Oddball neurologic disorders: dogs (Proceedings)

Canine Epileptoid Cramping Syndrome (Spike's disease)

This is a poorly characterized problem in Border Terriers that may be a metabolic, neurological or muscle disorder! It may previously have been confused with canine epilepsy. Owners or breeders of the affected dogs have indicated that many affected dogs become asymptomatic through dietary changes. One factor that has contributed to the obscurity of this problem is that some of the cases involved only one or a few episodes.

Signs have varied: staggering, dizziness, exaggerated stretching, unusually slow and/or methodical posturing or walking, trembling, abdominal and lumbar muscle contractions, borborygmus and apparent intestinal pain, falling over, struggling to rise but unable to do so. Dogs are cognizant, responsive to stimuli.

Age of onset: Apparently any. But 2-6 years seems to be the average.

Frequency of episodes: varies from 1-2 x during the animal's lifetime to several times per week. In some dogs, signs are progressive in frequency and duration.

Dancing Doberman Disease

Dancing Doberman syndrome is poorly understood, but it is probably a peripheral neuropathy. The etiology is unknown. Thus far, it has only been described in Doberman pinschers with an age range of 6 months to 7 years. Signs are first observed in one hind limb and consist of flexion of the limb while standing. Similar signs then usually develop in the other hind limb, resulting in "bicycle" type motions when dog is standing: one hind leg flexes, is put down, and the other one flexes. Pain is not present. Oddly enough, pelvic limb spinal reflexes are often increased, rather than decreased, as one would expect for a peripheral neuropathy. Over months to years, clinical signs usually continue to progress to encompass proprioceptive deficits and paraparesis. In one case that was followed for 5 years, quadriparesis developed suggesting that the disease may progress to the thoracic limbs as well.

Needle electromyography is abnormal with positive waves, fibrillation potentials, and complex repetitive discharges (bizarre high frequency discharges) in the gastrocnemius muscle. Electromyographic changes also develop in front limb muscles. Muscle biopsy results have shown mild myofiber atrophy.

There is no treatment and signs do not resolve.

Sleep-associated Movements

Alternating phases of brain activity occur during sleep. The first stage of sleep is characterized by low frequency electrical activity, i.e. slow wave sleep. This is followed by rapid eye movement (REM) sleep. In people, REM sleep is characterized by rapid eye movements, irregular breathing, increased blood pressure, and loss of muscle tone. However, the brain is highly active, and the electrical activity recorded in the brain by EEG during REM sleep is similar to that recorded during wakefulness. REM sleep is usually associated with dreaming in people. Slow wave sleep alternates with REM sleep in cycles lasting about 20 minutes.

During REM sleep, animals will often groan or whimper slightly and move or twitch their limbs or face. This may occasionally be confused with a seizure or other abnormality. If the movements are sleep related the dog will wake up normally when it is awakened.

In some animals, the movements during sleep are abnormally excessive, even violent. Some dogs or cats may lift their head and propel themselves across the floor. Some have excessive running movements of the limbs. Some may attack inanimate objects or whatever is in their path if they are moving forward. In contrast to a seizure, dogs can be aroused during these episodes and awake with no confusion or incoordination. We think that these signs are similar to a sleep disorder in people called REM behavior disorder. Clonazepam is often successful at reducing the problem in affected dogs and people.

Fly Biters

Fly-biting behavior, in which the dog appears to be snapping at an imaginary fly, is seen in dogs, especially Caviler King Charles spaniels, miniature Schnauzer, and greater Swiss mountain dogs. Fly-snapping behavior has traditionally been thought to be a form of psychomotor epilepsy but it may also be a form of obsessive-compulsive disorder.

Seizure: In cases where the signs are due to seizure activity, there may be pre-ictal and post-ictal stages (lethargy, disorientation). These are likely complex partial seizures or seizures originating from the visual cortex. In people, visual cortical seizure activity can cause spots of light or other visual hallucinations. Some affected dogs seem to be following objects with their eyes and ears. Definitive diagnosis is based on finding EEG abnormalities or response to anti-seizure medications. A thorough neurologic exam is also important to identify any focal brain lesions that would indicate the need for imaging and CSF analysis to r/o a progressive brain lesion. Many patients respond to anticonvulsants.

Compulsive disorder: Fly-snapping is considered to be compulsive when the bouts are frequent, disruptive to the animal's functioning, continue for prolonged periods of time, are associated with anxiety, and there is no aura or other symptoms compatible with a diagnosis of psychomotor epilepsy.

