Tuesday, December 20, 2016

Body Parts - The Claws

Body Parts – The Claws

            Cat feet are fascinating.  They function as shock absorbers when landing after aerial acrobatics.  The pads on the paws are thick, with a substantial amount of adipose (fat) tissue just below the pad surfaces.  This acts as a cushion, allowing for cats to walk quietly.  To me, however, the most impressive parts of the feet are the claws. 

            All members of the family Felidae have claws.  The claws are retractable.  When the foot is relaxed, the claws remain sheathed by a layer of modified skin, which is surrounded by the fur on the toes.  Keeping the claws sheathed helps prevent wear and tear by minimizing contact with the ground.  When necessary, cats can voluntarily extend the claws on one or more paws.  The most common reasons for exposing their claws are hunting, self-defense (often against veterinarians, unfortunately), climbing, “kneading”, and for extra traction, like when my new kitten dashes across our expensive Persian rug.

            Cats typically have five toes on their front paws and four toes on their back paws, and each of these toes has a claw associated with it.   Not all cats conform to the formula of five toes in the front and four in the back, however.  A naturally occurring genetic mutation occasionally occurs, causing cats to have extra toes.  This is called polydactylism.  My adult cat, Mittens, is polydactyl, hence her corny name.  As you can see in the photo, it’s an appropriate moniker.  Her feet are huge! 

            I see a fair number of claw injuries in my feline-only veterinary practice.  The most common are broken nails and overgrown nails.  Broken nails often occur because the claw becomes entangled in a carpet or thick fabric.  When the cat pulls the foot loose, the nail can tear.  Sometimes, the nail gets completely torn off. In most cases, the nail is only partially torn off and is dangling, causing pain or discomfort every time the nail touches anything.  Torn nails are uncomfortable for the cat because after a tear, the underlying tissue, called the quick, becomes exposed.  The quick contains blood vessels and nerve endings and is sensitive.  A torn nail often causes the cat to limp on the affected foot.  In severe cases, the cat may refuse to bear any weight at all on the foot.  Treatment for a partially torn nail involves removal of the dangling piece of nail by your veterinarian.  Because cats scratch around in their dirty litter boxes with their feet, the exposed quick is at risk of becoming infected.  Your veterinarian may prescribe antibiotics and possibly pain medication.  A new nail often regrows from the exposed quick, however, that nail may end up looking malformed compared to the others.

            If a cat’s claws aren’t trimmed regularly, the claw can grow long enough that it actually curves all the way around and can pierce the pad of the affected toe.  The wound that occurs may get infected, causing pain and discomfort to the cat.  Treatment requires trimming the offending claw.  This should be performed by your veterinarian and should not be attempted at home.  If the pad is infected, your vet will prescribe antibiotics.  In some cases, soaking the foot in an antiseptic solution may be beneficial.  Overgrown nails seem to happen only in the front feet.  The rear nails are shaped differently.  Rear claws may grow very long if untrimmed, but they grow outwardly rather than curving down and around.  

Overgrown claws can be prevented by keeping your cat’s nails trimmed.  Arden Moore, in her book “Fit Cat”, gives a few quick and easy steps for giving your cat a “pet-icure”:

·      Get the equipment you need: nail clippers designed specifically for cats, a thick towel, and styptic powder (in case you trim a nail too short and it bleeds)

·      Wrap your cat in a large bath towel, exposing one foot at a time.

·      Position your thumb so that it rests on top of one paw, with your fingers of that hand underneath.  Gently press on the top of one of the toes to expose the nail.

·      Snip the clear, white tip of the nail.  Do not cut too close to the pink part (the quick), or you might nick the vein that runs through the nail, causing bleeding.

·      If you do nick the quick, apply a little styptic powder to stop the bleeding.  If you don’t have styptic powder, direct pressure on the nail with a tissue or paper towel will stop the bleeding quickly.

·      Give lots of praise to your cat during the nail trimming session, so that your cat might see it as a positive experience.

