Diseases #23
Mast cells are most commonly seen near the surface of the animal's body. The skin and mouth are two of the common anatomical areas where mast cells live. They help build tissues and are involved in all allergic reactions in the body. Mast cells release histamine; which is the main chemical that initiates and plays havoc in animals with allergic reactions. The cause of Mast Cell Tumors is not known. The most commonly affected dog is the Boxer.
Mast cell tumors are extremely invasive. They are staged into 3 distinct types:
1. Stage 1: These mast cell tumors have a low chance of metastasis or spreading.
2. Stage 2: These mast cell tumors have a potential to be locally invasive.
3. Stage 3: These mast cell tumors are the most dangerous since they have the ability to metastasize.
The problem with Mast Cell tumors is that they can be chameleons when it comes to appearance. They can mimic many other different skin lesions. They can occur anywhere but are seen many times in the interdigital area of Boxers. They may be pigmented or non-pigmented. The masses may even be fluctuant. Signs of hepatic or splenic enlargement often suggests a metastasis to those areas. The site of the lesion may become inflamed and pruritic due to excess amount of histamine being produced by the tumor cells.
All animals should have a CBC and Chemistry profile performed to rule out (at least from a clinical pathological view) metastatic lesions in other body tissues. Ultrasound may also be used to detect liver or spleen involvement.
The most important test, prior to surgery, is the fine needle aspiration of cells from one of the tumors. In suspect animals, a proliferation of mast cells may be seen.
Diagnosis can be tentative with the detection of mast cells via a fine needle aspirate of a tumor but confirmed via histopathological diagnosis of a mass excisional biopsy to a lab. Bells and whistles should go off if the dog is a Boxer.
The majority of Mast Cell tumors are excised aggressively!! They are excised wide and deep! Care must be taken handling the tissues. Mast cell tumors can produce tremendous amounts of histamine while being excised. Many animals are treated with antihistamines prior to surgery. If lymph nodes are involved they can be excised at the same time. The key prognosticator of surgical success is the histopathological diagnosis. Even though it may show Mastocytoma as a diagnosis, the key for the animal are WIDE SURGICAL MARGINS between tumor and normal tissue. That is always good news. Animals may also undergo chemotherapy or radiation. The treatment of metastatic cases is usually not successful.
It is always a great prognosis when a mast cell diagnosis comes back with wide margins! The important thing is to always take the animal back to the veterinarian in case any other lesions may develop. It may end up being an innocuous sebaceous gland cyst but that is much more preferable than mastocytoma. Once an animal is diagnosed with the disease, ANY new growth is suspect and should be excised and sent for a pathological diagnosis. Metastatic mastocytomas have a poor long term prognosis due to the mestastasis to important visceral organs.
Megacolon is an over extension of the colon that leads to accumulation of feces and constipation. It is more commonly seen in cats and is often congenital or acquired. A common cause is loss of the nerve supply to the organ and a history of constipation that constantly distends the colon and inability hence to contract.
The colon is the part of the digestive tract that is responsible for absorption of water and sodium. Once those valuable resources have been absorbed, the other function is passage of the waste (feces) to the rectum and than outside of the body. Bouts of constipation lead to continuously dry, hard stools. The smooth muscle of the colon is stretched. Just like an incontinent urinary bladder, once continuously stretched for long periods of time, the organ stops working and feces accumulate. Clinical signs spring off of these concepts.
Clinical signs associated with megacolon are: straining to defectate, production of scanty, dry feces, passage of small amounts of mucous and blood. Once feces sit in the colon, the wastes begin to absorb water. This leads to dehydration, lethargy, vomiting and in severe cases, sepsis. It is important to make a distinction with cats. Straining of ANY type means an immediate visit to the veterinary hospital. The straining could be due to constipation or megacolon but also due to a urethral obstruction. The latter is a medical emergency! Obstipation (an obstruction to the flow of feces) can be caused by trichobezoars (hard hairballs) lodged in the descending colon.
Radiographs will show an abnormal volume of feces in a distended colon. Barium constrast studies will pick up obstructions and dilineate the stenosis of the actual lumen available for feces to pass. Ultrasounds will pick up the same thing but in greater detail. A CBC and Chemistry profile should be performed to assess organ function; particularly the white cell count. An elevated white cell count means an underlying infection, secondary to the megacolon, is starting to emerge.
