Diane, Penny and Tarzan (via yellowpages.com)

A high-field MRI of the entire thoracolumbar spine showed a contrast-enhancing mass in the mid-thoracic spine.  Surgery was performed at Southeast Veterinary Neurology and a large mass was removed surrounding the spinal cord.  Here is a video of Frankie a few months after surgery.  Note that his hair coat is still growing after surgery.  He is much more comfortable and is walking better.  It has been over 18 months since Frankie’s surgery and he remains normal.

The following day, Nico re-presented to his regular veterinarian, however, at this point he was unable to stand and walk.  He was referred to Southeast Veterinary Neurology.  On examination, Nico was laterally recumbent.  He did not respond to stimuli.  He had ventral strabismus.  The remainder of cranial nerves were normal.  When supported, he was flaccid in all four legs.

Note that this episode looks similar to a seizure–he seems unconscious, vocalizes, has involuntary facial twitches, and paddles.  However, note that the episode can be stopped by distracting him. I was suspicious of a particular disease, but wanted to see what his response to food would be.

Nico has narcolepsy/cataplexy. Narcolepsy is a syndrome characterized by abnormalities in the sleep-wake cycle.  Excessive sleepiness is manifested as drowsiness and “sleep attacks”.  Cataplexy is a brief episode of flaccid paralysis usually brought on by excitement.

There are two forms of narcolepsy in dogs.  A genetic basis has been found in Labrador Retrievers and Doberman Pinschers and is due to a mutation involving the hypocretin receptor 2.  Sporadic cases can happen in any breed and is caused by a loss of hypocretin 1-producing neurons in the hypothalamus.

Diagnosis in dogs is based on finding appropriate clinical signs (collapse or even falling asleep due to excitement).  The source is often food but may include other sources of excitement.  It is important to differentiate narcolepsy/cataplexy from other diseases that may cause collapse such as seizures, syncope, myasthenia gravis, myotonia or other diseases.

Treatment involves medications.  Nico was treated with imipramine, a tricyclic antidepressant that acts via blocking cellular norepinephrine and serotonin reuptake in the CNS.

Here is a video of Nico after treatment on the day of discharge.

The other important part of the history is that she would ‘spit up’ food shortly after eating.  After further questioning, the ‘vomiting’ was more consistent with regurgitation.

Radiographs of her chest showed megaesophagus.  Normally the esophagus is not visualized on plain radiographs.  When the esophagus is filled with air, the esophageal walls are visible on radiographs.

Arrows outline the esophagus which is usually not visible on plain radiographs

Exercise-induced weakness combined with regurgitation is suggestive of a problem in the lower motor neuron, and myasthenia gravis is considered the most likely differential.

The tests that are indicated in cases of suspected myasthenia gravis include a CBC, chemistry panel, thyroid panel, thoracic radiographs, a tensilon (edrophonium) test, and an acetylcholine receptor antibody.  A tensilon test was performed.  A positive response is strongly suggestive of myasthenia gravis, however an acetylcholine receptor antibody titer is considered the ‘gold standard’.  See the following video to see her after her tensilon test.

The acetylcholine receptor antibody was positive, which is diagnostic of myasthenia gravis.  Pyridostigmine, a long-acting anticholinesterase medication was prescribed.  Prognosis is guarded in that many dogs get aspiration pneumonia secondary to chronic regurgitation.

If you would like to learn more about myasthenia gravis, please feel free to contact Dr. Wong at (305) 274-2777 or via email at DrWong@SEVNeurology.com

Back Pain, Weakness and Paralysis in Dogs

Intervertebral disk disease is a common spinal cord disease in dogs that can cause back pain, difficulty walking, or inability to feel the back legs (paralysis).  Certain breeds including the dachshund, shih tzu, Pekingese and Beagle are commonly affected.  Intervertebral disk can affect any part of the canine spine, however, this article will focus on the thoracolumbar (‘mid-back’) spine.

