Diseases #22
Pneumothorax is the presence of air in the thoracic cavity. Atelectasis is when a lobe or part of the lung becomes airless and collapses on it own. This presentation will be on lung collapse due to pneumothorax. The most common cause of lung collapse in animals is blunt trauma to the chest. The pneumothorax may be caused by a fractured rib that punctures the thorax or a knife or other penetrating weapon that pentetrates the thorax. It may also be caused by primary or secondary lung disease. It may be open or closed. A penetrating wound into the thorax is open; meaning a direct opening from outside to inside. Lung disease produces a closed pneumothorax
Air pressure always goes from a high pressure environment to a low pressure environment. The thoracic cavity of mammals is under a NEGATIVE pressure environment while the air we breathe is under a POSITIVE pressure environment. If the thoracic cavity is exposed to the outside environment, high pressure goes to low (negative) pressure and the lungs collapse due to the pressure gradient. This explains the clinical signs and therapy that is provided.
The most obvious clinical sign is difficulty breathing (dyspnea). Because the lungs are collapsed, it is difficult bringing air into the lungs and breathing is always shallow and rapid. In most cases the left or right lung is involved unless there has been severe trauma to both sides of the thorax. With difficulty getting air into the lungs the animal may be cyanotic with its tongue and mucosal membranes turning a shade of blue. Dogs and cats will also sit upright making it easier to breathe.
Radiographs are always performed with pneumothorax. They will show the characteristic heart elevation. The base of the heart is normally anatomically close to the sternum (breast bone). In the case of pneumothorax, it may be an inch or two elevated!
Diagnosis is made by the presentation of a dog in dyspnea with traumatic wounds or lesions to the chest wall. Radiographs confirm the diagnosis.
The main goal of treatment is the correction of the trauma to the chest wall and recreating a negative chest pressure. The latter is accomplished by thoracocentesis. A large syringe is hooked to a stopcock and air is continually sucked out from the chest. Eventually difficulty doing this means the chest wall is becoming negative. This is repeated as necessary and the animal is confined for weeks with no exercise. Any tissue damage is repaired and the dog or cat is put on antibiotics. The animal is usually radiographed in a day or so to check the progress of the pneumothorax.
The prognosis for most pneumothorax corrections is very good as long as treatment is immediately sought and there is no severe crushing trauma to the pulmonary and heart vessels. Those cases have a poor prognosis.
The cause of lung tumors in dogs and cats is unknown. The most commonly seen lung tumor in the dog is an adenocarcinoma. This tumor is extremely malignant and metastasizes to other tissues such as the brain, liver and lymph nodes.
Lung tumors are very difficult to deal with. Since a cause is not known, it is very difficult to visualize them as they start. They are composed of cells that have undergone a harmful mitotic change. These cells and eventual tumor development are often diagnosed when the tumor is well established. This means when the tumor becomes calcified and visible on chest films. By that time, cancer cells have spread through the circulatory and lymphatic ducts. The lymphatic system is usually affected due to the proximity of the lungs to the lympatic thoracic duct.
Clinical signs are always respiratory related unless signs of other organ systems have developed due to metastasis. Dogs are seen with this condition more so than cats. Cases are most commonly seen in older dogs. Primary pulmonary neoplasia is less common than pulmonary lesions that have developed secondary to cancers elsewhere in the body. An example of this are mammary masses. Difficulty breathing and vomiting of blood are commonly seen. Lack of appetite, poor coat and associated weight loss are the most common respiratory signs. Lymphatic involvement will usually be associated with peripheral lymph node enlargement. Liver disease will show elevated liver enzymes and others such as jaundice.
If lung tumors are suspected radiographs are the first order of business as they may show calcified lesions. A CBC and Chemistry profile are performed to assess whether other organ systems have been affected by metastasis of the primary tumor. Animals may also have an ultrasound performed.
Diagnosis of lung tumors is made by the history and results of a physical exam. Many times an ultrasound and radiograph will show characteristic calcified lesions.
Lung Cancer patients are referred to a veterinary oncologist. Treatment protocols vary with the individual, severity of the primary disease and other organ systems affected. Surgical care may involve removing a lung lesion or lung lobe. To increase survival, radiation and chemotherapy may be offered.
The prognosis for lung tumors is poor. With metastasis of the tumor, most dogs will not live longer than a year. Even with treatment, survival is really not extended much at all. Owners need to be made aware of the very likely possibility that the animal's quality of life will decline over time.
Lyme disease is a common world wide disease seen in humans and their companion animals. Lyme disease is named for Lyme, CT where the disease first was discovered. It is caused by the bacterial spirochete, Borrelia burgdorferi. In animals it causes a severe lameness due to joint inflammation.
Transmission of Lyme disease is by the bite of the larval form of the deer tick. Since the larval form is so difficult to see, most owners do not see the tick on the animal. After a day, the insect falls off and is gone. The disease in the United States is commonly diagnosed in New England and the Mid-Atlantic states. It is also seen in the Ohio Valley and Upper Midwest. In fact, most veterinarians in the northeast will screen ANY dog that comes in limping for Lyme disease.
The most common clinical sign noticed is lameness in any limb or combination of limbs! This is known as polyarthritis. The dog may be treated with an antibiotic and lameness shows up in another limb. It may disappear in a few days and a different joint is affected! Sort of like whack a mole. Later on in the disease acute renal failure, due to glomerulonephritis, may demonstrate itself as increased fluid and urination and associated halotosis. The central nervous system may be involved. Seizures or fascicular tics may be noticed.
