/kg/day achieved steady state in 5 weeks and therapeutic blood levels within 2 weeks. However, in the same study, seizures were only controlled in 7 of 15 cats, and half the cats developed adverse side effects, the most common of which was a cough. This is thought to result from secretion of bromide into the airways, causing irritation. Although this was initially described as asthma, and seems more common in cats with previously diagnosed reactive airways, it is not responsive to glucocorticoid therapy and can only be treated by withdrawal of the drug. As a result of these problems, potassium bromide is not recommended as a first line of therapy in cats. Status Epilepticus Status epilepticus is an emergency that every practice will have to deal with at some time or other. Management of such cases is enhanced by having an emergency protocol ready at hand and by having intravenous phenobarbital available. Although there are many different drug doses cited and each case needs to be managed differently, a suggested flow sheet is provided below:
Assessing the Comatose Patient Intracranial Pressure (ICP) (normal - <10mmHg) and Perfusion of the Brain Skull contains 1) brain (80%), 2) CSF (10%), 3) blood (10%). An increase in any of these 3 components will result in an increase in ICP. The brain needs a regular supply of blood (perfusion) in order to function, and unfortunately if ICP increases, it can decrease the perfusion of the brain. Normal perfusion of brain : CPP = ABP - ICP CPP - cerebral perfusion pressure, ABP - arterial blood pressure As ICP increases, first CSF is displaced into the foramen magnum (production rate is not affected acutely), then cerebral perfusion decreases and ultimately the brain can herniate, causing death. There are several types of brain herniation, but the first 2 are the most common and important:
How to assess comatose animals Parameters to evaluate:
Normal management of comatose patients with suspected increased or increasing ICP is to
Mannitol is a potent diuretic agent that will rapidly reduce the ICP although this effect is not long term and an accurate diagnosis of the underlying problem should be pursued. Mannitol should only be used when absolutely indicated because it can causes severe dehydration. We use it:
0.5 - 2.2g/kg at the first dose over 5 - 15 minutes. Too rapid an infusion causes an initial increase in ICP. Many people recommend following this with 0.7mg/kg furosemide iv 15 minutes later to help prolong the osmotic gradient created by mannitol. Following this discontinue fluids for 2 hours ad then restart at about 80% maintenance rate. Summary Patients that are comatose or recovering from status epilepticus need to be watched very closely for evidence of deterioration. In both situations, the underlying cause of the problem should be diagnosed and treated promptly. Management of status epilepticus and coma simply means that you are managing the clinical signs, not the cause. When assessing parameters such as papillary light responses, remember that certain drugs will affect these (e.g. atropine will cause fixed dilated pupils). Careful nursing of a severely affected neurological patient can be very rewarding because some dramatic recoveries can be obtained. |
