2016 FALL: Deciphering Bronchial Lung Patterns | Osteoarthritis and Obesity | Heartworm Disease Update | Transfusion Related Acute Lung Injury | Meet Matthew Schmidt, DVM, DACVB
Deciphering Bronchial Patterns
Whether you are relatively new to looking at digital radiographs or not, the amount of “background” pattern in the lungs can often be misleading. The interstitium is actually visible on a normal radiograph especially in the caudodorsal lung fields on the lateral projection because of the large size of the lobes and larger amount of superimposed structures.
The interstitium appears as the lacy soft tissue opacity between airways and vessels and is more prominent in expiratory images. This opacity, however, should not blur margins of the vessels, and as long as the pulmonary vessels are distinctly visible, you can infer that lung parenchyma is adequately aerated and normal.
On top of this background opacity, the walls of the primary bronchi should be visible in a normal patient as opaque double parallel lines leaving the trachea up to the level of the second divisions. Visible bronchial walls should stay thin, linear, and distinct without blurring opacity in the immediate peribronchial parenchyma (Figure 1).
Yes, you WILL see airway walls near the hilus of the lungs in a normal dog, but you should not be able to follow these airways out into the periphery.
Figure 1. Normal canine thorax (a) in which vessel margins and background interstitium are distinctly visible. In the close-up of the hilar region (b), note only the walls of the primary bronchi are visible (white arrows).
The hallmark of a bronchial pattern is visualizing airway walls as double parallel lines (side-view, “tram tracks”) or rings (end-on-view, “doughnuts”) in the pulmonary periphery. The best places to look in the pulmonary periphery on the lateral projection are superimposed with and just cranial to the cardiac silhouette, overlying the diaphragm, and just ventral to the vertebral bodies. On the ventrodorsal projection, look lateral to the cardiac silhouette, and overlying the diaphragm caudally. Try to avoid the central hilar portions of the lung fields as these will always look “busy.” The thickening of and excess of visible airway walls in a pathologic state causes the lung fields to overall appear linear and “streaky” (Figure 2). This is a common finding in geriatric patients due to fibrosis from aging or prior disease. Bronchial patterns are typically diffuse in distribution.
One of the reasons bronchial patterns are often difficult to distinguish is that the abnormal opacity will not be as noticeable adjacent to surrounding interstitium.
Figure 2. Lateral thoracic radiograph of a 1-year-old border collie who presented for coughing, sneezing, oculonasal discharge and fever, diagnosed with infectious tracheobronchitis. Note thickened/fuzzy and prominent airway walls in the pulmonary periphery (white arrows = “tram tracks”, white circles = “doughnuts”).
However, as with many things in radiology lung patterns are not always black and white (pun intended), and mixed patterns such as bronchial and interstitial or intertial and alveolar may exist with certain disease processes. Caution must be taken to ensure an artefactual change is not to blame (i.e. underexposure or an expiratory image causing the appearance of unstructured interstitial opacity).
What does it mean?
Cellular infiltrate from primary airway disease causing wall thickening is often the cause of increased conspicuity and a bronchial pattern on radiographs, but a bronchial pattern may also result from wall mineralization, luminal exudate, thickened bronchial mucosa or peribronchial cuffing (i.e peribronchial interstitial pattern). Depending on the type and stage of the particular disease process, other pulmonary patterns may be concurrently present.
Here is a list of canine/feline differentials to consider – note some of these may be disregarded due to lack of certain endemic infectious diseases here in Texas, but travel history must be considered. Further characterization of airway disease may be obtained with airway sampling (i.e. bronchoalveolar lavage or tracheal wash) with cytology and culture, and in some cases thoracic computed tomography is helpful in better evaluating distribution and severity of disease.
Differentials for a bronchial pattern
- Allergic bronchitis – asthma
- Infectious bronchitis
- Paragonimus kellicoti (lung fluke) – dogs and cats, often with cystic lesions
- Alurostrongylus abstrusus (lungworm) – cats, often with patchy interstitial and alveolar patterns
- Heartworm – often with interstitial pattern, enlarged pulmonary arteries, and right-sided cardiomegaly
- Fungal – Histoplasmosis in cats. Other types often have pulmonary nodules and lymphadenopathy (e.g. caccidiomycosis—this occurs in neighboring states such as Arizona and California)
- Neospora caninum – dogs
- Toxoplasma gondii – cats, often with regions of patchy consolidation
- Other inflammatory bronchitis
- Toxic/inhaled irritant – i.e. smoke inhalation
- Acute lung injury/acute respiratory distress syndrome
- Cushing’s disease, hypercalcemia, hyperparathyroidism – bronchial wall mineralization mimicking a bronchial pattern
- Bronchogenic carcinoma, although often associated with mass lesions
- Pulmonary edema (an interstitial pattern that starts out as peri-bronchial with mild or early disease) – possible manifestation of cats and dogs in congestive heart failure
Article courtesy of our colleague from BluePearl in Washington, Ellie Nuth, DVM, DACVR.
