Diseases #7
Cataracts are very common in dogs but not so in cats. A cataract is defined as a cloudiness or opacity to the lens of the eye. It is often confused with nucleur sclerois of the lens in the middle aged dog which produces a graying of the lens area in both the left and right eye at the same time. Cataracts can be juvenile (congenital or acquired early), pathological (secondary to Diabetes Mellitus) and senile (cataracts that develop in older dogs and very old cats.
When cataracts start to form, the affected lens in the eye takes on a milky like appearance. Over time, the cataract matures and the animal can lose sight in the eye. Dogs depend upon their sense of smell much more than they do vision. Dogs have limited color differentiation and are near sighted to begin with. Loss of vision in the dog is usually not too problematic. In the cat, senile cataracts can cause cats to not jump to places that they were accustomed to. Untreated cataracts can also "float away" elsewhere in the eye. This prevents drainage of eye fluid and can cause build up of intraocular pressure leading to glaucoma.
Many times a dog or cat do not show any clinical signs. Immature cataracts still allow the dog to see pretty well. Only than, when the cataract matures do they cause problems. Even than, if the other eye is not as advanced, the dog can adapt to even mature cataracts. When both are mature, an animal will start to bump into things and become startled when pet or stroked. Signs of blindness begin. Cats rarely suffer from cataracts until they are 15 years of age and up. By that time they are pretty feeble and often are not as active hence cataracts do not seem to bother them.
If suspecting cataracts originating from metabolic conditions such as Diabetes Mellitus, it is crucial to perform a CBC, Blood Chemisty Panel and a urinalysis.
Diagnosis of cataracts involves getting a good history and performing a detailed physical exam. The latter includes an in depth study of the eyes with an opthalomoscope. The eye is able to be studied from the cornea to retina.
There is no medical treatment associated with juvenile or senile cataracts. Those dogs diagnosed very early with diabetes mellitus are spared the development of severe diabetic cataracts. Cataract formation in these cases is proportionate to the amount of time the dog remains in a undiagnosed diabetic state. Juvenile and senile cataracts may be surgically removed and implanted with a spring fitting lens implant.
The prognosis for dogs and cats with cataracts is very good. Since dogs do not depend that much on visual acuity compared to the sense of smell, they do fine with cataracts as long as furniture is not rearranged and no sudden movements are made to touch the pet. Cats are very old when they get cataracts. Supplanting a favorite jumping spot with an ottoman can split the difference in height, making it easier for a cat to jump.
Cushing's Syndrome is a debilitating disease seen in dogs that is caused by excess cortisol (the body's intrinsic cortisone) formation in the adrenal cortex of the animal. Cushing's Syndrome is caused by either a pituitary tumor (90% of the time) a tumor of the adrenal gland or by taking oral corticosteroids for a prolonged period of time (iatrogenic). Cushing's Syndrome is most commonly seen in: Boston Terriers, Poodles, Bichon Frise, Dachshunds, Miniature Schnauzers and other small dogs. About 10% of canine diabetics develop Cushing's Syndrome. Having to administer excess insulin to maintain a relatively stable blood glucose is a sign of something else going on. Insulin resistance is also a possibility but easy to differentiate from Cushing's.
When Cushing's Syndrome is in full swing, excess cortisol is running rampant in the animal's body. On one side, it is immunosuppressed leading to more frequent bladder infections. On the other, the pituitary gland secretes excessive amounts of ACTH that stimulates the adrenal glands to produce excessive amounts of cortisol. This mechanism explains the majority of clinical signs in the dog. Cushing's Syndrome is rarely seen in cats.
Clinical signs of Cushing's disease are distinct in each case. All cases do not share the same clinical signs. The appetite increases. Some dogs have an increased thirst, some do not. The majority will have a pot belly appearance over the abdomen due to an enlarged liver and cortisol's effect of thinning the rectus musculature over the lower (ventral) abdominal wall. Animals may also urinate more and have more frequent bladder infections. Dogs are also much more lethargic than normal. Other clinical signs are associated with the skin. Hyperpigmentation, frequent staphylococcus pyodermas plus calcinosis cutis are usually seen. In advanced cases central nervous signs are seen due to the enlargement of the pituitary gland. Head pressing is the most commonly seen sign but some animals may also seizure.
