pets disease

The vestibular system is a specialized portion of the nervous system found within the inner ear, brain, and spinal cord. Its duty is to maintain a state of equilibrium and balance. By communicating with the nerves supplying the eyes, limbs, and trunk, the body is able to coordinate the position and activity of these regions with movements of the head.
Peripheral vestibular dysfunction (PVD) is a disease that affects the nerves of the vestibular apparatus in the ears. PVD is characterized by a sudden onset of incoordination and loss of balance, which is often accompanied by a head tilt, involuntary twitching of the eyeballs, and in many cases, vomiting. The causes of this disorder can include trauma to the ears, skull infections, and tumors involving the middle or inner ear. Diagnosis of PVD is achieved using clinical signs and various laboratory tests to rule out other potential causes of the symptoms. Radiographs of the skull may be helpful in the detection of any masses or infections that may involve the inner portions of the ears. Treatment, of course, depends on the underlying cause and usually includes high doses of corticosteroid medications designed to reduce inflammation involving the vestibular apparatus.
Vestibular ataxia syndrome is seen in kittens born of queens stricken with feline parvovirus during pregnancy. Owners often are alerted to a problem when these kittens seem to have trouble in attempting to walk. The condition will not improve as these kittens mature, nor will it usually worsen.
Congenital vestibular syndrome is seen in Siamese and Burmese cats, with signs appearing anywhere from 2 to 4 weeks of age. Many of the Siamese cats affected are deaf as well. The prognosis for Siamese cats with congenital vestibular syndrome is good, with clinical signs usually abating by the time the cat is 6 months of age. In Burmese cats, however, the prognosis is not as good, and the poor quality of life for most of these individuals will usually warrant euthanasia.

Problems with Degenerative disk disease (DDD) can show up in smaller breeds as early as 3 years of age. In larger dogs, the onset of signs might not occur until they are 6 to 7 years old. Overweight dogs are at an especially high risk of developing complications associated with intervertebral disk disease.
The clinical signs seen with degenerative disk disease and/or disk rupture depend on the location of the lesion and the amount, if any, of the rupture that has taken place. In fact, the extent of pressure or damage to the spinal cord can be estimated according to the signs seen.
Dogs with early or mild cases of disk disease causing slight pressure upon the cord will be quite painful and reluctant to move. Many will cry or yelp when picked up. If the neck is involved, any manipulations attempted will be met with vigorous protests. These pets often prefer not to be bothered, and have the tendency to isolate themselves. Appetites are usually reduced as well. Since nerve fibers responsible for coordinated muscle movement run within the outer layers of the spinal cord, owners may also notice weakness and/or incoordination when their pet attempts to walk.
With more severe disk ruptures, damage to the deeper portions of the spinal cord can become a serious factor. When this occurs, partial or complete paralysis of one or more limbs might result, depending on the location of the rupture. If the entire depth of the spinal cord is involved, these animals will also lose all pain sensation to one or all four limbs, again depending on the areas of the spinal cord involved. Such severe cases carry a very grave prognosis, since treatment at this stage is rarely successful.
In most cases, confirmation of a ruptured disk is made via a thorough examination, clinical signs, and with radiographs of the vertebral column. If the exact location of the spinal lesion cannot be pinpointed with regular radiographs, a special test, called a myelogram, is performed. This test involves injecting a dye directly into the spinal canal. The dye, which can be identified on a radiograph, helps outline the cord lesion and demonstrate the extent of the disk rupture.
The type of treatment instituted for disk disease and/or rupture depends on the extent of the damage done by the disk to the spinal cord.
For those dogs showing only pain with some mild incoordination, a strict 2 week confinement period, either at home or in a hospital setting, is a must Afterward, short 10- to 15-minute physical therapy sessions, including swimming, can be performed twice daily to help speed recovery and return to normal function.
For cases in which the affected dog is having great difficulty walking, strict cage confinement combined with anti-inflammatory therapy and other specific treatment is indicated. If the disease is such that the dog is unable to support weight on the limbs at all, even after medical therapy, then surgery is required to reduce the pres- sure placed on the spinal cord by the ruptured disk.
This surgery, called a laminectomy or hemilaminectomy, works best if performed within the first 24 hours of the injury. It involves the removal of part of the vertebra over the affected cord segment. By eliminating the enclosed space through which the spinal cord runs, the pressure on the cord caused by the inflammation is allowed to dissipate. At the same time, surgeons often elect to perform intervertebral disk fenestrations, aimed at removing the offending nucleus pulposus from the disk in question and from adjacent disks as well.
The prognosis is poor for those pets that are unable to walk and have lost deep pain sensation in their legs as a result of a ruptured disk. The loss of deep pain indicates that the entire depth of the spinal cord is invariably involved, and surgical salvage procedures are rarely successful.
In those instances where surgery is unsuccessful, or in which paralysis is permanent, euthanasia is not always the only option left to the owner. Special “wheelchairs” for dogs have been developed for dogs paralyzed by a ruptured disk or other neurological accidents. Although not suitable for every patient, these carts can help afford mobility to select patients willing to wear the apparatus and an alternative for those owners willing to devote much time and care to their paralyzed pet. If you think that such a device could be applicable to your own pet’s situation, ask your veterinarian for more details regarding this and other management options available.
There are specific measures that pet owners can take to help protect their dog from a ruptured disk. The first and most important is to prevent obesity. Overweight dogs are prime candidates for such complications; hence, they should be placed on a strict diet to reduce this risk factor.
Jumping should be discouraged in dogs predisposed to intervertebral disk disease. Many ruptured disks result from pets jumping off and on furniture. Pets so inclined should be assisted up or down whenever possible. Even better, a small chair or ramp can be placed in front of the dog’s favorite piece of furniture to allow easier access.
Whenever lifting a dog with back problems, be sure to firmly sup- port both the front and hind ends, keeping the back as straight as possible. This stabilizes the position of the spine and affords the handler with better and safer control should the pet struggle.
Surgical intervertebral disk fenestration is often used as preventive measures in dogs that have previously suffered from bouts of inter- vertebral disk disease. As mentioned before, this involves the penetration and removal of the nucleus pulposus from one or more intervertebral disks suspected of causing current or future problems. If this is done, the danger associated with later disk rupture is removed with the nucleus.

