Tuesday, January 24, 2017

Body Parts - The Feline Spleen

Body Parts – The Spleen



Ask most people what their cat’s heart does, and they’ll tell you it pumps blood.  How about the lungs?  They breathe in oxygen and exhale carbon dioxide.  The kidneys? They filter toxins from the blood stream and put them in the urine.  The spleen?  That’s easy.  It… it… 

Admit it: you have no idea what the heck your cat’s spleen does.   Don’t be embarrassed.  You’re in good company.  The average person is clueless about all things splenic.   I think it’s time we shed a little light on this most puzzling of organs.


Here are the basics:  The spleen is a dark red organ that looks like a giant tongue.  It is longer than it is wide, and is covered by a thick fibrous capsule.  It is located near the stomach, on the left side of the body, however, the exact location of the spleen isn’t fixed.  Depending on its size and shape and the size of the surrounding organs, the spleen can migrate around the abdomen and visit the right side of the body.

The spleen performs a surprisingly large number of functions.  For the sake of clarity, I’ve narrowed down what I think are the four most important splenic duties:

·      Production of red blood cells.   Most people probably know that the bone marrow is the primary site of red blood cell production.  Well, the spleen is the next major site.
·      Storage of red blood cells.  The spleen holds a fair amount of blood.  If the body was suddenly in need of extra red blood cells in the circulation, the spleen has the ability to contract, releasing red blood cells into the bloodstream.
·      Filtration.  Think of the spleen as a giant filter that traps and removes old or abnormal blood cells from the circulation
·      Immunity. The spleen traps bacteria, foreign proteins, and other microbes and presents them to cells in the immune system, so that an immune response can be initiated. 

You’d think that with all of these important roles, the spleen would be essential for life.  Surprisingly, it’s not.  It can be surgically removed if necessary, and most animals will be fine.  However, it’s certainly better to have one than to not have one.

Disorders of the spleen are much more common in dogs than in cats.  Splenic disorders can be generally categorized as either primary or secondary.  A primary splenic disorder is one in which the spleen itself is the site of the illness.  The spleen can also be affected secondarily by a systemic disease that is occurring somewhere else in the body.

How do we know when something is amiss with the spleen?  When things go awry, spleen-wise, the spleen usually grows bigger.  Enlargement of the spleen is called splenomegaly.  This is not something a cat owner would be able to detect.  Splenomegaly is usually found during the physical examination, during the part of the exam where the veterinarian carefully presses on the abdomen to feel the internal organs.

Splenomegaly occurs in two forms: localized and generalized.  Localized splenomegaly is where one focal area of the spleen is enlarged.  We call the enlarged part a “splenic mass”.  Generalized splenomegaly is a diffuse enlargement of the entire spleen.  Localized splenomegaly is more common in dogs.  Generalized splenomegaly is more common in cats.

Once splenomegaly is discovered on examination, your veterinarian will recommend some diagnostic tests to help determine the cause.  Blood tests and x-rays may provide important information.  Abdominal ultrasound, however, is an excellent, non-invasive procedure to distinguish localized vs. generalized splenomegaly, and to further define the condition.  In most cases, however, a definitive diagnosis can only be achieved by obtaining a sample of cells from the spleen for analysis.  The sample is usually acquired via fine needle aspiration, a procedure in which a needle, attached to a syringe, is gently inserted into the spleen. Material is then aspirated into the hub of the needle and the contents sprayed onto a microscope slide.  The slide is evaluated by a clinical pathologist.  If this does not yield a diagnosis, abdominal exploratory surgery may be warranted. 

Sadly, infiltration of the spleen with cancer cells is the most common cause of splenomegaly in cats.  The most common cancer affecting the feline spleen is mast cell tumor.  Hemangiosarcoma (a very bad tumor; my cat Crispy died of this tumor) is the next most common, followed by lymphosarcoma. 

Fortunately, disorders of the spleen are much less common in cats, compared to dogs.   When they do occur, the prognosis will vary, depending on the cause.










Friday, January 13, 2017

Body Parts - the Feline Heart





Body Parts – the Feline Heart



            The heart is the main organ in the circulatory system.  Its job is to pump blood throughout the body, supplying oxygen and nutrients to the tissues.  Similar to the human heart, the feline heart has four chambers.  The two chambers on the top of the heart are the atria (plural for atrium).  The two chambers at the bottom of the heart are the ventricles.  The left atrium and left ventricle are separated from the right atrium and right ventricle by a dividing wall called the septum.