The canine vertebral column (spine) is made up of individual vertebrae (bones).  There are seven cervical (neck) vertebrae, thirteen thoracic vertebrae (these have ribs), seven lumbar vertebrae (low back), three fused sacral vertebrae, and a variable number of caudal (tail) vertebrae.  Most vertebrae are made up of a ‘body’ at the base, a pedicle and arch (side and top) and a dorsal spinous process.  The vertebral canal is the ‘tunnel’ formed by the vertebrae that the spinal cord travels through and is protected by.  Between most of the vertebral bodies (there are exceptions) is an intervertebral disk.  The intervertebral disk is made up of the outer annulus fibrosus and the inner gelatinous nucleus pulposus.  A ‘jelly doughnut’ analogy is often used in describing the intervertebral disk, in which the annulus fibrosus is the outer doughnut, while the nucleus pulposus is the inner jelly portion.  The intervertebral disk acts as a ‘cushion’ between each vertebral body.

In some breeds, the inner nucleus pulposus loses it’s ‘jelly-like’ properties and becomes dry and brittle.  The dorsal (top) of the annulus fibrosus is thinner than the rest of the annulus fibrosus.  In dogs that herniate (or ‘slip’) a disk, the nucleus pulposus extrudes dorsally from the annulus fibrosus and may forcibly strike the spinal cord and/or compress the spinal cord.  This leads to signs of intervertebral disk disease.  Signs of thoracolumbar intervertebral disk disease  include back pain, pelvic limb ataxia (walking wobbly), inability to stand, inability to move the rear legs, or even inability to feel the back legs.  A grading scale is used in dogs:

1. Grade 1) Pain only–these dogs are able to walk normally, but exhibit signs of pain including reluctance to move, reluctance to jump, shivering, crying, muscle spasms, and/or a tense abdomen.
2. Grade 2) Ambulatory paraparesis–these dogs are able to walk, but are weak and wobbly in the rear legs.  They may cross their back legs when walking, splay out, knuckle over or stumble in their back legs.
3. Grade 3) Non-ambulatory paraparesis–these dogs are still able to move their legs and wag their tails, but are not strong enough to support their own weight and walk.
4. Grade 4)  Paraplegia–these dogs have no voluntary movement in the rear legs.
5. Grade 5) Paraplegia with absent nociception (no ‘deep pain’)–in addition to being unable to move the back legs, they are unable to feel their back legs.

There are other diseases that can cause similar clinical signs of spinal cord disease including meningitis/myelitis, spinal tumors, trauma, infection, malformations, vascular problems and others.  A thorough neurological examination can give the veterinarian an idea of which of these are more likely than others, but tests are necessary to accurately determine the cause.  Spinal radiographs are useful for screening for disk infection and bony tumors, but typically are insufficient to diagnose intervertebral disk disease.  Myelography is a technique that involves injecting contrast around the spinal cord to visualize it on radiographs.  A CT scan is useful (often combined with a myelogram) and allows the body to be visualized in ‘slices’.  Magnetic resonance imaging (MRI) is considered the imaging modality of choice when visualizing the soft tissues of the body, including the nervous system.  High-field MRI offers several advantages over low-field MRI, CT and/or myelography.

MRI of the thoracolumbar spine showing a herniated intervertebral disk (arrow)

Treatment depends on the severity of the signs, but can be divided into surgical and non-surgical options.  For dogs with a first episode of back pain or mild pelvic limb ataxia, a conservative approach of cage rest and medications may be elected.  Dogs with more severe signs (grade 2-5) or recurrent or persistent back pain that does not respond to rest and medications are best managed with surgery to decompress the spinal cord.  After examination and MRI, the size, site and side of the disk herniation can be located.  A hemilaminectomy (removal of one side of the side of the vertebrae) can be performed to allow the neurosurgeon to remove the herniated disk material and decompress the spinal cord.

For dogs that are category 1-4, the chances of success are about 95% in the hands of an experienced neurosurgeon.  For dogs in categories 1-4 that are managed non-surgically, the chances of regaining the ability to walk are about 50-60%.  However, dogs that are category 1-4 that are managed without surgery have a much higher risk for recurrence, may take longer to improve, and are at risk for worsening when compared to those that are treated with surgery.
Dogs that are category 5 (paraplegic with no ‘deep pain’ perception) are a surgical emergency.  The chances of recovery are significantly lower than those that can still feel their back legs.  If surgery is to be successful, it should be performed as soon as reasonably possible and certainly within 48 hours of losing the ability to feel the back legs.  Dogs that are paraplegic with absent nociception are at risk for myelomalacia, an extremely serious condition that is typically progressive and fatal.

