Friday, April 28, 2017

Anemia in Cats

Like every veterinarian, when I’m performing a physical examination, I evaluate the mouth and gums of my patient.  I expect to find nice pink gums, and most of the time, I do.  Occasionally, however, I’ll note with dismay when I lift the cat’s lip, that the gums are pale, or even white.  This finding immediately sets off alarm bells in my head: this cat is anemic. The task of making a diagnosis now begins.

            Anemia is a decreased amount of red blood cells.  It is a laboratory finding, not a diagnosis.  By approaching an anemic cat in a systematic fashion, a definitive diagnosis can be achieved in most cases. 

            Attention should first be paid to the breed and age of the cat. Although cats have fewer breed-related red blood cell disorders compared to dogs, some Abyssinians and Somalis have been reported to have excessively fragile red blood cells, making them prone to anemia.  Young cats, with their small blood volume, are more susceptible to blood-sucking internal parasites like hookworms, or external parasites, like fleas.  Middle aged cats are most likely to develop immune-mediated anemia (see below), while older cats have a higher likelihood of developing kidney disease or cancer, two common causes of anemia (see below).
            Physical examination findings can provide valuable information regarding potential causes for the anemia.  The presence of a fever may indicate an infection or inflammation.  Muffled heart or lung sounds may suggest bleeding into the pericardium (the membranous sac around the heart) or the chest cavity.  An enlarged spleen felt during physical exam might indicate a splenic tumor. One particular splenic tumor – a hemangiosarcoma – frequently bleeds into the abdomen. 

            The most important test to run when assessing an anemic cat is the complete blood count (CBC).  This test measures several important parameters, and provides both diagnostic and prognostic information.  First and foremost, the CBC measures the hematocrit, an assessment of the severity of the anemia.  Other important parameters on the CBC are the MCV (mean cell volume) and MCHC (mean cell hemoglobin concentration).  The MCV is a measure of how large or small the red blood cells are, while the MCHC assesses the amount of hemoglobin in the red cells.  Evaluation of MCV and MCHC can give strong hints as to the possible cause of the anemia.

            The first step in trying to elucidate the cause of a cat’s anemia is to determine whether the anemia is “regenerative” or “non-regenerative”.  A regenerative anemia is one in which the bone marrow responds to the anemia by releasing immature red blood cells, called reticulocytes, into the bloodstream.  These reticulocytes aren’t fully mature, but they can still carry oxygen.  A non-regenerative anemia is an anemia in which the bone marrow is not responding to the blood loss and not releasing reticulocytes in an attempt to replace the missing red blood cells.  Reticulocytes are larger than mature red blood cells, and this is reflected in the MCV; a cat with a high MCV has larger than normal red blood cells.  Reticulocytes also have less hemoglobin in them, which will lower the MCHC.  Thus, a cat with both a high MCV and low MCHC has red blood cells that are larger and have less hemoglobin in them than normal, suggesting the presence of many reticulocytes, i.e., a regenerative anemia.  The true way to determine whether the anemia is regenerative or not is to directly count the number of reticulocytes present. This is something that should be done for all cats with significant anemia. 

            There are basically two main causes for regenerative anemia:  blood loss and hemolysis.  Most causes of blood loss can be identified relatively easily.  Cats with a history of trauma (hit by a car, falling from a height) often suffer blood loss as a result of their injury.  The bleeding may be internal, for example, from a ruptured spleen, or it may be external.  Ultrasound of the abdomen and/or x-rays of the chest may reveal the presence and source of internal bleeding.  External bleeding is usually apparent on physical examination.  If blood loss has been ruled out in cases of regenerative anemia, hemolysis becomes the most likely explanation for the anemia.  Hemolysis is the destruction of red blood cells.  Hemolysis can be either immune-mediated (the cat’s immune system is attacking and destroying the red blood cells) or non-immune mediated.  Immune mediated destruction of red blood cells (a.k.a. immune-mediated hemolytic anemia, or IMHA) is the most common cause of hemolysis in small animals.  In some cases, the immune system is attacking the red blood cells for no obvious cause at all.  This is termed primary hemolytic anemia.  More often, there is a secondary cause for the immune system to attack the red blood cells, such as infection with a virus or a red blood cell parasite, or cancer. Non-immune-mediated hemolytic anemia has a variety of causes, including onion ingestion, snake bite envenomation, severely low blood phosphorus levels, and zinc toxicosis (usually caused by swallowing pennies minted after 1983).