            Listening to your cat’s heart with the stethoscope is one of the most important parts of the veterinary exam.  The normal heart rate in a cat is 160 to 240, which is much faster than a human’s.  Cats are often nervous during the veterinary visit, so it’s not unusual to find heart rates in the 200’s.  The rhythm should be regular and the heartbeat should be easily heard.  Abnormalities in the heart rate and rhythm are fairly uncommon.  The most common abnormality heard with the stethoscope is a heart murmur.  A murmur is the sound of turbulent blood flow and may be an indicator that something is amiss.

            Coronary artery disease is the most common cause of death in humans in the U.S.  Fortunately, cats don’t get coronary artery disease. Nature, however, doesn’t play favorites when it comes to other heart diseases, and cats are indeed susceptible to disorders of this vital organ.  Therefore, the discovery of a heart murmur during your cat’s physical examination warrants further investigation.  It can be difficult for a veterinarian to know just by listening whether a feline heart murmur is merely a physiologic finding (i.e. there’s actually nothing wrong with the heart), or a pathologic finding (i.e. there is indeed something wrong with the heart). Physiologic murmurs are benign and can be caused by things such as stress, excitement, pain, or fever.  The only way to tell if a murmur is benign vs. pathologic is to perform echocardiography (sometimes also called a sonogram, or cardiac ultrasound).





            Echocardiography is best performed by a veterinary cardiologist. (Yes, there are veterinarians that specialize in cat and dog tickers only.) These cardiologists know exactly how thick or how thin the walls of each heart chamber is supposed to be, how fast the blood should be flowing as it travels out of the aorta and pulmonary artery, and how strongly the heart is supposed to be contracting.  By viewing the heart using ultrasound and taking a variety of measurements, the cardiologist can determine if heart disease is present.

            The most commonly diagnosed heart disease in cats is a condition called hypertrophic cardiomyopathy (HCM).  In cats suffering from HCM, the walls of the heart become progressively thicker, with one particular chamber, the left ventricle, usually becoming the most affected.  Think of the left ventricle as a coffee mug.  Now imagine the walls of the mug becoming thicker and thicker, growing inwardly.  The mug would hold less and less coffee.  In HCM, the ventricle holds less and less blood.  If the ventricle can now hold only half as much blood, the heart will try to compensate by pumping twice as hard to achieve the same effect.  Eventually, the muscle starts to give out, and congestive heart failure may develop.  Other complications, however, may arise before heart failure ever develops.  The most serious complication of HCM is a condition called aortic thromboembolism, abbreviated ATE.  In ATE, a blood clot develops in the left atrium.  A piece of the blood clot breaks free, travels down the aorta, and gets lodged at the very end, where the aorta branches to supply the legs with blood.  Cats become acutely paralyzed in the rear legs as a result.  This is a truly devastating complication that carries a very grave prognosis.  Sadly, as a feline practitioner, I have the terrible misfortune of seeing two or three cases of ATE a year, and every case ends disastrously. Sigh.  Cats diagnosed with HCM are usually prescribed a variety of medications aimed at slowing the progression of the disorder and reducing the risk of ATE, and many cats do well for many years after the diagnosis with no symptoms at all.

            HCM can strike any breed of cat, however, Maine Coons and Ragdolls are predisposed to the disorder.  Fortunately, the reason for their susceptibility was discovered several years ago: a mutation in the gene that codes for a specific protein in the heart.  A genetic test has been developed to screen cats for the disorder.  The test requires either a cheek swab or a blood sample. Responsible breeders can now test their cats for this mutation, and use selective breeding techniques to hopefully eliminate the gene from the population.

            Kittens will sometimes have a heart murmur that disappears as they mature.  A persistent murmur in a kitten, however, should be investigated, as congenital heart diseases occasionally do occur, and the sooner they are diagnosed and treated, the better the prognosis. 

           

           


Monday, January 2, 2017

Disorders of the Feline Esophagus

Disorders of the Feline Esophagus




            Last week I examined a cat that was brought to my feline-only veterinary practice for a gastrointestinal problem.  I asked the client what her main concern was, and she said that the cat was regurgitating frequently.  I asked if the cat was truly regurgitating, or if he was vomiting.  She said, “I didn’t realize there was a difference”. 