Intervertebral disk disease is a common spinal cord disease in dogs that can cause pain, difficulty walking, or inability to feel the back legs.  Diagnosis is based on examination and advanced imaging such as high-field MRI.  Prognosis depends on the severity of signs and therapy chosen.  Surgery often offers the best chances for long-term success.

Head Tilt and Balance Problems in Dogs and Cats

Balance problems in dogs are a relatively common neurological condition.  Head tilt, incoordination and abnormal eye movements are common clinical signs.  Owners may state that their dog has vertigo, is off balance, or had a stroke.

The vestibular system can be thought of as the peripheral vestibular system and the central vestibular system.  The peripheral vestibular system is made up of the parts of the vestibular system that are outside of the brain (receptor in the inner ear and the nerve).  The central vestibular system is the part of the balance system inside the brain (vestibular nuclei and their connections to other parts of the brain and spinal cord).

Clinical signs of dysfunction of the vestibular system include head tilt (the head is cocked to one side so that one ear is closer to the ground than the other), vestibular-quality ataxia (leaning/falling/rolling to the side), and abnormal eye movements or position (nystagmus or strabismus, respectively).  A thorough neurological examination is used to determine if the problem is affecting the peripheral or central vestibular system.  This is important to determine since the diseases, treatments and prognosis are very different.

Causes of peripheral vestibular disease include ear infections, idiopathic geriatric vestibular disease, toxins, hypothyroidism, cancer and others.

Causes of central vestibular disease include encephalitis, brain tumors, strokes and others.

A thorough history and general physical examination are performed.  A neurological examination may determine if the problem is localized to the peripheral or central vestibular system.  Blood tests, blood pressure measurement, X-rays, MRI and CSF analysis are useful in determining the cause (and potential treatments) of vestibular disease.  CT scans typically are not sensitive enough to evaluate the central vestibular system.

Treatment and prognosis can vary widely and depend on coming to an accurate diagnosis.  Many causes of vestibular disease carry an excellent prognosis and/or can be managed with medications.

Encephalitis, Meningitis and GME

Encephalitis, meningitis and GME all refer to inflammation of the nervous system.  Encephalitis means ‘inflammation of the brain’, whereas meningitis means ‘inflammation of the meninges’.  Certain breeds are more likely to be affected with encephalitis, including the Yorkshire Terrier, Maltese, Chihuahua, terrier-breeds, and Pugs.  Any age can be affected, but most commonly the pet is a young adult or adult.  There are two broad categories of encephalitis in dogs: infectious causes and non-infectious causes.  Non-infectious causes of encephalitis are much more common in dogs and will be the focus of this article.

The true underlying cause for encephalitis in dogs remains unknown.  There is evidence that encephalitis is due to autoimmune disease.  In a normal dog, the immune system acts to protect the body from infection, etc.  The body relies on the immune system to recognize itself and recognize infections, etc as ‘non-self’.  In autoimmune disease, the immune system loses the ability to discriminate between self and non-self and mounts an inflammatory attack against itself.  Examples of autoimmune disease in people include rheumatoid arthritis and lupus.  In dogs with encephalitis, the immune system attacks the brain and coverings of the brain (meninges).

Clinical signs of encephalitis depend on the part of the brain that is affected, but may include seizures, walking in circles, changes in behavior, seeming off balance, stumbling in the legs, blindness or pain.  Sometimes multiple parts of the brain can be affected, and multiple clinical signs are present.  A complete neurological examination is performed to determine what part of the brain is affected.

Encephalitis can be suspected based on age, breed, history, clinical signs and neurological examination.  However, other neurological diseases may have similar characteristics, and therefore tests are warranted.  Blood tests are useful as a general health screen, but seldom are enough to diagnose encephalitis.  Encephalitis is diagnosed by MRI of the brain and CSF analysis.  Sometimes additional blood tests or CSF tests are warranted to rule out infectious causes of encephalitis.  MRI may show characteristic areas of ‘inflammation’.  CSF analysis may show an elevated nucleated cell count (pleocytosis), with increased protein levels.

High-field MRI of a dog's brain with encephalitis. The arrows show 'hyperintensity' of the white matter on the left side of the screen. Also note that the ventricles (bright white) is asymmetrical.