Obesity and Osteoarthritis
The incidence of obesity is continuing to trend upwards, with the most recent AAHA weight management guidelines for dogs reporting that as many as 59% of our canine patients are obese. Obesity is defined as excess body fat capable of causing or exacerbating disease. When a body condition scale of 1-9 is used, each uptick in score beyond ideal is equivalent to 10-15% excess body weight.
Osteoarthritis (OA) affects at least 20% of dogs over one year of age. It can be very difficult to discuss weight management with owners; however, it is one of the most effective (and safe) treatments for OA in dogs. The take-home message for the owners of any obese dog with OA is that dogs are expected to live longer and more comfortably if they are a healthy weight. Labrador retrievers kept at a lean body weight (BCS 4-5/9) lived, on average, two years longer than their overweight littermates (BCS 6-7/9). In addition, continual pharmacologic treatment for OA is necessary in obese animals three years earlier than in those kept at a healthy weight.
Weight loss may be a daunting process for many owners. Start with small, achievable goals. Positive reinforcement is key – encourage the owners to stop by for a weight check on the clinic scale every 2-4 weeks, and make adjustments as necessary. It has been experimentally demonstrated that as little as 6% weight loss in obese animals can increase weight bearing and quality of life in dogs with osteoarthritis. Encourage moderate, controlled exercise. Gradually increasing distance of leash-walks, especially during the cooler times of day (dawn and dusk) will help maintain joint comfort and muscle mass and facilitate shedding the pounds. This time of year, swimming is also a fantastic means of exercise. Encourage owners to get into the water up to their knees to prevent their pets from running into and out of the water. Finally, professional physical therapy in conjunction with weight loss has shown more benefit than weight loss alone.
The first step to achieving weight loss is to determine exactly what is being fed. Encourage the owners to keep a journal of everything that is offered over a week’s time. Remember to keep it simple. Owners are less likely to be compliant if a “crash diet” is recommended. In addition, dogs that lose weight gradually are more likely to keep the weight off than those that quickly drop weight.
Calculate the patient’s energy requirement, and ensure that the owners are weighing the food at mealtime or using an eight-ounce measuring cup for precision and repeatability. Encourage low-calorie treats or breaking treats into multiple small pieces. Fruits and vegetables make excellent low calorie snacks (no grapes or raisins). It is important to remember that the nutrient composition of any food is calculated to provide balanced nutrition of all essential nutrients when fed based on caloric density. Therefore, if appropriate weight loss is not achievable on the diet the patient currently eats, it is recommended to switch to a weight control diet rather than substitute large volumes of food with green beans, pumpkin, etc., as deficiencies may result.
Finally, a multimodal approach to OA therapy including use of neutraceuticals, chondroprotectants, specific joint diets, NSAIDs and other analgesics is key in helping these animals be as comfortable as possible while achieving their weight loss. If an owner feels that their pet is exceedingly uncomfortable after exercise, they are unlikely to continue. When sedentary, these animals gain weight, become increasingly lame, and continue on a downward spiral.
As the Worm Turns: Current Heartworm Disease Topics
The American Heartworm Society (AHS) was founded in 1974 by a group of veterinarians and scientists with the mission of leading the veterinary profession and public in understanding heartworm disease (HWD). The AHS participates in funded heartworm (HW) research and provides easily accessible expert guidelines detailing current information on effective procedures for the diagnosis, treatment and prevention of heartworm disease. The AHS is now considered the leading expert source on HWD, a topic on which our knowledge is constantly expanding. Renewed emphasis on the importance of heartworm prevention and new information about heartworm resistance, testing and treatment prompted the AHS to revise its guidelines for dogs and cats in 2014. This article will discuss some of the topics of concern associated with the AHS guideline changes.
What about reports of heartworm resistance to the available macrocyclic lactones preventatives?
Resistance, or lack of efficacy (LOE), of a HW preventative is defined as a dog testing HW positive despite appropriate dosing and consistent monthly administration of the preventative. The majority of cases of suspected resistance to HW preventatives can be explained by owner compliance issues; either failure to administer an adequate dose or failure to administer the preventative on time. This fact has been confirmed by retrospective epidemiologic studies that evaluated dogs receiving HW preventatives with subsequent infection, including a review of the owners’ purchase pattern of the preventatives. An animal can become infected with HW by missing or delaying administration of just one dose of preventative, especially in endemic areas. If a dog on preventative therapy becomes positive for HW, it is important to question owners about appropriate administration of the preventative as well as review their preventative purchase record.
