Siberian Huskies Are Among Breeds Overrepresented in Pneumothorax Cases
It was the middle of the night when Denise Bouchard, of Turners Falls, Mass., was awakened. Her 6-year-old female Siberian Husky, "Blanqua," was lying beside her, breathing heavily. By morning, the dog still struggled to breathe, her sides heaving with each breath. Bouchard rushed Blanqua to the veterinarian.
A radiograph indicated Blanqua suffered from a mass in her chest or a collapsed lung. Bouchard was referred to the local emergency hospital, where specialists performed a thoracocentesis, or chest tap, to relieve pressure on Blanqua's lungs. The pressure was caused by pneumothorax, a disorder where air escapes from the lungs and seeps into the chest cavity.
When a dog suffers from pneumothorax, air from the lungs is trapped in the pleural space surrounding the lungs, which causes one or both lungs to collapse. Traumatic pneumothora, the most common type, is caused by an injury to the chest that ruptures part of a lung. Spontaneous pneumothorax may be idiopathic or caused by tumors, foreign bodies or infection. Idiopathic cases occur more commonly in large, deep-chested dogs. Siberian Huskies are among the high-risk breeds for spontaneous pneumothorax.
"My last two cases of pneumothorax were Siberian Huskies," says MaryAnn Radlinsky, D.V.M., DACVS, associate professor of soft tissue surgery at the University of Georgia College of Veterinary Medicine in Athens. "When I get a Husky with pneumothorax, often both lungs are involved."
In spontaneous pneumothorax, small air-filled blister-like sacs called blebs or bullae may form on the surface of the lungs. Blebs are less than 1 centimeter in diameter and typically form under the visceral pleura. Bullae are larger and form in the parenchyma of the lung. Siberian Huskies typically develop bullae that cause their pneumothorax.
"A problem occurs if one or more blebs or bullae burst," says Sheila Morrissey, D.V.M., of Greenfield, Mass, Blanqua's primary-care veterinarian and the Siberian Husky Club of America genetics chair. "This releases air from the lung into the pleural space." Normally, the lungs expand when inhaling due to negative air pressure created when the chest expands. The diaphragm and chest wall expand, creating a vacuum that pulls air into the lungs. When air is filling the pleural space, it prevents the lungs from expanding with the diaphragm and chest. The more air that fills the pleural space, the less air fills the lungs and the more difficult it becomes for a dog to breathe.
Both lungs are affected when the air in the pleural space diffuses across the thin wall separating the two halves of the chest. In the worst cases, known as tension pneumothorax, the opening from the lung acts like a one-way valve releasing air into the pleural space every time a dog inhales, trapping air in the pleural space. The pleural space has no outlet for the air, and the pressure increases until it's higher than the atmospheric pressure. When this happens, the lung collapses severely. Blood vessels also may collapse, which could cause a dog to go into shock and die.
Depending on how much air and how rapidly it fills the pleural space, dogs may show nonspecific signs a few days before it becomes obvious something is wrong. Signs include rapid breathing, loss of appetite, coughing and vomiting. Less common signs are lethargy, fever, gagging and exercise intolerance.
Most owners notice that something's wrong when a dog starts breathing rapidly while trying to get oxygen. The dog may become anxious and restless and refuse to lie down because it's harder for the chest to expand in a prone position, especially when lying on the side. The mucous membranes in the mouth may be pale or bluish, the heartbeat may be faster than normal, and the femoral pulse may be weak.
A veterinarian will check for these signs as well as use a stethoscope to listen for the characteristic muffled heart and decreased breathing sounds. The next step depends on the severity of the signs. If a dog is stable, radiographs may be taken to determine if air is in the pleural space, to estimate the extent of the problem, and to check for tumors or parasites, such as heartworms.
If a dog is not stable and signs indicate pneumothorax, the veterinarian may skip imaging diagnostics and perform a thoracocentesis. In this procedure, a needle or catheter is inserted between the ribs into the pleural space to remove trapped air until the lung has room to expand normally. Ideally, a dog receives supplemental oxygen throughout the procedure. A dog should be monitored in a 24-hour veterinary hospital after air is removed because of the risk of a potentially fatal air leak due to tension pneumothorax.
While a thoracocentesis procedure is an efficient and effective first step, it's not a panacea for stabilizing a dog. "Thoracocentesis alone probably won't take care of most cases of spontaneous pneumothorax," says Radlinsky, whose patients often are referred after a thoracocentesis has failed to alleviate the problem. "We usually place a thoracostomy tube in a dog and begin continuous controlled suction." A thoracostomy tube is a flexible tube inserted through the dog's rib cage into the pleural space to continuously remove air.