Encephalitis in dogs is thought to be an autoimmune disease.  Treatment involves medications to decrease the inflammation and suppress the overactive immune system.  Prednisone is often used for this, however, dogs treated with prednisone alone often have shorter survivals.  Recently, ‘newer’ drugs have been studied for use in dogs with encephalitis that may increase survival times.  These medications include cytosine arabinoside, cyclosporine, azathioprine, leflunomide and procarbazine.

Prognosis is guarded in that many dogs respond to medications and have prolonged (years) survivals, whereas others respond to medications but suffer relapses, and some do not respond at all.  An early, accurate diagnosis and aggressive medical therapy is important.

Brain Tumors in Dogs and Cats

Brain tumors are a relatively common neurological problem in dogs and cats and typically affect older pets.  Certain breeds are over-represented including the Boxer dog, Golden Retriever and Boston Terrier.  Clinical signs depend on the location of the tumor, but may include seizures, behavior changes, compulsive circling, weakness, wobbliness, blindness, and balance problems.

Brain tumors may be thought of as primary brain tumors and secondary brain tumors.  Primary brain tumors arise from cells that make up the brain and it’s lining.  Secondary brain tumors arise elsewhere and spread to the brain (metastasis).

Primary brain tumors in dogs and cats may include meningiomas, glioma, choroid plexus tumors, ependymoma, pituitary tumors and others.

Meningiomas are the most common type of primary brain tumor in dogs and cats.  They arise from the meninges (covering of the brain).  They are more common in long-nosed breeds of dogs, such as the Golden retriever.  They tend to be slow-growing and compress the brain from the ‘outside’ in.

Gliomas arise from the supporting cells of the brain (glial cells) and include astrocytomas and oligodendrogliomas.  They are more common in short-nosed breeds of dogs, including the Boxer and Boston terrier.  They tend to grow on the ‘inside’ of the brain.

Clinical signs depend on the location of the tumor, but may include seizures, behavior changes, compulsive circling, weakness, wobbliness, blindness, and balance problems.  There are other neurological diseases that can cause identical clinical signs, and therefore further tests are warranted.  A CT scan may show some types of brain tumors, but MRI is considered the best imaging modality when a brain tumor is suspected.  A biopsy is necessary for a definitive diagnosis.

Treatment of brain tumors depends on the size, location and suspected type of tumor.  Treatment options may include surgery, radiation therapy, chemotherapy, or palliative medications.

Neck Pain, Tetraparesis and Inability to Walk

Cervical intervertebral disk disease may cause a range of clinical signs.  Most commonly, dogs will exhibit signs of neck pain–walking slowly, holding their head low, spasms of the neck muscles, and crying spontaneously.  Some dogs may show weakness (tetraparesis) or wobbliness (ataxia) in all four legs.  Postural reactions may be normal to absent.  Cranial nerves are normal.  Spinal reflexes may be decreased in the thoracic limbs depending on the location of the disk herniation.  A thorough neurological examination is necessary to ascertain the location and severity of the problem.

Intervertebral Disk Disease is a common cause of neurological disease in the dog.  There are seven bones in the canine neck (vertebrae).  Between each vertebrae is an intervertebral disk, which acts as a ‘cushion’ between each bone.  The intervertebral disk is made up of a fibrous outer part, the annulus fibrosus and a jelly-like inner part, the nucleus pulposus.  Intervertebral disk disease occurs when the nucleus pulposus loses it’s jelly-like consistency, becomes dry, and herniates through the top of the fibrous outer part.  Disk herniations often lead to compression of the spinal cord.

Other diseases to consider that may cause similar signs include atlantoaxial instability, meningitis/myelitis, diskospondylitis, tumor, syringomyelia, arachnoid diverticula, caudal cervical spondylomyelopathy (Wobbler’s) and others.

A minimum database of CBC, chemistry and thoracic radiographs should be performed.  Well-positioned cervical radiographs are useful in detecting bony tumors or diskospondylitis, however, they are limited in their ability to visualize the intervertebral disk, the spinal cord, and other soft tissues.  High-field MRI is considered the optimal modality to image the nervous system.  CSF analysis is sometimes warranted.

MRI of the cervical spine showing a herniated intervertebral disk (arrow).

Surgical decompression is typically curative.  Most dogs with a herniated disk in their neck have about a 98% chance of cure when treated with surgery by a qualified neurologist/neurosurgeon.  A ventral slot procedure is often the surgery of choice, but depends on the size and location of the disk herniation.

Ms. A

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