 The brain comprises the cerebrum, cerebellum,
midbrain and brain stem. The cerebrum is the largest part of the brain and is the center of learning, memory, sensory input,
behavior and voluntary movement. Diseases affecting the cerebrum are characterized by depression, alterations in personality,
behavior and seizures. The cerebellum has two lobes. Its primary functions are to integrate motor pathways, coordinate movements,
and maintain balance. Diseases of the cerebellum result in lack of coordination, unstable gait, and muscle tremors.
In the midbrain and brain stem are the centers that control the respiratory rate, heartbeat, blood pressure and other vital
functions. At the base of the brain and closely connected to the midbrain and brain stem are the hypothalamus and pituitary
glands. These structures are important in regulating the dog's body temperature and hormone systems. They are also the
centers for primitive responses such as hunger, thirst, anger and fright. The spinal cord passes down a bony canal formed
by the arches of the vertebrae. The cord sends out nerve roots that combine with one another to form the peripheral nerves.
Diseases of the spinal cord produce varying degrees of weakness and paralysis. The cauda equina is the termination of
the spinal cord. Diseases of the cauda equina can produce paralysis of the tail, loss of bladder and bowel control and paralysis
of the anal sphincter. The paired cranial nerves, 12 total, arise from the midbrain and brain stem and pass directly
out into the head and neck through openings in the skull. The optic nerves to the eyes, the otic nerves to the ears, and the
olfactory nerves to the nasal cavity are examples of paired cranial nerves.
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Neurological Evaluation A complete health history is of paramount importance in diagnosing unexplained neurological symptoms. Your trained
professional (doggy doctor) will want to know if the dog has been in an
accident. Did he receive a blow to the head? Is he taking any medications? Has he been exposed to other dogs who exhibit similar
signs? Could he have gotten into any toxic substances? When did you first notice the symptoms? Did they come on suddenly or
gradually? Have they progressed? If so, has the progression been rapid or gradual? The age, sex and breed of the dog are important,
because some neurological diseases are genetically determined and appear in certain breeds or at certain ages. Special
tests are used in addition to a standard physical examination for a dog with a possible neurological problem. Your trained
professional (doggy doctor) will manipulate your dog to check her balance,
motor control and sensory perceptions. Diagnostic tests used in evaluating neurological function include X-rays of the
skull and vertebral column, electroencephalography (EEG), and muscle
and nerve conduction studies. A spinal tap is a procedure in which a needle is inserted into the spinal canal to remove cerebrospinal
fluid for laboratory analysis. A myelogram is a spinal tap in which dye is introduced into the spinal canal so signs of spinal
cord compression will be visible on X-rays. Computer-assisted tomography (CAT scan) and magnetic resonance imaging (MRI) enable a radiologist
to see a computerized image of the structures in the brain, spinal canal, and body cavities. Head Injuries A dog's head can be injured in many ways, including a car
accident, a fall, a blow to the head or a gunshot wound. Since the brain is encased in bone and surrounded by a layer of fluid,
it takes a major blow to the head to fracture the skull and injure the brain. Skull Fractures A skull fracture can be linear, star shaped, compound (compound fracture opens to outside the body), or depressed (forming a depression). Skull fractures often extend into the middle ear, nasal cavity, or sinuses, creating pathways
for bacteria to gain access to the brain and cause infection. In general, the larger the skull fracture, the greater the likelihood
of brain injury. However, the brain can be injured even if the skull is not broken. Open Fontanel The skull is formed by three bone plates, and the area at the top of the skull where they come
together is called the fontanel. Usually these plates fuse when a puppy is about 4 weeks old, but sometimes they never completely
fuse, leaving a hole at the top of the skull called an open fontanel, or molera. The open area can range in size from a 50