A few microfilariae strains have been identified that tolerate high doses of the macrolide preventatives. Six resistant strains have been identified with research in the past 10 years. When the L3 larvae of these microfilariae were injected into dogs they matured to adult HWs despite appropriate administration of preventative doses of the macrocyclic lactones. Resistance of these specific microfilariae strains was found with all tested products: ivermectin, milbemycin, selamectin and moxidectin injectable. The majority of resistant isolates have been identified from the Mississippi River Valley region where the majority of LOE has been reported. The extent and degree of spread of these isolates to other regions is not clearly documented. There is some concern for these isolates traveling northward, even to Canada, with the transport of rescued dogs following Hurricane Katrina. The mechanisms for microfilarial resistance are not understood and are the subject of ongoing genetic research.
Other possible reasons for LOE of HW preventative therapy include failure of attempted administration (dog spits pill out), failure of absorption of the active ingredient (GI malabsorption), biologic variation in dog’s drug metabolism, and the dog’s immune system parasite response. Failure of owner compliance remains the most consistent factor in preventative failure. The currently available preventatives are highly effective when administered per manufacturers’ recommendations with year round administration. To minimize risk of preventative failure, the veterinary practice team must educate clients regarding implications of HW infection, risk of HW in their area, and ensure that their pets are receiving appropriate preventative dosing.
What are Wolbachia and how are they involved in HWD?
Wolbachia are symbiotic gram-negative intracellular bacteria related to other rickettsial organisms. They are found in the reproductive tract of adult HW and in all stages of microfilariae. Wolbachia are necessary for all stages of dirofilariae to mature, thrive, reproduce and maintain infectivity. The pathogenesis of HWD is suspected partially related to vascular immune response to a surface protein produced by Wolbachia resulting in pulmonary and renal vasculitis. Wolbachia, like other rickettsial organisms, are susceptible to doxycycline. Use of doxycycline in conjunction with adulticide therapy is recommended to remove or reduce the number of Wolbachia from HW adults and microfilariae. Potential benefits of Wolbachia removal include reduced ability of HW adults to reproduce, reduced infectivity of microfilariae if ingested by mosquitos, inability of adults and microfilariae to thrive leading to deterioration and death, and reduction of host lung and kidney pathology by reducing reaction to Wolbachia surface protein and adult worm death. Higher dosing of doxycycline is now recommended for HWD treatment at 10 mg/kg q 12 hours for 30 days with ivermectin prior to initiation of immiticide therapy.
What about the slow-kill protocol?
Monthly treatment of dogs with preventative doses of ivermectin was found in studies to shorten life span of adult HW to two to three years instead of three to seven years. Ivermectin is the only macrocyclic lactone that has shown efficacy as an adulticide. Studies with milbemycin, selamectin and injectable moxidectin have not shown effect on adult worm survival. Subsequent studies found that doxycycline added to ivermectin therapy may shorten adult HW survival time to 9 to 24 months. These studies were the basis of the slow-kill protocol. While initially considered an alternative therapy to immiticide management, other studies have shown that dogs managed with slow-kill therapy continue to develop severe pulmonary pathology that may progress to pulmonary hypertension and heart failure. Damage to the pulmonary vasculature occurs due to pneumonitis and pulmonary vasculitis caused by the host immune response to the persistent presence of live and dying adult worms. Another concern for the slow-kill protocol is possible development of ivermectin resistance by adult HW and microfilariae that may be produced during the initial months of therapy. This could result in ivermectin resistant strains of microfilariae that may infect feeding mosquitos.
The AHS no longer recommends use of the slow-kill protocol due to risk to the patient and concern for development of ivermectin resistance. Slow-kill protocol should only be considered in patients with other significant medical illness where immiticide is contraindicated or for clients with financial hardship.
A visit to the American Heartworm Society website can provide more detail about these and other topics related to HWD.
This article was contributed by our colleague from BluePearl in Illinois, Susan E. Yohn, DVM, DACVIM, DABVP.
Transfusion Related Acute Lung Injury (TRALI): Are People and Animals the Same?
While transfusions can be lifesaving, there is always a risk of reaction as blood contains proteins that a patient can react to. Transfusion reactions occur in 8-13% of veterinary patients given red blood cell transfusions. While most of the reactions are mild and consist of a short-lasting fever, a single episode of vomiting or hives, occasional reactions can be life threatening.