Coursing along the length of the back, the spinal cord travels protected within the bony vertebral column. Separating each vertebra, and located beneath the spinal cord itself, are structures called intervertebral disks, which serve as cushions between each individual vertebra, absorbing shock and forming joints that allow the vertebral column to bend. Each circular disk is composed of an outer band of tough, fibrous tissue called the annulus fibrosus surrounding an inner gelatinous center called the nucleus pulposus. This latter structure is responsible for absorbing any shock placed on the disk.
Degenerative disk disease (DDD) is characterized by the slow degeneration of the nucleus pulposus within one or more intervertebral disks. As these continue to degenerate, they become less resilient and can even calcify, leaving the intervertebral disk without its shock-absorbing unit. As a result, the disks so affected become very susceptible to compression damage, even from normal day-to-day activity. In pets so affected, continued stress or sudden trauma to the disk or vertebral column can lead to an overt tearing or rupture of the annulus fibrosus, and extrusion of the degenerating nucleus pulposus. Unfortunately, since the top portion of the annulus is much narrower than the bottom portion, this extrusion usually occurs upward directly into the spinal canal, damaging the spinal cord and associated nerves.
Overt disk ruptures may be classified as partial or complete. In partial ruptures, the annulus can either be stretched or displaced into the spinal canal, or it can partially rupture, allowing a small amount of the nucleus within to escape and pressure the spinal cord. With complete ruptures, the entire nucleus content is allowed to escape into the spinal canal. Obviously, the consequences of such a rupture versus a partial one are much more severe.
The region of the vertebral column most susceptible to rupture is that portion extending from the last rib to the pelvis. The neck region is another area that can be affected. In a pet suffering from Degenerative disk disease (DDD), even the slightest wrong move, such as jumping off the couch or running too fast, can cause an affected disk to rupture. Dogs are the species primarily afflicted with Degenerative disk disease (DDD). Although any dog can suffer from DDD, there do seem to be some breed dispositions. The dachshund breed certainly leads the list in the number of cases reported. Other breeds commonly afflicted with degenerative disk disease include poodles, Pekingese, and Lhasa apsos. Beagles and cocker spaniels also have a notable incidence of Degenerative disk disease (DDD) in their neck region.