cent piece to a penny. Most of the time an open fontanel will close over by the time the dog is 1 year of age, but sometimes
it will remain open throughout the dog's lifetime. These areas can be susceptible to trauma but are generally not
a problem. In some dogs this condition may be associated with hydrocephalus. Congenital open fontanel is seen primarily
in Chihuahuas, but the condition can be found in all the toy breeds. Since it's likely a hereditary problem, dogs with
an open fontanel should not be bred. Brain Injuries Injuries severe enough to
fracture the skull are often associated with bleeding into, and around the brain. Brain injuries are classified according
to the severity of brain damage. Contusion (Bruising) With a contusion, there is no loss of consciousness. After a blow
to the head, the dog remains dazed, wobbly and disoriented. The condition clears gradually. Concussion By definition, a concussion means the dog was knocked unconscious. With a mild concussion there is
only a brief loss of consciousness, while with a severe concussion, the dog may be unconscious for hours or even days. When
he returns to consciousness, the dog exhibits the same signs as for a contusion. A severe concussion causes the death
of millions of neurons. Recent information indicates that brain cell death does not cease within a few hours of the injury,
but can continue for weeks or months. Seizures Seizures can occur at the time
of injury or at any time thereafter. Seizures at the time of injury are particularly detrimental because they increase pressure
in the skull and compromise blood flow. This worsens the effects of the injury. Seizures that occur weeks after the injury
are caused by scars that form in areas where brain tissue has died. Brain Swelling and Bleeding Severe head
injuries result in brain swelling and bleeding into and around the brain. Brain swelling, technically called cerebral edema,
is always accompanied by a depressed level of consciousness and often coma. Since the brain is encased in a rigid skull, as
the brain swells the cerebellum is slowly forced down through the large opening at the base of the skull. This squeezes and
compresses the vital centers in the midbrain . Death occurs from cardiac and respiratory arrest. Blood clots can
form between the skull and the brain or within the brain itself. A blood clot produces localized pressure that does not, at
least initially, compress the vital centers. Like cerebral edema, the first indication is a depressed level of consciousness.
One pupil may be dilated and unresponsive to a light shined in the eye. Another sign is weakness or paralysis involving one
or more limbs. Brain Diseases Encephalitis (Brain Infection) Encephalitis is an inflammation of the brain. Symptoms include
fever, depression, behavior and personality changes (especially aggression),
uncoordinated gait, seizures, stupor and coma. Canine Distemper Canine distemper is the
most common cause of encephalitis in dogs. Signs develop two to three weeks after the onset of the disease. Other causes of
viral encephalitis include rabies, pseudorabies and herpesvirus. Rabies is a very serious disease, but with present-day remedies
the disease is not common among domestic animals. Canine herpesvirus produces encephalitis in puppies younger than 2 weeks
of age. Bacterial Encephalitis Bacterial Encephalitis is caused by organisms that enter the brain
via the circulatory system, such as endocarditis or by direct extension from an infected sinus, nasal passage or an abscess
in the head or neck. Migrating foreign bodies such as porcupine quills or grass awns may get into the central nervous system.
Fungal brain infections (caused
by cryptopococcosis, blastomycosis or histoplasmosis) are rare causes of encephalitis, as are protozoan infections. Tick-bourne rickettial diseases, notably Rocky
Mountain spotted fever and canine ehrlichiosis are frequent causes. These diseases may also involve the spinal cord. Postvaccination Encephalitis Postvaccination encephalitis is rare with modern vaccines. It was most likely to occur
when modified live virus distemper vaccine was administered at the same time as modified live parovirus vaccine in puppies
less than 6 to 8 weeks old. Lead Encephalitis Lead Encephalitis is seen primarily in young dogs who chew on materials that contain
lead, such as paint and drywall, especially in older buildings. Lead alters brain metabolism and causes inflammation and swelling.