The most commonly used test to diagnose Cushing's Syndrome is the ACTH Stimulation Test. The results of the test often do not conclusively diagnose the condition even though all the clinical signs are present. Waiting a month and retesting is often advisable. Dogs that had been treated for some allergy or atopic dermatitis with corticosteroids will not produce accurate results. The only safe corticosteroid that can be used clinically, without altering the true results, is dexamethasone. A CBC and Chemistry Profile are also used to check liver function and electrolyte levels as well as the sodium/potassium ratios.
Diagnosis of Cushing's Syndrome is made by the history and physical exam findings as well as the results of the ACTH Stim Test. Rule outs must be done to rule out Diabetes Mellitus and other diseases that cause an increase in thirst or urination. A diagnosis is facilitated if the veterinarian understands the breeds of dogs most commonly associated with the disease.
There are three forms of Cushing's Syndrome and they are treated differently.
1. Pituitary dependent: Dogs are treated with either Lysodren® or the newer drug, Vetoryl® (trilostane). Both are very good at treating the condition. Lysodren® does have side effects such as an upset stomach but can be managed with 5mg of prednisone several times per week.
2. Adrenal Tumors: Adrenal tumors are surgically removed to treat this condition. If surgery is not available, management can be attempted by using the above listed drugs.
3. Iatrogenic Cushing's Syndrome: The offending oral or injectable corticosteroids have to be stopped. This is difficult because without corticosteroids a medical condition could worsen. With exogenous corticosteroid therapy, the adrenal glands stop making glucocorticoids. If corticosteroids are suddenly removed, the animal may go into shock. For this reason the animal must be tapered off of steroids over a long period of time. The adrenal cortex also produces mineralocorticoid agents, the most common being aldosterone which is needed for sodium regulation. This sometimes is needed to be added to the therapy via Percorten® injections every 26 days.
The prognosis for the majority of Cushing's Syndrome patients is very good if diagnosed early. The most important determinant of clinical success is client education. It is crucial that dogs get regular medical checkups. In the beginning, the ACTH test is done every 2-3 months to check adrenal function plus other pertinent lab work and a physical exam. Most dogs need to be on appropriate medication life long. The disease is never cured but controlled. Most dogs feel so much better and have a great quality of life. Even those animals need to have blood work done at least twice a year. The most important take away point is to regulate the dog as quick and as best as possible. By bringing excess cortisol under control, the iso- enzyme of alkaline phosphatase (a liver enzyme) is inhibited or slowed. It is this inhibition that will slow down the growth of the pituitary tumor decreasing the chances of central nervous system signalment.
The eyelids of a dog or cat serve as an effective windshield wiper and wiper fluid cleaner of the cornea or front surface of the eye. By blinking of the eye and subsequent tear production, irritants and other small debris are effectively removed from the eye. The third eyelid is another effective cleaner of the eye. Behind it is a nicatating gland. It is this gland that prolapses over the third eyelid giving it a beet red oval appearance in the corner of the eye. The cause is a weakening in the connective tissue that normally anchors the gland behind the third eyelid. Cocker Spaniels, Beagles and Lhasa Apsos are the most commonly seen breeds with this condition.
Once the connective tissue anchoring the gland is weakened, the gland will prolapse or push over the third eyelid of the eye. It may occur in both eyes at the same time but is most commonly seen in one eye. Sometimes the other eye is not effected but in other cases the other eye has a Cherry eye months later! This growth is not painful or life threatening. Some gland prolapses can irritate the corneal surface but most dogs do not make a fuss about it.
Cherry eye is most commonly seen in young animals. Most dogs do not demonstrate any clinical signs. Some animals may have slight corneal irritation or a secondary bacterial conjunctivitis.
There is no specific lab test involving Cherry Eye. A CBC and Chemistry profile will probably be done since the repair is performed under a general anesthetic. I usually stain the corneal surface with Fluorescein strips to make sure there is no corneal irritation present.
The diagnosis is made by visualizing the cherry eye in a young dog; particularly in Beagles and Cocker Spaniels.
The majority of dogs with Cherry Eye show no clinical disease and it does not bother them or interfere with their lives. Most repairs are cosmetic, as most owners do not want to look at a piece of red tissue at the corner of their pets eye. Year ago, treatment was the surgical excision of the gland. This has lately fallen out of favor. Animals having had that surgery had problems associated with keratitis sicca (dry eye). Now a days, the gland is surgically tacked down behind the third eyelid. About 10% of those may reoccur. Since the other eye may act the same in the future, some veterinarians recommend that both eyes be done at the same time.