Myelopathies are degenerative diseases that strike the spinal cord and nerve fibers coursing throughout the body. These diseases involve the gradual loss of the outer, conductive coating that surrounds certain nerve fibers, called myelin. This loss impairs the fiber’s ability to transmit nerve impulses. Seen primarily in older, larger breeds of dogs, especially German shepherds, Myelopathies are characterized by muscular incoordination, weakness, and atrophy. As the nerves innervating the hind legs are affected, a turning under or dragging of the hind feet may result. In fact, the hind limb weakness exhibited by some dogs with degenerative myelopathy is often mistaken for arthritis of the hips or spondylosis deformans of the spine. However, pain is rarely a factor in this disease.
A myelopathy is tentatively diagnosed using historical findings, clinical signs, and reflex testing. Dogs afflicted with this condition will exhibit weak to absent reflex activity in their limbs. Electromyograms (EMGs) may be performed as well to evaluate electrical activity associated with the muscle tissue of the body. Unfortunately, because an exact cause of most Myelopathies, other than genetics, remains a mystery, there is no effective treatment to date. Vitamin therapy has been used in some instances to slow the progression of the disease, yet motor incapacitation is inevitable.

Seen primarily in Great Danes and Doberman pinschers, vertebral instability is characterized by instability and deformities in the vertebra of the neck region, leading to pressure on the spinal cord in that region. The condition in these breeds is hereditary in nature; however, trauma can predispose any dog to canine wobbler syndrome. Signs associated with vertebral instability include incoordination, weakness, and paralysis. Pain is rarely a feature of this disease. Diagnosis of vertebral instability is made with radiographic X rays. Treatment involves the use of anti-inflammatory medication to reduce the spinal cord inflammation. Surgical decompression of the spinal cord is also warranted in severe cases.

Paralysis can be defined as a disruption of the nervous system leading to an impairment of motor function and/or feeling to a particular region or regions of the body. This impairment can be in the form of a spasticity of the muscles in the involved region, or these muscles may become completely limp. In either case, the muscles involved are unable to function in the manner in which they were intended.
Paralysis involving the sensory portion of the nervous system can result in an increased sensitivity to pain or in a complete absence of it. Finally, paralysis resulting in the inefficient function of certain internal organs can occur as well if the nerves supplying these structures are disrupted in any way.
Any disease or disorder that traumatizes the brain, spinal cord, and nerves has the potential to cause paralysis. In dogs and cats, some of the more common causes seen by veterinarians include infectious diseases and parasites, being hit by a car, ruptured disks, and in the case of facial muscle paralysis, ear infections.
Treatment of paralysis is geared toward identifying and treating the underlying cause. If it has been caused by trauma, anti-inflammatory agents combined with drugs designed to draw fluid out of the central nervous system might help reverse signs of paralysis, yet their usefulness is dependent on the extent of the nervous injury and how quickly therapy is instituted.
Pets that have sensory paralysis in a limb might require limb amputation to prevent self-mutilation of the leg. In instances where an irreversible paralysis involves more than one limb, or involves the malfunction of internal organs, pet owners must seriously consider not only their pet’s quality of life as a paralytic but their own as well, before prolonged therapeutic or rehabilitative measures are undertaken.