Central nervous system signs are often preceded by vomiting, diarrhea or constipation. The diagnosis is confirmed by an elevated
blood lead level. Meningitis Meningitis is an infection of the surface of the brain and spinal canal. It is caused
by infected bite wounds about the head and neck and bacterial infections that travel to the brain from the sinuses,
nasal passages or middle ears. Aseptic meningitis is a non-bacterial disease of an unknown cause. It affects large breed dogs
4 to 24 months of age. The diagnosis of encephalitis or meningitis is based on analysis of cerebrospinal fluid obtained by
spinal tap. Serologic tests may identify the cause the of inflammation.
Granulomatous Meningoencephalitis This common inflammatory brain disease in dogs
is abbreviated GME. The cause is unknown. Female dogs of small breeds, especially terriers, Dachshunds, Poodles and Poodle
crosses, are predisposed. Although GME can occur at any age, most affected are 2 to 6 years of age. A chronic form of GME
called Pug encephalitis occurs as a inherited disease in Pugs between the ages of nine months and 4 years old. It often begins
with seizures, confusion and loss of memory. This form of the disease has also been seen in Yorkshire Terriers and Maltese. GME
can affect all parts of the brain (the
disseminated form) or only
specific areas (the focal form). There is a rare ocular form that targets
the optic nerves of the eyes. The disseminated disease appears suddenly and progresses over a matter of weeks. It is characterized
by incoordination, stumbling, falling, head tilt, seizures, circling and dementia. The focal disease begins with symptoms
such as those of a brain tumor. Behavior and personality changes may predominate. The focal disease progresses to the disseminated
disease over a period of 3 to 6 months. The ocular disease is characterized by sudden blindness with a dilated pupil.
It progresses to the disseminated disease more slowly than does the focal disease. GME can be suspected when a toy dog
such as a Poodle inexplicably develops confusion, disorientation, seizures or other neurological signs that progress rapidly
over a matter of weeks. A spinal tap with analysis of cerebrospinal fliud helps confirm the diagnosis. A CAT scan or MRI is
useful in determining the form and location of the disease.
Brain Tumors and Abscesses Brain tumors are not common. They tend to occur
in middle-aged and older dogs. The highest incident is found in the short-nosed breeds that have large domed heads, including
the Boxer, Bulldog and the Boston Terrier. Tumors that can metastasize to the brain include cancers of the mammary glands,
prostate and lungs as well as hemangiosarcoma. Symptoms depend on the tumor's location and rate of growth. Tumors in the
cerebrum produce seizures and/or behavioral changes. The dog may exhibit a staggering gait, head tilt, nystagmus (rhythmic movement of the eyeballs) and limb weakness or paralysis. These signs
are progressive and continue to worsen. The late signs are stupor and coma. A brain abscess is a collection of pus in or around
the brain. The signs are similar to those of a brain tumor. These dogs will often have a fever. There may be a prior infection
in the oral cavity, inner ear or respiratory tract.
Strokes Strokes are not common in dogs. A stroke can be caused by bleeding into the brain, obstruction
of an artery caused by an embolus or clotting of a cerebral artery. An embolus is a clot that develops at another site and
travels through the vascular system to a smaller vessel, where it becomes lodged and interupts blood flow to the area served
by that artery. This results in death of tissue in the infected area, a condition called infarction. Most strokes in dogs
are caused by emboli. Bleeding in the brain is seen with ruptured cerebral blood vessels and brain tumors. Spontaneous bleeding
may occur with coagulation disorders. Disseminated intravascular coagulation is a cause of both bleeding and infarction. Some
hemorrhagic strokes occur for unknown reasons. Infarctions can occur with Rocky Mountian spotted fever, hardening of the arteries
associated with hypothyroidism and for unknown reasons. The onset of stroke is sudden. The signs depend on the location and
extent of the bleeding or brain infarction. They include behavioral changes, disorientaion, seizures, weakness or paralysis
on one side of the body, stupor and coma. Large strokes are usually accompanied by cardiac ahrrythmias and collapse. The diagnostic
work is similar to that for a brain tumor.