A CBC and Chemistry profile should always be done on suspect Lyme disease patients. Involvement of other organs such as renal failure can be figured out via a profile. There are specific tests to pick up the spirochete. An antibody test can be performed that picks up antibodies to the spirochete. If this is positive it is a sure thing. If it is negative, the dog may still have the disease. Not enough time may have passed for the immune system to produce antibodies, the animal is immuno-suppressed or the animal has had the infection for eons with very little circulating antibody around anymore. A PCR (Polymerase Chain Reaction) test can truly identify the organism but it is not always around in the blood. To run this test, fluid is usually tapped from the affected joint.
A tentative diagnosis of lyme disease can be made by the presentation of an animal with a fever, swollen joints and lameness. A history of exposure to deer ticks in the environment is important. In some areas, there are more deer around than people! A diagnosis may be confirmed via a PCR or antibody test.
The primary treatment of Lyme disease is by antibiotics. One of the commonly used drugs is Doxycycline. Antibiotic therapy should last for at least 4-8 weeks. Sometimes clinical signs will reappear and other antibiotics may need to be used. Even when the disease is treated, the lameness may persist if there has been mechanical damage to the joint. Renal disease must also be treated. Glomerulonephritis caused by the Lyme circulating antigen/antibody complexes can be treated with fluids and oral benazepril.
The prognosis for treating Lyme disease successfully is very good but the animal can get bit by an infected tick at any time in the future. This will set up another infection. In this case, will a humoral antibody response to a prior infection protect a dog? Maybe.
The key is to prevent the animal from coming into contact with ticks in the first place. By removing the tick with tweezers and twisting counter clockwise will usually remove the head parts also. The big problem is that the larval deer tick is very small and naked to the eye. Best approach is to use one of the topical flea/tick preparations such as Frontline® Plus, a Preventic® or Seresto® collar. Environmental control of tick populations can be controlled in the home with sprays or foggers. Outdoor environmental control may be done with chemicals but the best approach is to cut down tall grasses and weeds. This is where most tick populations will reside.
There is a vaccine for Lyme disease available. It needs to be administered once and than again in about 3 weeks. It is than boostered annually. Talk to your veterinarian about the use of the vaccine in your area of the country.
Lymphomas are not that common in dogs. They involve neoplasms or cancers of the lymphatic system. The lymphatic system is crucial for humoral defenses plus the elimination of organisms as they are filtered through that system. The actual cause of the mitotic cellular changes that cause lymphoma is unknown.
Lymphocytes are just one type of white cell found in the blood of mammals. Their main function is involvement in the immune system of the animal. There are two types of lymphocytes; B-cell and T-cell. The B-cell lymphoma is more common in dogs and causes pathology in the lymph nodes, bone marrow and visceral organs.
The development of clinical signs depends upon the location of the lymphoma. If localized in the lymph nodes, peripheral lymph nodes may be enlarged. If in the digestive system, signs of diarrhea and associated weight loss may be seen. If in the liver, weight loss plus increased thirst and urination plus jaundice may be seen. General signs of weakness and anorexia may also be seen.
If lymphoma is suspected, a complete workup is in order. This means a CBC and Chemistry Profile to check for organ involvement. A CBC may show an anemia or a drop in platelets or other disorders due to bone marrow involvement. A urinalysis will be performed and radiographs or an ultrasound will be added to the list. If a lymph node is enlarged, a biopsy and histopathologic diagnosis will be obtained.
A tentative diagnosis of lymphoma may be made by the presence of a larger breed dog with associated lymph node enlargement. Other clinical presentations will be more difficult to diagnose. A diagnosis may be confirmed by a fine needle aspirate or biopsy of an enlarged lymph node. Biopsies may also be taken during an abdominal exploratory.
There is no cure or specific treatment of lymphoma in the dog. They may be referred to a veterinary oncologist where radiation or chemotherapy may be done. The COP (Cytoxin®, Oncovin®, Prednisolone) protocol also has been used along with other chemical approaches.
The long term prognosis for Canine Lymphoma is not good. The most important goal is to control the disease process as best as possible and to insure the best quality of life as possible. Everything should be done to make the animal's life as fullfilling and comfortable as possible. Lots of kisses and a lot of TLC will go a long way. Including this veterinarian, it is a horrible disease to see an animal go through.
Lipomas are soft benign tissue that are commonly seen under the skin in animals as they age. The cause of lipomas is unknown but it seems to be more predisposed to in obese animals.
Lipomas can form anywhere on the body. They are usually about an inch in diameter but some can become massive to affect the animals mobility. In most cases they do not bother the animal but should be attended to. There are liposarcomas that are malignant and can metastasize to internal organs. However, the benign version is much more common in companion animals..
The most common finding is a fluctuant, soft mass over the skin but not normally attached to the subcutaneous tissue. This occurs most commonly in middle aged animals.
Most animals are healthy. Often a fine needle aspirate may be done to stain and visualize characteristic fat cells.
Diagnosis is made by the presence of a soft, golf ball sized, fluctuant mass anywhere on the animal's body. They are seen most often on the trunk, ventrum and posterior areas. A biopsy can confirm the diagnosis.
Treatment is always surgical. An incision is made directly over the lipoma and they pop out looking like oysters! Dead space is closed and the wound is sutured shut with non-absorbable sutures. The mass is than sent out for histopathological diagnosis. It is important to get a pathological diagnosis so as to not overlook a liposarcoma.
The prognosis for lipomas are excellent. More may pop up on the animal's body as it ages. The more infiltrative liposarcomas can be more invasive and a guarded prognosis is often given.