            Non-regenerative anemia may be due to several causes, the most common being some type of chronic illness.  A multitude of inflammatory, infectious, and cancerous disorders can lead to anemia, most cases being of mild to moderate severity.  Infection with the feline leukemia virus often leads to severe non-regenerative anemia. Chronic kidney disease is a very common cause of non-regenerative anemia in cats.  The kidneys produce a hormone called erythropoietin. This hormone instructs the bone marrow to produce red blood cells.  When the kidneys are failing, they often do not produce enough of this hormone, and the bone marrow therefore doesn’t produce enough red blood cells.  Anemia from chronic kidney disease can sometimes be quite severe.

            Treatment of anemia in cats depends on the cause. Cats with life-threatening anemia may need to be stabilized with a blood transfusion.  Like humans, cats have distinct blood types, and it is imperative that the donor and recipient are compatible.  If blood loss was determined to be the cause of the anemia, the reason for the blood loss must be addressed and remedied for treatment to be successful.  Cats with immune-mediated hemolytic anemia are typically treated with immunosuppressive medications so that the immune system stops attacking the red blood cells.  The most common drug prescribed for this purpose is prednisolone.  In stubborn cases, additional drugs may be needed to get the condition under control.
As mentioned above, a common cause of non-regenerative anemia in cats is reduced production of the hormone erythropoietin in cats with kidney disease.  This type of anemia can be treated by giving injections of the hormone erythropoietin under the skin.  In the past, up to 25% of treated cats eventually developed a life-threatening immune reaction to the injection, but a newer form of the hormone, called darbepoietin, is very effective and rarely causes adverse reactions in cats.

            Anemia is a common finding in cats.  Because there are so many potential causes for anemia, making a definitive diagnosis can be a challenge.  By taking a systematic approach, performing a good physical exam, and properly interpreting the complete blood count and other diagnostic tests, most clinicians can clearly elucidate the cause of the cat’s anemia.  Prognosis depends on the cause, as well as the cat’s individual response to treatment.

Saturday, April 15, 2017

Fleas and Flea Control in Cats

Summer is over, and a lot of cats are rejoicing. It may be a fun season for people, but it can be miserable for cats, because warm and humid weather is paradise for fleas.  Few creatures living on Earth today have had as much impact on world history as the common flea.  From the black plague during the 14th century to the present, fleas have been the cause of much grief. 

            To better understand how fleas torment cats and humans, and how best to combat them, it is important to understand the life cycle of the flea.  Once a flea jumps on a cat, it stays there for its entire life.  Contrary to popular belief, fleas do not jump from one cat to another. Although the flea spends its entire life on the cat, the majority of the flea’s life cycle occurs while off the cat.  When a female flea hops on a cat, it begins feeding on blood within minutes.  Ingestion of blood is required for the flea to be fertile and reproduce.  Approximately 24 hours later, the flea begins to lay eggs, about 40-50 per day.  As the cat moves around the house, it acts like a living salt-shaker, disbursing the flea eggs in the environment, mainly in the areas where the cat sleeps or rests.  Within a week, larvae hatch from flea eggs. The larvae try to avoid light and burrow into carpets, cracks in hardwood floors, and other humid areas such as concrete floors in damp basements.  Five to twelve days after that, larvae spin a cocoon in which they develop into pupae. One to three weeks later, baby fleas emerge from pupae.  These newly hatched fleas wait for the cat to pass by, and then they hop on, and the life cycle starts all over again. The entire flea life cycle takes 3 to 6 weeks.  If you were to assess all of the life stages of the flea as a population, adult fleas comprise only about 5 per cent.  Eggs make up 50% of the population, with larvae at 35% and pupae at 10%.  In other words, if you’re seeing adult fleas on your cat, you can be sure that there is a veritable flea factory looming nearby. Even if a cat spends its entire life indoors, it is not immune from these pesky critters.  Fleas are hitchhikers – they jump onto your clothing, and you bring them back home, where they hop onto your unsuspecting cat.

            At best, fleas can make your cat itchy and uncomfortable.  At worst, they can transmit dangerous diseases.  While dogs usually bite or scratch at fleas, cats use their barbed tongues to remove them, often abrading the skin in the process. The most prevalent skin disorder in small animals is flea allergic dermatitis (FAD). This is more than just a mechanical irritation from the flea.  When fleas bite the cat, they deposit their saliva into the skin before ingesting blood.  Proteins in the flea saliva can induce a hypersensitivity reaction in some cats.  This allergic reaction causes severe itching, and cats often develop small crusty papules and hair loss on their neck and face, and most notably down their back, in the classic “racing stripe” pattern.