Hereditary
Diseases Hereditary nervous system disease are not common. Most run in families. Affected individuals should not be bred. Hereditary Myopathies (muscular dystrophy) Muscular dystrophy is actually a group of genetically determined
diseases in which there is a progressive degeneration of skeletal muscle (the muscles that are attached to the skeleton). Nerves and muscles work hand in hand, so damaged nerves will lead to
damaged muscles. Weakness is the predominant sign. The diagnosis can be suspected by finding high serum CPK levels. Many of
these problems will require a muscle biopsy for an accurate diagnosis.
Hereditary Myopathy of Labrador
Retrievers This disease is inherited as an autosomal recessive trait. Signs of weakness begin at 6 weeks to 7 months of
age. There is a marked decrease in exercise tolerance. An affected pup may have difficulty holding up her head, bunny hop
when running and collapse after a brief exertion. The disease may affect the muscles involved in chewing and swallowing, resulting
in drooling and the development of megaesophagus. Exposure to cold greatly exacerbates the symptoms. Sex-Linked Muscular Dystrophy This disease affects Golden Retrievers, Irish Terriers, Samoyeds,
Rottweilers, Belgian Tervurens and Miniature Schnauzers. It is transmitted on the X-chromosome from the dam. Affected pups
are weak at birth and often die. Those who survive develop a stilted gait, drooling, muscle waisting and stunted growth. The
condition may stabilize temporarily at 6 months of age, but later progresses.
Bouvier des Flandres Myopathy This disease
affect only the muscles of swallowing, resulting in regurgitation and megaesophagus. Signs appear at about 2 years of age.
With severe megaesophagus the outlook is guarded. Distal Myopathy
of Rottweilers This disease affects the legs and feet, producing an abnormal stance with splayed toes and weak hocks.
(There is no treatment for this disease). Myotonia This disease affects Chow Chows, Staffordshire Terriers, Rhodesian Ridgebacks, Cavalier
King Charles Spaniels, Great Danes , Golden Retrievers and Irish Setters. Signs appear when the pups begin to walk. They include
stiffness upon rising and walking. This is followed by a progressive stiffening of the gait as the dog exercises.
Degenerative Myelopathy This is a degenerative
disease of the spinal cord that appears to run in families. It occurs primarily in German Shepherd Dogs but has been diagnosed
in many breeds. It is the most common cause of hindquarter weakness in German Shepherds and their crosses. The Siberian Husky,
Old English Sheepdog, Rhodesian Ridgeback, Weimaraner and other large breeds are also affected. Among smaller dogs, older
Pembroke Welsh Corgis are seen with this problem. This disease manifests itself as a slowly progressive weakness or paralysis
of the hind limbs, along with an unsteady gait suggestive of hip dysplasia. The toenails on the hind feet may show abnormal
wear from dragging on the ground. This appears to be autoimmune in nature and similar to multiple sclerosis in people.
