Nervous System Disorder


Cerebellar Hypoplasia

Cerebellar hypoplasia is a defect in the brain (cerebellum) that results in a loss of fine-motor coordination. In cats, it is caused by infection with feline distemper virus while the kittens are still in the mother’s uterus or shortly after birth. Affected pets have trouble walking and maintaining their balance. Diagnosis is afforded via physical exam, neurologic exam, special imaging studies and/or necropsy (examination of the dead). There is no treatment. Preventing the spread of feline distemper virus is accomplished through vaccination.

Cognitive Dysfunction Syndrome (CDS)

As a result of advancements in veterinary medicine and surgery, dogs are living longer. An estimated 13 million dogs in the United States alone are 8 years old or older. Dogs in their later years undergo a variety of physical and metabolic changes that may result, in among other things, behavioral and cognitive changes. Cognitive function in dogs includes spatial orientation, housetraining, recognition and interaction. Cognitive Dysfunction Syndrome is the age-related deterioration of cognitive abilities that cannot be attributed to such medical disorders such as neoplasia, infection or organ failure. CDS is offend referred to as “old dog syndrome” or “senility”. The disorder is characterized by one or more of the following: disorientation/confusion; changed responsiveness to family members; changes in the sleep-wake cycle; inactivity; relapse in housetraining. Cognitive Dysfunction Syndrome is a common, recognizable disorder in older dogs. Owners need to present pets to their veterinarians at the early signs of behavioral changes in order to evaluate the difference between “normal age changes” and CDS. Diagnosis is afforded via accurate history, physical exam, complete blood count, blood chemistries, other disorder eliminating testing and response to treatment. Treatment includes administration of the drug selegiline hydrochloride.


A blow to the head can cause bleeding and/or swelling of the brain. There is little room for swelling or bleeding within the skull and damaged brain tissue can become compressed or squeezed, impairing brain function. Severe swelling or bleeding may even produce permanent brain damage. A concussion is characterized by brief loss of consciousness, followed by temporary weakness, disorientation, dizziness, nausea and vomiting. A contusion is actual bruising of the brain resulting in some brain damage. Diagnosis of either is via history, physical exam, imaging studies and neurological tests. Treatment may include rest, anti-inflammatories and DMSO (dimethysulfoxide).

Degenerative Myelopathy

Degenerative myelopathy is a slowly progressing paralysis of the hind quarters in middle-aged to old German Shepherds. The underlying disease is degeneration of the white matter of the spinal cord. Signs include weakness, ataxia, paralysis and wasting of the rear legs. The forelegs function normally, and otherwise the affected dogs are in good health. Diagnosis is afforded via physical exam, neurologic exam, imaging studies and electrodiagnostic tests. Treatment may include glucocorticoids and supportive care.


Encephalitis is inflammation of the brain. This disorder is usually related to some other disease. Causes include canine distemper virus, other viruses, bacteria, neoplasia, head trauma and chemical toxins. Signs of encephalitis may include mental dullness, walking in circles, ataxia, blindness and seizures. Dogs with canine distemper encephalitis often exhibit “chewing gum” motions of the jaws. Diagnosis is afforded via physical exam, complete blood count, blood chemistries, cerebral spinal fluid (CSF) analysis, cytology, culture and sensitivity. Treatment may include antimicrobials, antinflammatories, glucocorticoids and supportive care. Unfortunately the prognosis (outlook) is usually poor.


Epilepsy is a condition of recurring sudden, excessive discharge of electrical energy in groups of brain cells producing a seizure or convulsion. Epilepsy affects approximately 2-3% of dogs and 0.5% of cats. Signs range from short periods of mental lapse to full blown seizure activity. Diagnosis is afforded via physical exam, complete blood count, blood chemistries and imaging studies. Epilepsy usually becomes apparent between 6 months and 7 years of age affecting any breed. Treatment may include phenobarbital, potassium bromide, gabapentin or correction of underlying disorders. Treatment does not cure the disease but instead should decrease the frequency, duration and severity of seizures.

Horner's Syndrome

Horner’s syndrome is a group of signs that indicate an abnormality along a particular nerve pathway called the sympathetic trunk. The sympathetic trunk is part of the autonomic nervous system which controls involuntary responses that aid the body in emergencies and maintain the normal internal state of the body. Degeneration, neoplasia, infections, diseases and trauma along any portion of the sympathetic pathways may present certain recognizable signs referred to as syndromes. One such syndrome, Horner’s syndrome, includes drooping of the upper eyelid, a small pupil, elevation of the third eyelid and slight retraction of the eyeball within the socket.