            To make nail trimming less stressful for your cat, start them young.  Play with your kitten’s feet regularly to get them used to being handled.  Gently squeeze the footpads to expose the nails, and then release.  Give a healthy treat after handling the feet.  Cats who have had their feet handled frequently as kittens are more amenable to nail trimming.  Some cats, however, simply will not allow their owner to trim the nails.  In these cases, taking the cat to your veterinarian or to a groomer should solve the problem.   Claws should be trimmed approximately every six to eight weeks.


Monday, December 19, 2016

The Feline Adrenal Glands

Body Parts – the Adrenal Glands

            I would venture that most people have heard of the adrenal glands.  I would also bet that if asked about what the adrenals do, most folks would correctly guess that they make adrenaline, the "fight or flight" hormone that makes your heart race before that first big plunge on the roller coaster.   But the adrenals do so much more than just make adrenaline.  These small glands are impressive little hormone factories, producing substances that control electrolytes, influence blood pressure, manage stress, and help regulate blood sugar.

            The adrenals, as their name implies (from the Greek: ad = on top of, renal = kidney) are located just above each kidney.  The gland is comprised of two parts, the outer portion, called the cortex, and the inner portion, the medulla. 

            The cortex can be subdivided even further, into three layers.  Each later produces different hormones.  The outermost layer produces aldosterone, a hormone that controls blood pressure by adjusting the level of sodium and potassium in the body.  The middle layer produces cortisol, a steroid hormone that regulates metabolism and helps the body manage physiologic stress.  The inner layer produces sex hormones such as estrogen and progesterone, (although the majority of the sex hormones come from the ovaries and testes.)
            The medulla is where adrenaline (also known as epinephrine) is manufactured by the body.   As mentioned above, this hormone helps the body spring into action in an emergency by increasing heart output and blood pressure, and raising the blood sugar.

            Fortunately, cats are much less susceptible to adrenal disorders compared to dogs.   Many veterinarians forget to even put adrenal disorders on their list of possibilities when dealing with cats, causing these ailments to be underdiagnosed in cats.  The three most common of these uncommon conditions are Cushing’s disease, Addison’s disease, and Conn’s disease.

            Cushing’s disease (the proper name is hyperadrenocorticism) is a condition in which the adrenal gland is producing too much cortisol.   There are two main reasons for this: either the pituitary gland is telling the adrenals to make more cortisol than it should, or there’s a tumor of the adrenal gland that is producing cortisol uncontrollably.  In cats, the pituitary is the culprit 80% of the time.  Cortisol-secreting adrenal tumors in cats are very rare.    The main signs of feline Cushing’s disease are excessive thirst and urination, weight loss despite a voracious appetite, a pot-bellied appearance, hair loss, and thin papery skin.  Diagnosis is made by special blood tests and imaging techniques like ultrasound or CT scanning.  There are medications that can be given to control cortisol secretion from the adrenals, however, if an adrenal tumor is the cause of the condition, surgical removal of the tumor might offer the best chance of treatment.

            Addison’s disease (hypoadrenocorticism) is basically the opposite of Cushing’s disease.  In this condition, the adrenal gland is making an inadequate amount of hormones.   In most cases, the adrenal produces insufficient aldosterone and insufficient cortisol.  In some cases, however, the adrenal produces inadequate cortisol only.  This is known as “atypical” Addison’s disease.   Clinical signs of the disorder are non-specific and include poor appetite, lethargy, weakness, vomiting, and diarrhea. Routine bloodwork may suggest the presence of Addison’s disease, however, a special blood test, called an ACTH stimulation test, is necessary for a definitive diagnosis.  Treatment requires administration of the deficient hormones.