Inherited Neuropathies There are a
number of rare diseases in which sensory and motor nerves degenerate. With loss of sensation and motor function, an affected
dog does not feel the position of his limbs, is unable to position them correctly to prevent stumbling and fails to withdraw
a leg from a painful stimulus. The diagnosis is made by sensory and motor nerve conduction studies. There is no cure; but
because of the slow progression of the disease, some dogs live comfortably for many years. Most of these neuropathies are
inherited as autosomal recessive traits. Some of the most common ones are noted here. Neuropathy of German
Shorthaired and English Pointers is first noted at 3 to 4 months of age. The pup with this sensory neuropathy begins to lick and bite at his paws,
which become swollen, reddened, ulcerated and eventually mutilated. Loss of sensation can extend up the limb and involve the
trunk. The mode of inheritance is autosomal recessive. Dachshund sensory neuropathy begins in long-haired Dachshunds at 2 to 3 months of age. It is characterized
by uncoordinated gait, urinary incontinence and loss of sensation over the entire body. Self mutilation of the penis may be
the first sign in males. Global cell leukodystrophy is caused by an enzyme deficiency that results in degeneration of nerve cells. It occurs in West
Highland White Terriers, Cairn Terriers, Beagles, Pomeranians and Poodles. Signs are unsteady gait, head tremors, nystagmus
(a rhythmic movement of the eyeballs) and blindness. Scotty cramp is an autosomal recessive disease in Scottish
Terriers where puppies show increased muscle tone when excited, stressed or exercising vigorously. They show a stiff, hyper
gait. Hypertrophic neuropathy in Tibetan Mastiffs begins at 7 to 12 weeks of age and is characterized by hind-limb weakness that
progresses to generalized weakness and ultimately, an inability to stand. Some dogs maintain a degree of strength. This is
a autosomal recessive disease. Polyneuropathy in Alaskan Malmutes show up about 12 to 18 months of age. Initially, dogs show exercise intolerance
but this can progress to paralysis. Some dogs may stabilize, but most dogs continue on a downward trend. Treatments have not
been effective. Hypomyelination diseases manifest when myelin, which forms a sheath around nerve fibers, is not completely developed at birth.
The result is that nerve impulses are conducted very slowly. Hypomyelination occurs in Chow Chows, Weimaraners, Samoyeds and
Bernese Mountain Dogs. One form called the shaking puppy syndrome, is a recessive trait that affects only males. The characteristic
sign of hypomyelination is muscle tremors involving the limbs, trunk, head and eyes of newborn puppies. The tremors get worse
with activity and disappear with sleep. Severely affected puppies show uncoordinated body movements and are unable to stand.
(There is no cure for the disease). Tremors in Chow Chows and Weimaraners may
improve gradually and disappear by one year of age.
White Dog Shaker Syndrome This syndrome
occurs primarily in adult dogs with white coats, although dogs with other coat colors are occasionally affected. The disease
occurs most often in small breeds, including West Highland White Terriers, Maltese, Bichon Frises and Toy and Miniature Poodles.
It is characterized by the sudden appearance of tremors, sometimes accompanied by wild and random movement of the eyes. The
disease affects the cerebellum, which coordinates muscle movement. Sudden trembling that involves the entire body and head
is the main sign. The dog does not shake while sleeping, but the more he moves, the worse the tremor gets. These tremors can
be disabling. The cause is unknown, but an autoimmune basis has been suggested.
Cerebellar Diseases Cerebellar degeneration is a slowly progressive disease in which the nerve cells in the cerebellum die.
The disease has been described in numerous breeds, including the Kerry Blue Terrier, Gordon Setter, roughed-coated Collie,
Great Dane, Labrador Retriever, Golden Retriever, Cocker Spaniel, Airedale Terrier, Samoyed, Cairn Terrier and Bullmastiff.
Affected puppies appear normal for the first two months of life, but then begin to show uncoordinated body movements such
as jerking, stumbling, falling and over reaching with the paws. Although there is no cure, cerebellar degeneration stabilizes
in some puppies, allowing them to remain active. Cerebellar hypoplasia is a condition in which the cerebellum is abnormally small at birth. A hereditary form has been reported in Airedales,
Gordon Setters and Chow Chows. A nonhereditary form has been described in Bull Terriers, Weimaraners, Dachshunds and Labrador
Retrievers. Signs are similar to those of cerebellar degeneration, but are observed shortly after birth when puppies first
begin to crawl. Some puppies compensate and make good pets. Lissencephaly is a condition seen rarely in Lhasa Apsos, Irish Setters, Wire Fox Terriers and Samoyeds. The brain
is smooth without the gyri or folds normally seen. Affected dogs may show behavioral abnormalities, including difficulty
house training and sometimes seizures.