Diagnosis is made by a history of constipation or obstipation over a period of time. It is much more common in cats. Radiographs, endoscopy, palpation of a hard colon from abdominal palpation are sufficient to make a diagnosis of megacolon.
Most megacolon cases are medically treated although surgery is often performed. A colectomy will remove as much of the colon that gets rid of the anatomy that was causing the problem in the first place. The big problem with this is the production of soft, frequent stools.
Medical therapy is geared to making feces easier to pass. This can be accomplished by dietary change to a food higher in roughage. Metamucil® can be added daily to the food. Lactulose may also be prescribed to loosen up stools in the colon by increased water absorption into the colon.
In severe cases, animals are extremely ill and need to be hospitalized. They are sedated and the lower bowel is manual emptied or flushed with enemas. Intravenous fluids are always given since most cats are severely dehydrated making colonic peristalsis even worse due to dehydration at the intestinal level. Antibiotics and other support care are administered.
The prognosis of megacolon is guarded at best. With either type of treatment, surgical or medical, there really is no win-win situation. The animal may feel better but the main problem is unresolved leading to recurrence of clinical signs. Many owners can not continue down that path. This eventually leads to euthanasia. Unfortunately, there is no cure for megacolon.
What I recommend is that cat owners give a small amount of a hairball preparation such as Laxatone®. This is mainly used to lubricate the gastrointestinal tract so that hair ingested by grooming can easily pass in the stool. Administering hairball prevention daily will keep stool from getting hard. Do not worry about loss of fat soluble vitamins in the stool. All hairball preparations are fortified with them. They may prevent obstipation and constipation; two of the biggest causes of acquired megacolon.
Megaesophagus is an over extension of the esophagus that leads to dilation of the organ and inability to propel, by perastalsis, food into the stomach. The causes can be either congenital or acquired. Congenital cases are seen in puppies just weaned. Acquired cases can be primary or secondary to another condition. The cause of primary megaesophagus is unknown. The most common cause of secondary megaesophagus is neurological in dogs; myasthenia gravis.
The esophagus is the tube that transfers food, after swallowing, to the stomach for digestion to commence. The organ is extremely muscular. Food is propelled by a muscular contraction known as peristalsis. What it looks like is like a snake swallowing a rodent. A person can actually watch the food pass through the snake. This is what is supposed to happen in the dog. In either cause, food becomes trapped and can not pass to the stomach. The esophagus becomes dilated and food is regurgitated up and often inhaled into the lungs causing inspiration pneumonia.
The most common sign of congenital megaesophagus in puppies is immediate regurgitation of solid food. The animal attempts to eat it over and over. Eventually it softens and it lands up in the stomach. By elevating the hind legs of the animal, one can often see the dilated esophagus through the cervical area. In acquired megaesophagus, animals will regurgitate undigested food, loose weight plus develop respiratory signs of inhalation pneumonia.
An ultrasound or barium series of the upper gastrointestinal tract will show dilitation of either the cervical or thoracic esophagus. Trapped food and or air will be seen. While examening the thoracic component, the lung fields can be studied for any signs of inspiration pneumonia.
Diagnosis is made by historical findings and clinical signs of megaesophagus. Radiographs will confirm the diagnosis with or without the presentation of inspiration pneumonia. The majority of dogs with megaesophagus are about 60-70 pounds. Miniature Schnauzers also will develop this.
This is where ladders come in handy. There is no cure for megaesophus. The best therapy for primary megaesophagus is feeding the animal a soft diet that is placed at an appropriate rung on a ladder. Elevating the food causes the animal to stand like a human so that gravity allows food to pass down to the stomach. You will have to experiment with the type and consistency of the food offered. It may be advantageous in puppies and adults to break down a meal into numerous small meals that can be passed easier than one big meal.
Acquired megaesophagus is very difficult to treat. Myasthenia gravis is an extremely debilitating disease in the dog that is diagnosed by the "Tensilon Test" (IV edrophonium chloride). Indirectly, megaesophagus may slightly improve by offering anticholinesterase drugs such as Mestinon® or Prostigman® to these patients.
The prognosis for idiopathic megaesophagus can be good if feeding instructions are followed exactly. Congenital megaesophagus has a much more guarded prognosis due to the immature anatomy in the puppy plus the constant threat of inspiration pneumonia. Secondary megaesophagus, due to myasthenia gravis, has a poor long term prognosis.
Melanoma is an extremely common cancer most commonly seen in dogs. The cause of melanoma is unknown. It is the most common cause of oral cancer in the dog and one of the most commonly diagnosed skin cancers in animals. They are extremely invasive lesions and require immediate medical care.