Metronidazole Toxicity

Metronidazole is postulated to act at the GABA receptor in the cerebellum and vestibular systems. Doses of greater than 60mg/kg/day have been associated with severe cerebellar and central vestibular signs in dogs. But doses as low as 30mg/kg/day have been known to cause CNS signs. Seizures can occur but are more common in cats administered doses of greater than 48mg/kg/day. Discontinuation of the drug usually produces a rapid improvement, but dogs with metronidazole toxicosis recover faster (13.4 hours compared to 4.25 days for non-diazepam treated dogs) when treated with diazepam for 3 days at a dose rate of 0.2-0.6mg/kg q8hr. The exact mechanism by which diazepam exerts its favorable effect in reversing signs of metronidazole toxicity is not known but is likely related to GABA receptor dysfunction within the cerebellar and vestibular systems (postulated that diazepam competitively displaces metronidazole from the benzodiazepine sites on the GABA receptors).

Chiari Malformations (Syringomyelia, Caudal Occipital Malformation Syndrome)

Chiari malformations are developmental disorders of the occipital bone mesoderm, most likely genetically transmitted. Dysplasia of the occipital bone results in a malformation of the caudal fossa causing crowding of the structures of the caudal fossa. The end result is herniation of the cerebellar tonsils with compression of the underlying brain stem, and syringohydromyelia in the cervical spinal cord. Syringomyelia refers to abnormal cavities filled with liquid within in the substance of the spinal cord. A "syrinx" refers to one of these cavities. Hydromyelia refers to a pathologic condition characterized by accumulation of fluid within an enlarged central canal of the spinal cord. In both of these instances, the fluid that accumulates is similar, if not identical, to cerebrospinal fluid (CSF).

Chiari malformations, first recognized in the Cavalier King Charles spaniel, are now being recognized in many different toy breed dogs. Oddly enough, the primary initial clinical sign is scratching at the neck or shoulder area. This is believed to result from compression of the decussating spinothalamic tracts within the spinal cord by the syrinx. As the lesion progresses, other signs such as ataxia, weakness and neck pain develop in some patients.

Diagnosis is by MRI of the caudal fossa and cervical spinal cord. Initial treatment for mild cases has been glucocorticoids and/or gabapentin. Foramen magnum decompression (FMD) procedure may allow the discontinuation of life-long steroids.

Limber Tail (Cold Tail)

This is a condition in which working dogs (Pointers, Labrador Retrievers, coonhounds, beagles, golden retrievers) suddenly develop a flaccid tail. The tail either hangs down from the tail base or is held out horizontally for several inches from the tail base and then hangs straight down or at some degree below horizontal. Sometimes the hair on the dorsal aspect of the proximal tail may be raised. Affected dogs may resent palpation of the area 3-4 inches (8-10 cm) from the tail base.

Some affected dogs have a history of prolonged cage transport, a hard workout the previous day, swimming, or exposure to cold or wet weather.

Mild elevation of serum creatine kinase may be found early after onset of clinical signs. Abnormal needle electromyographic changes (spontaneous discharges restricted to the coccygeal muscles) are found several days after onset. There is histopathologic evidence of muscle fiber damage. Specific muscle groups, namely the laterally positioned intertransversarius ventralis caudalis muscles, were affected most severely. Abnormal findings on thermography and scintigraphy further support the diagnosis of muscle damage.

Most dogs recover spontaneously within a few days to weeks. Anecdotal reports suggest that anti-inflammatory drugs administered within 24 hours after onset hasten recovery. Less than one half of affected dogs experience a recurrence. Most owners and trainers familiar with the condition do not seek veterinary assistance. Other conditions that have been confused with "limber tail" include tail fracture, spinal cord disease, and impacted anal gland.

Myxedema Stupor and Coma

Myxedema coma is an uncommon and severe form of hypothyroidism. A concurrent illness or predisposing factor (infection, central nervous system depressants, stress, trauma, cold exposure, diuretics) may result in decompensation of chronic hypothyroidism. A reduction of oxidative processes and slowing of metabolism in all body systems causes lethargy progressing to stupor, coma, and if untreated, death.

The typical signs of hypothyroidism are accompanied by some combination of myxedema (nonpitting edema of the face and jowls); obtundation, stupor, or coma; hypothermia often without appropriate shivering (rectal temperature may be in the 70s or 80s); bradycardia (heart rate may be as low as 20-30 bpm); hypotension; and hypoventilation. Because of the life-threatening nature of this illness, a presumptive diagnosis should be made and appropriate therapy instituted pending results of thyroid function tests.

Treatment consists of levothyroxine (a single IV dose that is 3-5 times the standard oral dose is usually recommended, followed by standard oral doses). Supportive care consists of passive warming. Fluid administration should be judicious because of impaired free water excretion.

Hypothyroidism should always be an initial rule-out for hypothermia without obvious cause. If the hypothermia is present without efforts to shiver, hypothyroidism should be suspected until proven otherwise.