            Fleas are responsible for transmitting tapeworms to cats. Heavily parasitized cats, especially kittens, can develop anemia due to blood loss from flea bites.  Fleas also transmit Bartonella, the organism responsible for cat-scratch disease in humans.  Most cases of cat-scratch disease are self-limiting, however, Bartonella infections can cause very serious illnesses in people with immune deficiency disorders. Fleas can also pass Bartonella from one cat to another.  Most cats infected with Bartonella are clinically normal, however, infection in cats can sometimes lead to fever, lethargy, lymph node enlargement, eye inflammation, and other disorders in cats.                
            Because some of the infectious agents transmitted by fleas may affect humans, the American Association of Feline Practitioners recommends year-round flea control.  Historically, the most effective approach was the three-step method:  treatment of the yard, home, and cat.  The newer flea and tick control products, however, are so effective that treatment of the premises is rarely necessary, especially if the cat resides totally indoors.

            Fleas sprays, flea dips, and flea shampoos have become obsolete.  Flea control is now achieved through the use of products that are either given orally or topically once a month.  Some of these products are effective not only against fleas, but other parasites as well, including ticks, heartworms, ear mites, hookworms, and roundworms. 

            A variety of flea control products are available to cat owners. Common products include those that contain either imidacloprid (Advantage), fipronil (Frontline), dinotefuran (Vectra), spinetoram (Cheristin) or selamectin (Revolution).  These products are applied to the skin on the back of the neck.  They  sink into, and then spread through, the layer of fat beneath the skin, killing any adult fleas that are present on the cat.  The advantage of these products is their residual activity; they continue to kill fleas for at least thirty days.  After 30 days, a new dose is applied.  These products are very safe, and very effective.   Oral flea control products are also available. Nitenpyram (Capstar) is an oral medication that is good for heavy flea infestation.  A single oral dose of nitenpyram will kill all of the adult fleas on a cat. It starts to work within 30 minutes of administration.  Nitempyram has no residual effect, so if the cat gets re-infested with fleas, an additional dose may be required.  It can be given safely as often as every day.  Nitenpyram can be used together with other flea products.  Spinosad (Comfortis) is an oral formulation that kills 100% of adult fleas on a cat by 24 hours after administration.  Spinosad has residual effect; it continues to kill adult fleas for 30 days before the next oral dose is required. Lufenuron (Program) is an insect growth regulator – a product that works by interfering with the growth and development of fleas, but has no effect on adult fleas.  It is given orally once a month, however, an injectable form is available that is effective for six months.  When a female flea ingests blood from a cat treated with lufenuron, the eggs she produces will be infertile.  Because lufenuron does not kill adult fleas, it is better suited to prevent a continual flea problem.  It does not stop a flea from biting, so it is not ideal for cats with flea allergic dermatitis.  If quicker results are needed, a product that kills adult fleas should be used.

            For cat owners who prefer to use flea collars, there is a collar (Seresto) that contains a sustained release formulation of the flea-killing compound imidacloprid, in combination with flumethrin, which kills ticks.  The collar kills fleas and ticks for 8 months, reducing the need for monthly application of topical products. The collar also has a “break-away” mechanism, so if it gets caught on something, it will release, rather than cause injury to the cat. 

            Cat owners should be aware that in an effort to tap into the lucrative flea-control market, some manufacturers have produced flea control products with packaging similar to the veterinary products, i.e. in small, single dose tubes for topical application.  These products contain permethrin, an insecticide commonly found in low concentrations in a variety of canine and feline flea sprays and shampoos.  In low concentrations, cats tolerate these products with minimal adverse effects.  These small single-dose tubes, however, contain concentrated permethrin (45% to 65%) as the active ingredient.  Concentrated permethrin spot-on products are labeled for use in dogs only, and may cause severe and often fatal toxicosis if applied to cats. 

            Fleas have been a source of much misery for pet cats and dogs. They can transmit diseases to cats, as well as to humans.  Fortunately, modern flea control products can provide an amazing level of efficacy. Understanding the flea life cycle is critical in formulating a comprehensive flea-and-tick control strategy.  Talk to your veterinarian about which products are right for you, as different products offer different benefits.  Be aware, however, that improper use of these products can result in treatment failure, and use of unsuitable or mislabeled products can have dire health consequences.