The Nervous System
The nervous system involves a complex interaction between special elements designed to originate or carry unique electrochemical charges to and from the various organs within the body. Like its endocrine counterpart, the nervous system initiates and regulates bodily functions and ensures its owner of awareness to the surrounding environment.
Anatomy and Physiology
The smallest component of the nervous system is the neuron. There are over 10 billion of these dynamic cells in the body, and they have the ability to originate and propagate nerve impulses. These result from changes in electrolyte ratios, namely, those of sodium and potassium, occurring across the cell membrane of the neuron. For this reason, abnormalities in the amounts of sodium and potassium within the body can have devastating effects on nervous system function.
Generated impulses are transmitted to their respective targets along special cellular projections, originating from the cell body, called nerve fibers. Speeds of transmission along these nerve fibers can reach over 110 meters per second. Groups or bundles of fibers coursing together are what are referred to as nerves.
Within the nervous system, neurons can link together to form a continuous chain to allow for the uninterrupted passage of a nerve impulse to its desired destination. A synapse is described as this connection between two nerve cells. Special chemical transmitters located at synapses (neurotransmitters) transfer the impulses from the end of one neuron to the receptive end of another, allowing the impulse to continue in its travels. Neurotransmitters are also found at the junctions between nerve fibers and their target muscles or organs. In dogs and cats, organophosphate insecticide poisoning exerts its deadly effects by interfering with the normal breakdown of acetylcholine, one of these neurotransmitters.
The brain is the control center for the entire nervous system. Internally, it is composed of gray matter, which is a collection of neuron cell bodies and synapses between nerve cells, and white matter, made up of nerve fibers originating from the neuron cell bodies.
The mammalian brain is divided into three divisions: the cerebrum, the cerebellum, and the brainstem. The largest of the three, the cerebrum, is responsible for memory, sensory awareness, learning, and muscular movement. The cerebellum, located in back of and just beneath the cerebrum, functions to coordinate muscular activity and movement, and control body posture. The final division of the brain, the brainstem, serves a variety of functions. It acts as an important intermediary by relaying messages between the cerebrum, cerebellum, and the spinal cord, and influencing activities such as heartbeat, breathing, vision, and hearing. A special portion of the brainstem, called the hypothalamus, provides an important link between the nervous system and the endocrine system.
The spinal cord is the major highway of activity for the transmission of nerve impulses between the brain and the rest of the body. It runs along the course of the back within the spinal canal formed by the vertebral column. Like the brain, the spinal cord also contains gray matter and white matter. Large spinal nerves containing numerous smaller nerve fibers branch off from the main cord along its course and travel to respective target muscles and organs. The spinal cord can also serve as coordinating center for certain reflex activities involving the muscles of the limbs without first requiring a nerve impulse to be sent to the brain. Clinicians can often assess the extent of damage to a spinal cord by evaluating these spinal reflex arcs.
Spinal nerves branching off from the spinal cord contain two main types of nerve fibers: somatic nerve fibers, which carry information to and from skeletal muscle, skin, joints, and appendages (effects such as muscle contraction, produced by somatic fibers, are said to be under conscious or voluntary control from the brain), and autonomic nerve fibers, which innervate glands and internal organs throughout the body. Unlike somatic nerves, autonomic nerves act mainly on reflex, with little voluntary control. Blood pressure, cardiac output, breathing, gastrointestinal motility, body temperature, and hormone secretion are only some of the many vital life functions under the influence of this unique system.
Three thin layers of tissue called meninges cover both the brain and the spinal cord. Between these layers is found a special type of fluid, called cerebrospinal fluid. Meninges with their accompanying cerebrospinal fluid serve to protect, support, and nourish the underlying nervous tissue. Abnormal increases in the amount of cerebrospinal fluid can cause serious damage to the spinal cord and brain. Hydrocephalus is the term used to describe such a condition affecting the brain.

Feline ischemic encephalopathy (FIE) is a neurologic condition that has been known to strike cats. FIE is caused by a sudden disruption of blood supply to the brain, similar to a stroke in humans. Although a definitive cause has yet to be determined, cardiomyopathy, neoplasia metastasis, and even feline heartworms are suspect. Affected cats exhibit marked depression, incoordination, circling behavior, and/or seizure activity. The pupils of the eyes may become dilated, and blindness may be apparent. Acute clinical signs usually resolve within 7 to 10 days; however, residual neurologic deficits of varying degrees often remain indefinitely.
Diagnosis of feline ischemic encephalopathy is based on history and clinical signs seen, as well as ruling out other causes of similar symptoms, such as vestibular disease, feline leukemia, and poisonings. Treatment of this neurologic disorder involves the administration of high doses of anti-inflammatory medications. In addition, medications designed to dilate the brain’s blood vessels and thin the blood may be employed in an effort to improve overall circulation to the affected regions of the brain.
The prognosis for survival in cats with FIE is guarded during the first 48 hours following onset of clinical signs. After 48 hours, the prognosis for survival is good, since FIE is a no progressive disorder.

Feline hyperesthesia syndrome (“twitchy skin syndrome”) is a condition characterized by some unique clinical signs. Affected cats exhibit a rippling of the skin on their backs, especially when petted in the lower back region. They might chew or lick at their tail incessantly, and appear to be “spaced out,” spontaneously darting throughout a room or house and attacking objects and owners without provocation.
The exact cause of this condition remains unknown. Some researchers feel that it is a form of epilepsy. Because “emotional” breeds such as Siamese, Persians, and Himalayans seem to be most often affected, other researchers believe that it is actually a behavioral disorder brought about by an upsetting experience or circumstance. Even food preservatives used in cat foods have been accused of causing feline hyperesthesia syndrome.
Medical therapy for this disorder consists of the use of ant anxiety medications or sedatives in an attempt to modify the cat’s behavior. Identifying and correcting any environmental upsets (including any dietary changes) that might have a possible link to the problem are needed as well.