In humans, the most devastating reaction is known as TRALI, transfusion related acute lung injury. With TRALI, people develop severe difficulty breathing 1-24 hours after a transfusion. With oxygen and sometimes ventilator therapy, people can survive this reaction, but it is costly and scary for the individual. This particular reaction can be confused with too much fluid that overloads the heart (TACO – transfusion associated circulatory overload) but is differentiated with an ultrasound of the heart.
TRALI occurs most commonly with plasma, not red blood cells, because the antibodies in the donor’s plasma bind to white blood cells in the lungs and cause reactions leading to fluid buildup in the lungs. Studies have revealed that these antibodies are more common in plasma from women who have had multiple pregnancies. In many places, plasma is now only used from men, and the rate of TRALI has decreased tremendously.
It is not known whether this true antibody-antigen reaction occurs in dogs or cats. But we do know that if blood is given too rapidly or in too high volume, cats and dogs can have breathing problems from the excess volume.
A recent study was published in the Journal of the American Veterinary Medical Association that attempted to answer the question of whether or not small animals suffer from TRALI.1 In this study, 54 dogs who received transfusions of either red blood cells or plasma were watched carefully for evidence of respiratory problems. All dogs had radiographs of their lungs prior to the transfusion and also had blood drawn to test their oxygenation. After the transfusion, all animals had a second blood test and second set of lung radiographs. Only two patients, or 3.7%, in the study developed a lower oxygenation level and evidence of fluid in the lungs on radiographs. Neither of those patients had signs of respiratory difficulty, so ultrasound of the heart was not performed. While these two patients might have had TRALI, it was impossible to confirm in this study. Interestingly, both of these patients had received plasma, not red blood cells. Given the increased level of antibodies in pregnant women, this low result may be explained by the fact that our donors are spayed or neutered, potentially resulting in fewer white cell antibodies in the plasma.
Until we have definitive proof to the contrary, we must assume that TRALI may be a risk for our veterinary patients and that plasma transfusions may put patients at higher risk. Any animal who has a transfusion should be observed very carefully both during and after the transfusion for any sign of reaction. Chest radiographs should be considered in any pet who develops respiratory problems after a transfusion.
Thomovsky, EJ and J Bach. Incidence of acute lung injury in dogs receiving transfusions. JAVMA. 2014; 244: 170-174.
Meet Matthew Schmidt, DVM, DABVP (Canine and Feline)
Dr. Matthew Schmidt has joined our team in Spring with 13 years of experience as a primary care clinician. He received his DVM from Texas A&M University.
Dr. Schmidt’s special interests include gastroenterology, hepatopathies, endocrine disease and calcium disorders.
Why did you become a veterinarian?
Veterinary medicine is, for me, the perfect blend of complex problem solving, compassionate service, and biological science. As a young person, I had always been drawn to medical science. Fortunately, the girl I fell in love with and eventually married was the daughter of a veterinarian. So I have her (and my father-in-law, of course) to thank for introducing me to this rewarding career.
Why did you choose a specialty and emergency hospital environment?
I always wanted to pursue advanced training in canine and feline medicine. After doing so, the transition to a specialty and emergency setting provided a unique opportunity for me to focus that training on the kinds of complex and challenging cases that I enjoy.
How do you collaborate with the primary care veterinarian?
Collaboration is built on trust and communication. I understand the value of the relationship between primary and referral veterinarian because the bulk of my career has been on the other side of the phone as the primary care veterinarian. It is important to realize that in most cases, the primary care veterinarian has invested more time, energy and relationship with the patients and clients that they have entrusted to us. Because of this, I want the primary care veterinarian to be an informed participant in the healing process.
Is there a patient that moved you?
I remember an old bloodhound named Sadie and her beloved, devoted elderly owner, Ms. Franklin, who I got to know very early in my career. Not long after we met, Sadie fell very ill. But with a series of tests and treatment and Ms. Franklin’s dedication, we were able to make Sadie feel good for several more years. Sadie and Ms. Franklin taught me, as a new vet, the value of relationship in the practice of medicine. Ms. Franklin, though she barely knew me, was gracious enough to trust me in spite of my youth and inexperience. Her trust motivated me to do everything in my ability to try to heal her sweet, old bloodhound. More importantly, the loving relationship between this person and pet was touching and probably more effective in my treatments in returning Sadie to health.
What keeps you interested day after day?
One of the best things about veterinary practice is that you never know what is going to be on the other side of the exam room door. It could be a really lovely person with a great story to tell, or an exuberantly friendly patient that knocks my glasses off, or a seriously complicated and challenging disease that needs a thoughtful solution. Every day is different. Every door is a new challenge. Every patient is uniquely rewarding.
Dr. Schmidt is not only an avid animal lover, but a devoted husband of 19 years and father of four children (3 girls, 1 boy). In his spare time, you may see him outdoors camping and hiking with his family.