Hydrocephalus Hydrocephalus
is caused by the extensive accumulation of cerebrospinal fluid in the ventricles of the brain. The enlarged ventricles damage
the cerebral cortex by compressing it against the skull. Most cases are congenital. Some are acquired through trauma, brain
infections or tumors. Breeds with an increased risk of congenital hydrocephalus include the Maltese, Yorkshire Terrier, Chihuahua,
Lhasa Apsos, Pomeranian, Toy Poodle, Cairn Terrier, Boston Terrier, Pug, Pekinese and Bulldog. Hydrocephalus causes seizures,
Partial or complete blindness and dementia. The diagnosis is made by skull X-rays, ultrasound of the ventricles and, in difficult
cases, by CT scan or MRI. A characteristic enlargement of the dome of the skull occurs in congenital hydrocephalus, but this
may not be seen until the puppy is several months old. An increase in ventricular size without clinical signs has also been
noted. This is called subclinical hydrocephalus. In certain lines of toy breeds with a high incidence of clinical and subclinical
hydrocephalus, EEG screening and breeding only dogs with normal EEGs has reduced the incidence of hydrocephalus.
Seizure Disorders A seizure is
caused by an abnormal burst of electrical activity within the brain, commonly in one of the cerebral hemispheres. The electrical
activity sometimes spreads out and involves other areas, including the mid-brain. A typical grand mal seizure is preceded
by a period of altered behavior, called the aura. During the aura dogs may be restless and anxious, cry out, demand affection
or seek seclusion. The actual seizure normally lasts less than two minutes and is characterized by collapse with rigid extension
of the legs. The dog becomes unconscious and may stop breathing for 10 to 30 seconds. This is followed by rhythmic jerking
of the legs (which resembles
running or paddling). Some dogs
also chomp, chew, drool or urinate and defecate. As the dog regains consciousness there is a postseizure state characterized
by disorientation and confusion. The dog may stumble into walls and appear blind. The postseizure state can persist for minutes
or hours. Grand mal seizures are typical of epilepsy. A focal motor or partial seizure is one in which the jerking or twitching
is limited (at least initailly) to a particular part of the body. A focal
seizure usually indicates a specific brain legion, such as a scar, tumor or abscess. Seizures are commonly associated with
brain injury, encephalitis, heat stroke, brain abscess, brain tumor, stroke, poisoning, kidney failure or liver failure. Seizures
associated with a concussion frequently occur weeks or months after the head injury and are caused by a focus of scar tissue
in the brain. Postencephalitic seizures occur three to four weeks after the onset of encephalitis. Distemper, in particular,
is characterized by attacks that begin with chomping, tongue chewing, foaming at the mouth, head shaking and blinking, all
followed by a dazed look. Postvaccination seizures have been described in puppies under 6 weeks of age following inoculation
with with a combined distemper-parovirus vaccine. A bitch may develop low blood calcium levels after whelping and have seizures.
A sudden drop in blood sugar (hypoglycemia) can also trigger a seizure. This occurs in
newborn pups with cardiopulmonary syndrome. It can also occur in small breed puppies who have not been fed adequately. A common
cause of hypoglycemia is giving too much insulin to a diabetic dog. Common poisons that cause seizures are animal baits such
as strychnine, antifreeze (ethylene
glycol), lead, insecticides (organophosphates), and chocolate. Seizures caused by organophosphates are preceded
by drooling and muscle twitching. Exposure to a spray, dip or premise treatment suggests the diagnosis. There are a number
of conditions that while not true seizures, are often mistaken for them. Bee stings for example: can cause frenzied barking
followed by fainting or collapse. Cardiac ahrrythmias can be mistaken for seizures because they cause loss of consciousness
and collapse.