Those who own a pet that has suffered from seizures know firsthand how scary these episodes can be. A seizure is defined as uncontrolled label behavior or muscle activity caused by an abnormal increase in the brain’s nervous activities. Epilepsy is a term used to describe recurring seizures.
Seizural activity in dogs and cats can be quite obvious or quite subtle. In essence, seizures should be suspected anytime that a pet under- goes sporadic, unexplained behavioral changes.
What causes seizures in dogs and cats? Potential causes are numerous and include viral infections (e.g., distemper, FIP), toxoplasmosis, fungal infections (e.g., cryptococcosis), epilepsy, hydrocephalus, brain tumor, intestinal parasites, low blood sugar, low blood calcium, insecticide poisoning, and heat stroke. Sometimes the cause cannot be determined; if so, seizure episodes are termed “idiopathic.”
Because causes of seizures are so numerous, a thorough examination and blood workup by a veterinarian is warranted whenever a pet exhibits seizures. In some cases, managing or eliminating an underlying cause will eliminate the seizures. In others, such as with idiopathic epilepsy, there is no known cause, yet by ruling out the other potential causes (e.g., hydrocephalus; see Fig. 17.1) and establishing a pattern of occurrence, most cases can be effectively managed with anticonvulsant medications. With idiopathic epilepsy, seizures can begin at any stage in life, yet, for the most part, they begin around 1 to 3 years of age. While the cause of idiopathic epilepsy is unknown, it has been shown to be inheritable in some dog breeds, including beagles and dachshunds.
Seizures themselves are rarely life-threatening, unless some physical harm comes to the pet as a result of the fit. The typical seizure or epileptic fit has three stages, or phases. The first of these, the preictal phase, is marked by anxiety and restlessness on the part of the pet. The actual period of the seizure activity, ictus, follows next. Its duration might be for only a few seconds or it might be minutes. Certainly the longer the seizure lasts, the more dangerous it is to the health of the pet. The postictal phase following the seizure is characterized by an overall depression or confusion. Postictal pets can appear to be blind, running into walls and objects, or they might just sleep a lot. This phase can last for a few hours or for days, with the pet returning to its normal state after its conclusion.
There is one Seizural presentation called status epilepticus that can prove fatal to a pet. This condition is characterized by a cluster of seizure events occurring in quick succession. Unless appropriate emergency medication is administered intravenously to stop the seizures, these dogs and cats can lapse into a coma and die. As a result, prompt recognition and action on the part of the pet owner is essential.
When attempting to diagnose the cause of Seizural activity, veterinarians will first look at the age and the type of pet involved. For example, seizures occurring in pets under 1 year of age commonly result from birth defects or from infectious diseases, such as canine distemper or intestinal parasites, whereas seizures occurring in a very old dog or cat often indicate kidney failure or cancer. In smaller, toy puppies and in active hunting dogs, low blood sugar brought on by illness, stress, or overexertion can be an important inciting cause. Seizures occurring in a pregnant dog or cat or one that has just given birth are usually caused by “milk fever,” or low blood calcium. Finally, as mentioned above, certain breeds are prone to idiopathic epilepsy.
A good history is also vital to help determine the cause of the seizures. Does the pet have access to any type of poison? Has the pet ever suffered any type of physical trauma, such as being hit by a car? Has the intensity of the seizures gradually been getting worse or increasing in frequency? The answers to these and other questions can help a veterinarian narrow the choices.
A complete blood profile and urinalysis should be performed to help rule out the metabolic and infectious causes of seizures. Radiographs and ultrasound can prove to be helpful in certain instances as well. If no underlying cause can be found, and the history supports it, a diagnosis of idiopathic epilepsy is made and treatment is started on this premise.
For cases other than idiopathic epilepsy, treatment is geared toward correcting or managing the underlying problem, whether it is kidney failure, poisoning, low blood sugar, or another condition. In instances in which idiopathic epilepsy is suspect, anticonvulsant medications can be used to control or even eliminate the Seizural activity.
Determining the exact dosages of anticonvulsant medications might require frequent adjustments at the start in order to accommodate the pet’s individual needs. Pets on anticonvulsant medication may need liver function tests performed annually, since some of these medications can damage the liver over the long term.