Most melanomas are pigmented. They are extremely invasive and metastasize rapidly to the bone and other visceral organs. Not all melanomas are pigmented. There are amelanotic melanomas that do not carry the dark pigmentation and look like any other cyst. These are often overlooked but can be just as dangerous. Humans can develop acute melanoma due to excessive UV sun exposure but this model in animals has not been proved.
Most melanomas are pigmented and found anywhere on the skin and oral cavity. They often start out as lesions that do not heal but fester and just sit there. They are often small. Melanomas on the distal (lower) extremity of a limb may cause lameness or swelling in the area. Oral melanomas will produce drooling and excessive salivation, presence of an oral mass, painful chewing and halitosis due to food particles lodged in the area of the melanoma. Metastasis is often to the liver and in some cases, a jet black urine is voided.
Radiographs and a CBC and Chemistry profile are performed to check bodily functions and pick up any metastatic lesions of the melanoma. Fine needle aspirates and or a biopsy may be obtained. Lymph node biopsies may be obtained to check for metastasis to the lymphatic system.
Diagnosis is made by the presence of lesions suspected of being a melanoma. A history of a mass that does not heal is suggestive. Diagnosis is confirmed via a fine needle aspirate or a biopsy.
Surgical treatment of oral melanomas is never satisfactory. There is no way the entire mass can be removed plus it comes back time after time again. Surgical treatment of cutaneous melanoma is made by a wide and deep excision being careful to preserve healthy margins. This is confirmed on examination of the biopsy by a pathologist. A melanoma on a toe is treated by surgically removing the toe. Radiation and chemotherapy have been also performed by veterinary oncologists.
Merial has come out with a veterinary melanoma vaccine named Oncept®. It has shown a lot of promise and is administered by oncologists.
The prognosis for dogs that do not receive medical care is poor. Their survival time is measured in months. Dogs that have been treated for oral melanoma and digit melanoma have a much greater chance for survival if Oncept® has been administered. In this instance the short term quality of life is good but survival ranges in the 1-2 year time frame.
Feline Miliary Dermatitis is a common skin condition in cats that causes excessive grooming, alopecia and pruritis (itch). The most common cause of miliary dermatitis is allergy. The most common cause of allergy in cats is to flea bites. Allergies to red plastics cause a "rodent ulcer" under the chin of the animal. Other causes can be autoimmune, parasitic or nutritional but allergy is, by far, the most common cause.
The skin in cats with miliary dermatitis is extremely sensitive. Just touching it in an exam room leads to immediate licking and grooming. I had one case, where after touching a lesion on a cats lumbar area, it literally flipped and turned circles around its own longitudinal axis! I wish I had a video of it! Cats that lick constantly will develop a secondary staph pyoderma and hairballs.
The most common clinical signs are the present of local or generalized skin lesions characterized by a scaly, pustular, inflamed raised reddish lesions over any body surface. They may also be seen under the cats chin or tail area.
A CBC and Chemistry profile are done to pinpoint an allergic condition such as a rise in the eosinophil levels. The latter are always elevated in parasitic or allergy cases. Skin scrapings are done to rule out parasites such as Cheyletiella and others. Flea combs are used to diagnose fleas or by finding the typical pepper looking flea dirt.
Diagnosis is made by the presentation of a cat with typical skin lesions associated with miliary dermatitis. An elevation in eosinophils found on lab data is helpful but doesn't tell what the actual cause is.
Treatment is geared to finding and treating the cause of the miliary dermatitis. If it is flea related, animals are put on monthly preventatives such as Revolution® and the environment is treated for fleas. If a food allergy is suspected, a food trial is recommended employing many of the available hypoallergenic diets available for animals. If rodent ulcers are the problem, use ceramic food and water bowls instead of red plastic ones. (The red dye is the suspect allergen in this case.) If a secondary staph pyoderma is present most animals will be put on Clavamox® or facsimile. Most animals are intensely pruritic and are given an appropriate dose of DepoMedrol® to control clinical signs and make the animal feel better. Hairballs are taken care of by the many hairball preparations on the market.
The prognosis for miliary dermatitis is good and depends upon the elimination or control of the offending allergen or parasite. Many animals are extremely sensitive to the bite of just one flea so flea control is mandatory. The prognosis for immune-mediated miliary dermatitis depends upon the organ involved and pathology in that organ.