Epilepsy Epilepsy is a recurrent
seizure disorder that may be idiopathic or acquired. Acquired epilepsy has identifiable cause, such as a mass of scar tissue
in the brain following a head injury. Idiopathic epilepsy occurs in up to three percent of dogs and accounts for 80 percent
of recurrent seizures. The cause is unknown, although an imbalance in chemicals that transmit electrical impulses in the brain
has been suggested. Seizures, usually of the mal grand type, begin between six months and five years of age. Breeds in which
the condition is inherited include Beagles, Dachshunds, Keeshonden German Shepherd Dogs, Belgian Tervurens and others. Breeds
with a high incidence, but in which inheritance has not yet been established, include Cocker Spaniels, Collies, Golden Retrievers,
Irish Setters, Poodles, Miniature Schnauzers, Saint Bernards, Siberian Huskies and Wire Fox Terriers. Even mixed breeds can
be afflicted with epilepsy. If the diagnosis is truly epilepsy, the attacks must be recurrent and similar. Epileptic seizures
usually become more frequent with time. A typical epileptic seizure has three phases: an aura, a generalized grand mal seizure
and a postseizure state as described in the previous section. All three phases may not be seen, because many seizures occur
while the dog is resting or asleep. Furthermore, in some cases the seizure is atypical. Instead of a classic grand mal convulsion,
the dog exhibits strange behavior such as frenzied barking, licking or chewing at himself, staring into space or snapping
at invisible objects. This is called a psychomotor seizure and is believed to arise from a center lower in the brain (not the cerebrum). Focal motor seizures, as already discussed, indicate a lesion
in the brain. An abnormal neurological exam or EEG during a period where there have been no recent seizures also indicates
a legion in the brain. These findings eliminate the diagnosis of epilepsy. Further the diagnostic tests include a spinal tap
with cerebrospinal fluid analysis, skull X-rays and a CT scan or MRI.
Narcolepsy and Cataplexy Narcolepsy and
cataplexy are uncommon disorders of the sleep mechanism in which a dog is excessively sleepy all day (narcolepsy) or experiences sudden muscle paralysis and collapse (cataplexy). Between attacks the dog is completely normal. Narcolepsy can occur without cataplexy
and vice versa, although narcolepsy alone is difficult to recognize in dogs. A dog may have one or many episodes of
collapse in a day, each lasting a few seconds or up to 30 minutes. The attacks can usually be reversed by petting the dog
or making a loud noise. Compulsive Behavior There are some unusual behaviors in dogs that may, in fact be partial seizures. These
include fly biting and tail chasing/spinning. In the fly biting situation, the dog may be sitting quietly and suddenly starts
to bite at imaginary flies. These dogs can usually be distracted and never lose consciousness. Cavalier King Spaniels are
one breed in which this behavior is seen. In the tail biting/spinning sequence, the dog is intent on trying to catch
her tail and spins rapidly. These dogs may become so intent that it is difficult to break their concentration. Bull Terriers
and German Shepherd Dogs may have an inherited component to this behavior. Aggressive Behaviors Some syndromes
in dogs, such as rage syndrome and sudden-onset aggression, may have a physiological basis such as seizures or a metabolic
disturbance in serotonin levels. These dogs may suddenly switch from acting normally to viciously attacking whomever or whatever
is nearest. Minutes later, the dogs often act as if nothing happened. English Springer Spaniels and Cocker Spaniels
may have an inherited predisposition to these problems. Aggressive behavior has also been associated with hypothyroidism in
Golden Retrievers, German Shepherd Dogs and Shetland Sheepdogs. Thyroid levels should be checked in any dog with newly appearing
aggressive behavior.
Coma Coma is a depressed level
of consciousness. It begins with confusion, progresses through stupor, and ends up with complete loss of consciousness. A
dog in a coma is insensitive to pain and cannot be awakened. Coma occurs with oxygen deprivation, brain swelling, brain tumor,
encephalitis and poisoning. Many diseases that cause seizures progress to coma. Following a head injury with cerebral concussion,
coma can occur without progressing through the earlier stages. Low blood sugar (hypoglycemia) is a common cause of coma. It tends to occur in toy breed puppies and adult hunting dogs after
a long day in the field. A common iatrogenic cause is giving to much insulin to a diabetic dog. Another cause of coma is prolonged
hypothermia. Coma related to high fever and heat stroke is a serious complication that leads to permanent brain damage and
is usually preceded by seizures. Vigorous efforts must be made to bring down the fever. Coma is also especially ominous when
it is associated with brain trauma or when it occurs in the late stages of kidney or liver disease. Common poisons that may
cause coma are ethylene glycol (antifreeze), barbituates, kerosene, turpentine, arsenic, cyanide, organophosphates, plants, chocolate and lead. A dog found in a coma in a closed car or in
an airtight space may have smothered or developed carbon monoxide poisoning.