            I would venture that most people incorrectly believe that vomiting and regurgitating are synonymous.  Vomiting is the forceful expulsion of stomach contents through the mouth.  When animals vomit, the forceful contractions of the stomach are clearly visible.  Regurgitation, on the other hand, is the ejection of undigested food from the esophagus, the tube that connects the mouth and the stomach.  (In lay terms, we often call the esophagus the “food pipe”, similar to the way we call the trachea the “windpipe”.) Regurgitation is a passive process; the animal leans forward, puts its head down, and the esophageal contents are expelled.  Unlike vomiting, there is no salivation, retching, or violent abdominal contractions.  The two processes are completely different, and so are the disorders that cause them. 






            Upon further questioning of my client, it was apparent that the cat was actually vomiting, and this was no surprise.  Esophageal disorders are much less common than disorders of the stomach and intestines in cats.  Table 1 is a list of the most common esophageal disorders in cats.











            Megaesophagus is a condition in which the esophagus is weak and unable to propel food from the mouth to the stomach.  The esophagus becomes flaccid and large (hence the “mega”, derived from Greek, meaning “large”).  There are several causes of megaesophagus in the cat, such as congenital and hereditary disorders (Siamese cats are predisposed) and neuromuscular disorders (such as dysautonomia and myasthenia gravis).  In most cases, the underlying cause is never identified.  Regurgitation is the most prominent sign in cats with megaesophagus.  If megaesophagus is secondary to a neuromuscular disorder, other signs, such as weakness, muscle pain, and muscle atrophy may be present.  Some cats with megaesophagus will regurgitate food into their mouths and then accidentally inhale some food into their lungs, leading to aspiration pneumonia.  Additional clinical signs associated with aspiration pneumonia include fever, labored breathing, and coughing.   Diagnosis of megaeophagus can often be made via radiology (x-rays).  Administration of barium before the x-rays are taken greatly enhances the visualization of the esophagus, aiding in the diagnosis.  Treatment of megaesophagus consists mainly of supportive care, except in those rare cases where a treatable underlying cause has been identified.  Supportive care involves feeding frequent small meals with the cat in an upright position.  The cat is trained to eat from a bowl placed on an elevated platform.  Ideally, the cat is held upright for 10 minutes after eating so that gravity may assist the movement of food into the stomach.  Liquefied food works best. 



 
            Esophageal foreign bodies are occasionally seen in cats.  The most commonly swallowed objects are fishhooks, sewing needles, and bones.  Depending on the type of the object, the size and shape, and how long the object has been there, foreign objects can cause significant damage to the esophagus.  Clinical signs are an acute onset of gagging, retching, salivation, repeated swallowing, and regurgitation. (Table 2) Perforation of the esophagus by the foreign body is a serious complication and can cause fever, pain, coughing, labored breathing, and abscess formation. Because the likelihood of complications increases with time, identification of a foreign body should be treated as an emergency.  Most esophageal foreign bodies are visible on x-rays.  Once identified, the foreign body should be retrieved using an endoscope.  As the endoscope is passed into the esophagus and the object is seen, grasping forceps can be employed to snare it. Care must be taken to avoid creating further damage when sharp objects are removed.  If the object cannot be extracted orally, an attempt should be made to push it into the stomach, where it can be removed via abdominal surgery.   If the object cannot be removed orally or advanced into the stomach, then esophageal surgery is required.  Esophageal surgery is much more complex and expensive and has a markedly worse prognosis. 

            Gastroesophageal reflux disease (GERD) is common in people, but uncommon in cats.   It occurs when acid from the stomach refluxes, i.e. leaks backward, into the esophagus.  It is sometimes seen as a complication after anesthesia; when cats are anesthetized, the sphincter muscle between the stomach and esophagus may relax, allowing caustic gastric juice to enter the esophagus.  Conditions that cause chronic persistent vomiting, as well as anatomical conditions, such as a hiatal hernia (see next section), can also lead to acid reflux and esophageal damage. The clinical signs of GERD are similar to those of megaesophagus (Table 2).  Radiographs aren’t very helpful in the diagnosis.  The best diagnostic test is endoscopy.  The endoscope allows you to visualize the lining of the esophagus.  Affected cats will often show severe redness and inflammation, erosions, ulcers and possibly hemorrhage.  In some cases, the junction between the esophagus and stomach is seen to be wide open (in normal cats, it is closed) and reflux of gastric contents may actually be observed during endoscopy.  The goals of treatment are to prevent reflux, decrease the acidity of the stomach contents, promote healing of the damaged esophagus, and control infection.   To prevent reflux, drugs that tighten the sphincter between the esophagus and stomach and promote gastric emptying are given.  The most common are metoclopramide (Reglan) and cisapride.  To reduce gastric acid, drugs called H2-receptor blockers may be given.  Familiar ones are cimetidine (Tagamet), ranitidine (Zantac) and famotidine (Pepcid).  Famotidine is ideal for cats in that it can be given once daily.   More potent acid inhibitors, such as omeprazole (Prilosec) or pantoprazole (Protonix) may be indicated in severe cases.  Sucralfate (Carafate) is an oral drug that, if compounded as a liquid, binds selectively to erosions in the esophagus, acting as a barrier or “Band-Aid” against damage from stomach acid.  Antibiotics are usually administered to prevent or control infection by oral bacteria that may colonize the eroded areas in the esophagus.  A potential complication of foreign bodies and reflux disease is the development of a stricture (discussed below).