            Conn’s disease (hyperaldosteronism) is an adrenal disorder in which the adrenal cortex produces excessive amounts of the hormone aldosterone. It is the most common adrenal disorder in cats.  [Note: the other two feline adrenal disorders are commonly referred to by their eponyms, Cushing’s and Addison’s.  For some reason though, hyperaldosteronism is rarely called Conn’s disease in veterinary medicine. Convention, I suspect.]   Excessive aldosterone will cause the blood sodium level to rise and the potassium level to drop.  This can lead to dangerously high blood pressure as well as severe muscle weakness.  The most common cause is a tumor of the adrenal gland.  In cats, about half of these tumors are benign, and half are malignant.  Routine blood tests may be suggestive of hyperaldosteronism, but a definitive diagnosis often requires measurement of aldosterone levels in the bloodstream as well as some form of diagnostic imaging, such as ultrasound or a CT scan, to better assess the adrenals.   Treatment can be either medical or surgical.  Surgical removal of the adrenal tumor can potentially cure the condition, however, surgery isn’t always an option either due to cost, anesthetic risk to the cat, or invasion of the tumor into the vena cava (a major blood vessel) making surgery too dangerous.  For cats that are poor candidates for surgery, medical management is recommended.  This involves controlling the blood pressure with a drug called amlodipine, administering another drug called spironolactone which counteracts the effects of the aldosterone, and supplementing the diet with extra potassium, so as to maintain a normal blood potassium level.  The dosages of these drugs may need to be increased as the disease progresses over time.  If the tumor has not spread and it can be completely removed, the prognosis is excellent.  Cats undergoing medical management may do well for many months or even years, as long as they receive their medication and are monitored closely.

Thursday, December 8, 2016

Lymph node enlargement in the cat.

Lymph Node Enlargement in the Cat

We’ve all heard of lymph nodes, but what exactly are they?  What do they do?  And why be concerned when they become enlarged?

            As a feline veterinarian, I perform dozens of physical examinations every week.  Every veterinarian performs the physical exam in his or her own style, making sure to evaluate all body systems thoroughly.  Assessment of the lymph nodes is unquestionably a part of every veterinarian’s physical exam. 

            The lymphatic system is an arm of the immune system that plays a role in the development of the body’s immune response. Lymph is the fluid that flows through the lymphatic system.  It is rich in protein and white blood cells.   Cells of the immune system circulate throughout the lymphatic vessels in the body. Lymph nodes are small, oval-shaped organs that make up part of the lymphatic system.  As lymph flows through the lymphatic vessels, it passes through at least one set of lymph nodes, and often several sets, before ultimately emptying into the general circulation where it mixes with blood.   The lymph nodes are the major sites in the lymphatic system where the immune cells gather.   

            Lymph nodes have a distinct anatomical structure, consisting of an outer portion called the cortex, and an inner portion called the medulla.  The cortex contains large numbers of lymphocytes, often arranged in clusters (follicles). There are two distinct types of lymphocytes found in lymph nodes: T lymphocytes and B lymphocytes. The B lymphocytes are responsible for producing antibodies, a process called “humoral immunity”.  T lymphocytes, once stimulated, are involved in a process called “cellular immunity”, the details of which are probably beyond the scope of this discussion.  The medulla contains lymphocytes as well as many other cells of the immune system, including macrophages and dendritic cells.  The entire lymph node is surrounded by a capsule comprised of connective tissue. 

            The immune system’s job is to protect and defend the body against harm by mounting an attack against invading substances (antigens).  When an antigen invades the body and makes its way to the lymphatic system and eventually to the lymph node, it stimulates a discrete population of lymphocytes in the node. This causes those lymphocytes to proliferate and transform, or become “activated”.  As noted above, activated lymphocytes may produce antibodies that neutralize the antigen, or the lymphocytes may become involved in more complex “cellular” immune responses.  When these lymphocytes proliferate, lymphadenopathy develops. Lymphadenopathy is the medical term for an increase in lymph node size.   Stimulation of the immune system is a common cause of lymph node enlargement.  Cancer is an equally common cause.

            Lymphadenopathy is sometimes noted as an incidental finding during physical examination of the cat.  Occasionally a cat owner will bring a cat to the veterinarian because of clinical signs related to the lymph node enlargement, for example, difficulty swallowing due to enlarged retropharyngeal lymph nodes (located at the back of the throat.  See sidebar.)  Sometimes a cat owner will bring a cat to the veterinarian because they’ve detected a lump, which turns out to be an enlarged lymph node, while patting or stroking the cat. 

            The age of the cat is important when considering the significance of lymph node enlargement.  Kittens and young cats are exposed to a variety of antigens early in their lives, and an increase in lymph node size is an expected response by the immune system.  As cats mature, lymph node size usually decreases and the nodes often become more difficult to palpate in older animals.  However, in geriatric cats or cats that have lost weight due to illness, the loss of body fat around the lymph nodes may make the lymph nodes appear more prominent than expected.