The prognosis for all cases of Cherry Eye is good as long as the gland is surgically tacked down.
The cause of Cheyletiella in dogs is a mite that lives off of cellular debris on the surface of the skin.
Cheyletiella is highly contagious. It is transmitted by direct to direct skin contact between dogs. They live on the skin producing dandruff and severe pruritus (itch) usually in young animals. Dogs and cats can get this parasite. It can be transmissible to humans even though humans are not a natural host. The parasite causes the greatest damage in young animals that have an immature immune system and transmitted easily in places where dogs are kept in close quarters such as animal shelters, pet stores and groomers.
The main clinical sign in pets is a severe itch and inflammation of the skin surfaces. Secondary bacterial infections may also occur. Much of the pruritus seems to be along the back of the animal. It is characterized as "walking dandruff disease". The mite is pushing around dandruff and other debris and it appears that the dandruff is walking through the dogs coat.
In some cases, Cheyletiella can be seen crawling around with the naked eye. It is much easier to take a piece of tape, apply it to the skin than look for the parasite under a low magnifying objective microscope lens.
A diagnosis of Cheyletiella is made by observing the small yellow parasite directly on the skin or via a microscope. Also noting if the animal is young and has been around other animals in close quarters is helpful.
Many preparations that kill fleas also work killing the Cheyletiella mite. Simple sprays that contain pyrethrins can work but it is much more effective to use more modern products that are easier to administer. Selamectin (Revolution®) and milbemycin (Interceptor®) are good choices. If there is more than one pet in the household, all should be treated. Combs and pet brushes should be discarded and all bedding and pet blankets should be thoroughly cleaned and disinfected. Since humans are not the natural host, any parasites found on people will disappear upon removing them from the pets and environment.
The prognosis for the treatment of the Cheyletiella mite is excellent. However, the animal can be exposed to the same parasite over and over from infested animals that it comes into contact with.
Chocolate is irresistible to most people. It is also irresistible to most dogs. In people, it leads to excess calories and weight but it is toxic to dogs. Chocolate contains cocoa bean derivitives. The most toxic to dogs are theobromine and caffeine.
All chocolate is not created equally plus the chocolate toxic dose is different for a small animal compared to a large dog. Toxicity is based on mg/kg of theobromine or caffeine. Milk chocolate has a relatively low level of theobromine. Semi-sweet chocolate, which is used often on chocolate chip cookies as nuggets, has more toxic components than milk chocolate. Baker's chocolate is the worst for pets as it contains toxic chemicals in the highest concentration compared to the other chocolates.
Clinical signs are based upon the amount of chocolate ingested and the type of chocolate. Early signs of irritability, pacing and nervousness are present. Toxicity of chocolate and bulk volume can cause vomiting and diarrhea. In more advanced cases the heart and respiratory rate increase and excess neurological stimulation can lead to seizures. Cardiac arrythmias can also arise.
Pertinent lab work is a CBC and Chemistry profile plus an electrocariogram to note if any heart arrythmias are present. Levels of theobromine in the blood can be assessed by an independent lab.
Diagnosis is made easily when the owner sees a pet ingesting chocolate or an empty chocolate wrapping. The history is extremely important. It can be difficult to actually diagnose if no one saw the chocolate ingested. A doctor can only than treat the clinical signs.
The treatment for chocolate toxicity varies on the type and quanity of chocolate ingested. If caught early, the animal is made to vomit with subconjunctival doses of apomorphine or an appropriate dose of hydrogen peroxide. This is followed up by multiple doses of activated charcoal. This treatment will eliminate as much theobromine from the stomach plus delay or prevent the absorption of theobromine into the general circulation. Advanced clinical signs require intravenous fluids to diurese the animal; ridding it of as much theobromine as possible. Excessive heart rate may need to be slowed by beta blockers or Ace inhibitors such as benazepril.
The prognosis for rapidly diagnosed and treated chocolate toxicity is very good. The prognosis is much more guarded when neurological signs and arrythmias are present. A more favorable prognosis for those cases occurs when the cardiac and neurological signs subside.