Weakness or Paralysis There are several
diseases - none of them very common - that attack the motor nerves, causing weakness and paralysis but leaving the sensory
nerves intact. These diseases resemble one another and are difficult to tell apart. Tick Paralysis The saliva of a variety of ticks contains a toxin that affects the motor nerves, producing
weakness and paralysis. Signs appear about one week after the dog has been bitten by the tick. Over the next 48 to 72 hours,
the dog grows progressively weaker. Sensastion to a pin prick is normal. In time the paralysis reaches a level where the dog
collpases and is unable to to lift her head. Death can occur from respiratory arrest.
Botulism Botulism is a paralytic
disease cause by neurotoxins produced by the bacteria Clostridium botulinum. The disease is acquired by eating infected carcusses or improperly canned vegetables and meats.
Coonhound Paralysis The cause of the disease is unknown. It is believed to be an immune-mediated disease with antibodies directed at the dog's peripheral nerves. The agent
triggering the immune reaction may be a virus or a bacteria. It occurs most often in hunting dogs one to two weeks after having
had contact with a racoon. The illness is not limited to Coonhounds. Paralysis begins as weakness in the hindquaters and progresses
forward until the dog is unable to stand. During this time the dog remains anxious but alert. The paralysis can affect the
muscles involved in respiration and swallowing. It reaches its peak at about 10 days. Muscle atrophy may be dramatic.
Myasthenia Gravis This is a rare
disease caused by a deficiency of acetylcholine receptors, normally present at the junction of nerve endings and muscle cells.
When an animal decides to move a muscle, the nerve endings release acetylcholine, which is a neurotransmitter. The acetylcholine
carries the nerve impulse across the junction, where acetylcholine receptors respond and send the nerve impulse on its way. A
reduction in the number or function of these receptors produces generalized muscle weakness, made worse by exercise. Weakness
is most apparent in the hindquarters. Dogs with myasthenia gravis have difficulty getting up and exhibit a swaying or staggering
gait. There is a focal form of myasthenia gravis that affects only the muscles involved in swallowing. The dog is unable to
swallow solid food and develops enlarged, dilated megaesophagus. Aspiration pneumonia often follows. A congenital form of
myasthenia gravis is inherited as an autosomal recessive trait. It occurs in Jack Russell Terriers, Springer Spaniels and
Smooth Fox Terriers. An acquired form of myasthenia gravis occurs in all breeds, but is seen most often in Golden Retrievers,
German Shepherd Dogs, Labrador Retrievers, Dachshunds and Scottish Terriers, often occuring at 1 to 4 years of age or 9 to
13 years of age. Acquired myasthenia gravis is an immune-mediated disease
in which auto-antibodies are directed at and destroy the acetylcholine
receptors. Hypothyroidism can occur at the same time as autoimmune myasthenia gravis. Occasionally myasthenia gravis is related
to the tumor of the thymus gland, but this is rare. The diagnosis of myasthenia gravis is based on neurological examination.
A serologic test for diagnosing autoimmune myasthenia gravis is available.
Hypokalemia (Low Serum Potassium) Hypokalemia, a condition
in which the dog has low serum potassium, is a metabolic cause of generalized muscle weakness. Loss of potassium occurs with
severe vomiting. It also occurs with the long-term use of diuretics
that cause the kidneys to excrete potassium, such as lasix (
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