Monday, April 3, 2017

Body Parts - The Feline Brain

Body Parts – The Brain

            The brain is the main organ that comprises the central nervous system of the cat.  It is the control center for receiving and interpreting information that comes from the cat’s own body, and from the outside world.  Learning and perception takes place in the brain, and all of the sensations – sight, sound, smell, taste, touch, and pain – are processed through here. I’ve been a veterinarian for over 28 years, and despite examining and treating thousands of cats, I’ve come to accept one thing for certain: I will never truly understand the feline brain.  (I do enjoy trying, though.)

            The brain is a lump of spongy pink nerve tissue located within the skull. It can be divided into three major parts: the cerebrum, the cerebellum, and the brainstem.  The cerebrum makes up the majority of the brain tissue. It can be divided into two major portions: the right cerebral hemisphere, and the left cerebral hemisphere.  The hemispheres are connected to each other by a piece of tissue called the corpus callosum, which allows messages to be transported from one side to the other.  The cerebellum is found at the back of the brain, attached to the cerebrum.  It is responsible for physical coordination, balance, and posture.  The brainstem is located at the base of the brain. It regulates important functions such as blood pressure, breathing, and heartbeat.  The brain is covered with several membranes, called meninges.  A fluid, called cerebrospinal fluid, is found beneath the meninges, bathing the brain and protecting it from injury.

            Like any other organ, the brain may become diseased or disordered.  The list of potential brain disorders is pretty long: infections, inflammations, hereditary disorders, metabolic disorders, toxic conditions, tumors, and trauma, to name a few.   A few of the more common ones I encounter as a feline practitioner include seizures, cerebellar hypoplasia, and brain tumors.

            Seizures occur when neurons in the brain begin to fire all at once, in an uncoordinated fashion. Seizures are seen less commonly in cats compared to dogs.  Seizures can be divided into primary seizure disorders and secondary seizure disorders.  Primary seizure disorders are those for which there is no underlying cause.  This is better known as epilepsy.  In dogs, there tends to be a genetic basis for epilepsy, but this doesn’t seem to be the case in cats.   Secondary seizure disorders are those for which there is a known cause.  The list of disorders that can cause seizures in cats is extensive, and includes infections (such as feline leukemia virus and toxoplasmosis), metabolic disorders (low blood sugar, low blood calcium, liver disease, thiamine deficiency), brain tumors, toxins (lead, antifreeze) and trauma.  In most cases of secondary seizures, if the cause is addressed, the seizures will resolve.  Cats with epilepsy may require anticonvulsant medication, depending on the frequency and severity of the seizures.  The most commonly prescribed anticonvulsant is phenobarbital.

            As noted above, the cerebellum is responsible for coordination and fine motor skills in the cat.   Cerebellar hypoplasia is a condition in which a kitten is born with an underdeveloped cerebellum at birth.  The most common reason for this is an infection with the feline panleukopenia virus while the mother is pregnant.  Affected kittens will have mobility issues as a result.  The severity of the condition varies from cat to cat, even among littermates.  Some cats are mildly affected, while others really have difficulty getting from point A to point B.  These cats may also have head tremors, sometimes called “intention tremors” because they’re more pronounced when the cat is deliberately intending to do something with its head, like eat or drink.  Although cats with cerebellar hypoplasia may look like they’re struggling, we should bear in mind that these cats have no idea that they’re any different from other cats.  Because they were born this way, they think they’re normal.  The condition is not painful, and it is not progressive – it won’t get worse over time.  There is no treatment for cerebellar hypoplasia, and there really is no need for one.  What these cats lack in mobility, they make up in personality. 

            Sadly, just like any other organ, the brain is also susceptible to cancer.  Brain tumors may be classified as primary or secondary.  Primary brain tumors are those that arise from cells found within the brain or the membranes surrounding the brain.  Secondary brain tumors are those that have metastasized (spread) to the brain as a result of a primary tumor elsewhere in the body.  The clinical signs of a brain tumor can vary and include abnormal mental status or behavior such as stupor, head-pressing (the cat relentlessly presses its head against a wall or other surface), walking in circles, or seizuring.

The three main treatment options for brain tumors are surgery, radiation, and chemotherapy.  Surgical removal of the tumor is rarely attempted, although meningiomas (tumors arising from the membranes that cover the brain) are sometimes surgically amenable.  The goal of chemotherapy and/or radiation is to reduce the size of the tumor and control the symptoms.  The prognosis for cats with brain tumors is poor.


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