            The diaphragm is a muscle that separates the chest cavity from the abdomen.  There is an opening in the diaphragm, called the esophageal hiatus.  The very end of the esophagus passes through the hiatus and gives rise to the stomach, which is on the abdominal side of the diaphragm.  A hiatal hernia occurs when part of the stomach pushes through the hiatus and goes into the chest.  Sometimes the herniated piece of stomach moves back and forth through the hiatus (a “sliding” hiatal hernia); in other cases, the stomach goes through the hiatus and gets stuck there.  In most cases, it is a congenital condition, i.e. cats are born with it.  Some cats acquire the condition later in life, sometimes secondary to trauma.  Hiatal hernias cause acid reflux and many or all of the clinical signs described in the previous paragraph.  Diagnosis is usually made via radiographs, especially if the hernia is persistent (i.e. not sliding).  On the radiograph, a small portion of the stomach will be visible on the chest-side of the diaphragm.  Treatment requires surgical correction of the hernia, as well as administration of antacids and protectants.

            Esophageal stricture is an abnormal narrowing of a portion of the esophagus.  Strictures can develop after any severe injury to the esophagus, but they most commonly occur as a complication of reflux esophagitis and foreign bodies.  Certain drugs given by mouth in tablet or capsule form can result in esophageal damage and stricture if administration is not followed by a small amount of water or food, most notably the antibiotics clindamycin and doxycycline hydrocholoride.  Strictures develop slowly, so the clinical signs usually include progressively worsening inability to eat solid food, regurgitation immediately after eating, and weight loss despite an excellent appetite.  Diagnosis can usually be made via radiography after administering barium.  Barium outlines the internal portion of the esophagus and allows visualization of the stricture and assessment of the length and number of strictures present.  Endoscopy is useful for identifying strictures as well as for treatment.   Balloon dilation is a procedure in which a catheter with a deflated balloon at the tip is advanced into the stricture with the cat under anesthesia.  The balloon is then inflated, opening up the stricture.  The procedure is repeated at 5-7 day intervals.  Hemorrhage or perforation is an occasional complication.  Some cats do well, but in many cats, the stricture reforms.  In these cases, surgery may be attempted, but a guarded prognosis must be given.

            Cancer of the esophagus is rare in the cat.  The most common cancer seen is squamous cell carcinoma, usually in elderly cats.  Other tumors, such as sarcomas and plasmacytomas are seldom seen.  Because these tumors grow slowly, the clinical signs are similar to those seen in cats with esophageal strictures, i.e. slowly progressive onset of regurgitation, salivation, retching and difficulty swallowing.  Radiographs may reveal a soft tissue mass in the region of the esophagus, which is often made more visible if barium is administered before the radiograph is taken.  Endoscopy not only allows visualization of the tumor, but also allows biopsy specimens to be obtained for definitive diagnosis.  Surgical removal is the only treatment option, although the prognosis is poor, as the tumor may be too extensive to be removed. In many instances, the tumor has metastasized to other parts of the body.

            Disorders of the esophagus are uncommon in cats.  It is important that veterinarians distinguish vomiting from regurgitation in their patients. It should be re-emphasized that administration of any dry tablet or capsule to a cat should be followed by a small amount of water or food, to prevent esophageal irritation and possible stricture formation.


Table 1 – Common disorders of the esophagus in cats

Megaesophagus
Esophageal foreign bodies
Reflux esophagitis
Hiatal hernia
Esophageal stricture
Cancer of the esophagus



Table 2 – Common clinical signs of esophageal disease

Gagging
Retching
Regurgitation
Excessive salivation
Painful swallowing

Exaggerated or repeated swallowing motions
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