            Cancer, unfortunately, is a common reason for lymph node enlargement.  The size and texture of the lymph node may give clues in this regard.  Enlarged, firm, painless lymph nodes that are freely moveable is usually associated with primary lymph node cancer, i.e. lymphoma.  Very hard lymph nodes are more suggestive of metastatic cancer, i.e. a cancer arising in another site in the body that has spread to that lymph node.   The degree of enlargement may offer some clues as to the cause. Marked lymphadenopathy (the lymph node is 5 to 10 times the normal size) most often occurs with a lymph node abscess or with lymphoma; metastatic cancer rarely causes lymph node enlargement of this magnitude. 

            The location of the lymph node enlargement should also be considered in the patient evaluation.  If one lymph node is enlarged, or one regional group of lymph nodes is enlarged, one should carefully evaluate that area of the body for evidence of inflammation, infection, or cancer.  For example, if the right submandibular lymph node (the node just below the jaw) is enlarged, the right side of the mouth should be examined carefully.  A tooth root abscess involving a tooth on the right side, for example, could cause this nearby lymph node to be enlarged.   If, however, all of the lymph nodes involving the head region are enlarged, a more diffuse illness involving the head, such as an upper respiratory infection, would be something to consider.

            Obtaining a diagnosis in cases of lymph node enlargement may require a variety of tests, including blood and urine analysis, x-rays, and ultrasound.  Ultimately, a definitive diagnosis often requires obtaining a sample of cells from the node itself.  This is usually achieved either by aspiration cytology, or by surgical biopsy.

            Aspiration cytology is a procedure in which a needle, attached to a syringe, is inserted into the lymph node.  Suction is applied to the syringe so that cells from the lymph node are aspirated or sucked into the hub of the needle.  The contents are then sprayed onto a microscope slide and are sent to the laboratory for interpretation.  The advantage of this procedure is that it fairly non-invasive and inexpensive.  A disadvantage is that the aspirate may not yield enough cells to make a diagnosis.  Only positive findings are diagnostically useful.  The absence of abnormal findings in an enlarged lymph node means that the diagnosis is still unresolved. 

            Biopsy of the lymph node is the definitive diagnostic test in evaluating lymph node enlargement.  Depending on the size and location of the node, either the entire node is removed (this is called “excisional biopsy”), or a small piece of the lymph node is removed (this is “incisional biopsy”).  The biopsy specimen is then evaluated by a pathologist.  Treatment is based on the biopsy results: infections are usually treated with antimicrobials; cancer is treated by chemotherapy, surgery, radiation, or a combination of these.

            Lymph nodes are encapsulated structures containing aggregates of cells of the immune system that are capable of responding to a wide variety of invading antigens.  Enlargement of the lymph nodes occurs either due to reactive enlargement (stimulation of the immune system), primary cancer of the lymph nodes (lymphoma), or metastatic cancer.  Infectious causes of lymph node enlargement are more common in younger animals, while cancerous causes tend to be seen in older animals, although there is considerable overlap.  The size, location, and texture of the enlarged node(s) may offer clues as to the cause, and diagnostic tests such as x-rays, ultrasound, and blood and urine tests give valuable diagnostic information, however, obtaining a sample of the enlarged node is usually required for a definitive diagnosis to be achieved.

Sidebar: names and locations of some of the feline lymph nodes

Submandibular – just below the mandible (lower jaw)
Retropharyngeal – in the back of the throat
Cervical – in the neck, along the trachea
Axillary – in the armpit
Sternal – inside the chest along the sternum (breastbone)
Tracheobronchial – associated with the bronchi (airways) in the lungs
Sublumbar – above the colon, just below the spine
Inguinal – in the groin area
Popliteal – along the back of the thigh
Epigastric – adjacent to the stomach
Mesenteric – in the abdomen, associated with the intestines

Inflammation and enlargement of the lymph nodes is a common finding in companion animals.  Infection is a common cause of lymph node enlargement.  Cancer is also a common reason for lymph node enlargement.
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