Hydrocephalus (“water on the brain”) occurs when excessive fluids accumulates within the brain producing increased pressure. Causes may include congenital defects (present at birth), meningitis, neoplasia and head trauma. The disease is most common in small breeds with dome-shaped heads, such as Chihuahuas. Signs of hydrocephalus may include an enlarged head, prominent forehead, lack of coordination, impaired vision, mental dullness, seizures and misdirected eyes. Animals with mild cases may not exhibit these signs and only appear abnormal in times of stress, excitement or head trauma. Diagnosis is afforded via skull radiography, special imaging studies (eg. magnetic resonance imaging (MRI), computer assisted tomography (CT) scan), cerebral spinal fluid analysis and blood chemistries. Treatment may include medication and careful supervision to prevent stress and head injury in mild cases. Severe cases are treated surgically.


Hypoglycemia is low blood sugar. In this disorder, the body is temporarily unable to use stored reserves of sugar to meet increased energy demands. These increased needs may result from lack of nutrition, infection, emotional stress, excitement or vigorous exercise. Signs of hypoglycemia may include dizziness, fainting and convulsions. Diagnosis is based on history and blood sugar assays. Treatment may include oral or intravenous sugar replacement.


Polyradiculoneuritis is a nerve disorder characterized by weakness that begins in the hindquarters and rapidly moves forward (1-2 days), eventually involving the entire body. Signs also may include increased sensitivity to pain, change in bark and trouble swallowing. The disorder affects adult dogs of any age, breed, or sex, and is frequently seen in hunting dogs 7-14 days after contact with a racoon. Diagnosis is afforded via history, physical exam and electromyography (EMG). Treatment is supportive care (eg. physical therapy, bladder evacuation, etc.). Most dogs with coonhound paralysis fully recover within weeks or months. Complications of the disease may include bladder infections, aspiration pneumonia, tendon contraction and decubital ulcers. Recovered dogs do not gain immunity and may become affected again.


Useful Information Regarding Seizures

  • Seizures are non-painful.
  • Seizures rarely impair a pet’s “thinking ability.”
  • Seizures rarely change a pet’s responses to owner.
  • There is a minimal chance of death during a seizure.
  • A normal life span is expected for most idiopathic canine epileptics.
  • The major therapeutic objectives include:
  • Reduce the frequency, severity and number of seizures per cluster.
  • Avoid status epilepticus (continuous grand mal seizure).
  • To attain a seizure frequency tolerable to owner.
  • Idiopathic epilepsy cannot be cured, only controlled.
  • Anticonvulsant side effects include changes in appetite, water consumption, activity and liver function. Re-evaluations at 6 month intervals are recommended.
  • Accurate, descriptive records of seizure frequency and character will provide information for drug dose adjustment.
  • Seek veterinary care if seizure activity lasts longer than 10 minutes.
  • Oral medications take several days to have effect when treatment has begun. Seizures are common during this initial period.
  • Medications must be given consistently on schedule or seizure activity may result.
  • The longer an animal has had a seizure disorder, the better the prognosis.
  • If a dog has had no convulsions for 1 year, your veterinarian may slowly decrease the dose of medication over months. Only a few dogs may be eventually weaned off medication.
  • Avoid the use of phenothiazine derivative drugs as they may precipitate seizures in epileptics. Most of the antihistamine tranquilizers and motion sickness drugs are phenothiazine derivatives.
  • In some dogs, hormones can precipitate seizures. Estrogen levels are elevated during heat in bitches and some seizures may be observed at this time. Ovariohysterectomy is a logical corrective measure.
  • Epileptics should not be used for breeding.

Medication for seizures is not given to cure but rather to control the disease. Success of therapy is measured by the ability to decrease the frequency, duration and severity of individual seizures.


Tetanus is a disease caused by spore forming bacteria (Clostridium tetani) that produce toxins which are very damaging to the nervous system. The spores are very resistant to conditions that could destroy most other types of bacteria. They are found throughout nature in soil and in human and animal waste. Tetanus organisms usually enter the body through deep puncture wounds, causing signs of disease 4-20 days after entering the body. Signs of tetanus may include stiffness of limbs, difficult breathing and contraction of facial muscles (“sardonic expression”). Death can occur due to paralysis of the breathing muscles. Diagnosis is afforded via accurate history, physical exam, serology and electrodiagnostics. Treatment may include antibiotics, antitoxin and supportive care.

Vestibular Disease

Vestibular disease is a disturbance of the pet’s vestibular or balancing and orientation system. Causes include metabolic disorders, middle ear infections, neoplasia, other infections, trauma and unknown (idiopathic) causes. Signs include tilted head, uncontrolled eye movement (nystagmus), disorientation, nausea and ataxia. In cats the disease occurs most frequently during the late summer and fall with sudden onset. The cause is unknown, but most cats recover within 2 – 6 weeks. Diagnosis of vestibular disease is afforded via history, physical exam, complete blood count, blood chemistries and imaging studies. Treatment is directed at underlying disorders and may include glucocorticoids and supportive care.