"We monitor the dog with a thoracostomy tube in place for two to four days," Radlinsky continues. "We hope that during this time the place where air is leaking will seal. When we send a dog home, it is under strict confinement — no running or barking and mandatory quiet behavior is required for two to four weeks. Any change in pressure in the chest could break the seal."
Although traumatic pneumothorax usually responds well to conservative treatments, such as a thoracocentesis or tube thoracostomy, spontaneous cases tend to respond poorly and have a higher recurrence rate. "If it's truly spontaneous pneumothorax, surgery usually is the best option," Radlinsky says. "When the patient is a Siberian Husky, I know from experience that surgery almost certainly will be needed."
Surgical Options for a Collapsed Lung
Surgery for pneumothorax traditionally entails splitting the sternum and spreading the rib cage to expose the chest cavity, a procedure similar to open-heart surgery in humans. A dog is fairly comfortable in about a week but must remain quiet for one to two weeks. "As with any bone, the sternum takes a while to heal," Radlinksy says.
During surgery, blebs or bullae are removed and sometimes entire lobes of the lung must be removed. Radlinsky uses a computed tomography (CT) scan to help detect abnormal lung tissue. Although a CT scan can cost more than $1,000, Radlinsky notes that having a scan helps to ensure the removal of abnormal tissue during surgery.
"Before CT scans, we would fill the chest cavity with saline and look for bubbles," Radlinksy says. "Even with a CT scan, the lung tissue has to be inspected for blebs or bullae. I also remove deflated areas of the lung and any tissue that looks abnormal. No more than 50 percent of both lungs can be removed, or a dog could die."
Radlinsky prefers using a minimally invasive surgical technique in which a thorascope is used to guide instruments inserted into the chest through small portals. "We still do basically the same thing as during traditional surgery once inside," she says. "We examine the entire lung and use saline to look for leaks. The main difficulty is that we can't maximally inflate the lungs because the chest is closed or they will press against the chest wall. We always are concerned that we may not inflate the lungs enough to show a leakage. That's why it's especially important to have a CT scan."
If necessary, the procedure can be aborted for traditional surgery that is performed at the same time. Alternatively, part of a lung can be removed through an incision made in a dog's side between the ribs, which causes less pain than spreading the rib cage.
Benefits of thorascopic surgery are less postsurgical pain and a quicker recovery. Not enough minimally invasive surgeries have been performed to compare them to traditional surgery.
In Blanqua's case, she was transferred to the Cummings School of Veterinary Medicine at Tufts University in North Grafton, Mass., for traditional surgery. A surgeon removed 40 percent of one of Blanqua's lungs due to blebs. Recovery was slow, and she was hospitalized almost 10 days. "It took about two to two and half months for her to be back to her old self," recalls Bouchard. "The only issue afterward was that she went on shorter walks than before — 10 to 15 minutes and she's done."
Without surgery, dogs that have spontaneous pneumothorax are almost guaranteed a recurrence. With surgery, the recurrence rate can be up to 25 percent. Although surgery is initially more expensive, considering the cost of repeated or prolonged hospitalizations, it is often less expensive in the long run.
Blanqua's surgical bill was about $7,000, a fee that Bouchard says she would pay again if it meant saving her beloved Husky. Now 12 years old, Blanqua has gone almost six years without a hint of a recurring episode. As Bouchard says, "You'd never know she had the surgery."
Banking DNA for Answers
Since pneumothorax could be an inherited condition in Siberian Huskies, future research may focus on identifying the causative gene. In the meantime, Bouchard sent a blood sample from Blanqua to be banked at the Canine Health Information Center DNA bank (www.caninehealthinfo.org/dnabank.html). Researchers at the University of Minnesota College of Veterinary Medicine in Saint Paul have studied the possible role of the alpha one antitrypsin gene, which is associated with spontaneous pneumothorax in humans, but have not found a relationship between one of the known mutations in that gene and the condition in dogs.
Principal investigator Vicki Wilkie, D.V.M., Ph.D., DACVS, assistant clinical professor and director of surgery residencies, notes that so far only one mutation in the gene has been studied. "There are over 60 mutations that have been identified in the alpha one antitrypsin gene in humans," she explains. "It is possible that another mutation could be responsible for this condition or there could be different mutations for different breeds and different types of spontaneous pneumothorax."
Though various breeds were included in the study, not many were Siberian Huskies. In order to further the study, Wilkie urges owners of dogs that have suffered spontaneous pneumothorax to contact her at wilke175@umn.edu.
"We would like to obtain a tissue sample if a dog had surgery for this condition," Wilkie says. "If a lung sample was removed, we would like a piece of the archived tissue and a blood sample for DNA and to test for alpha one antitrypsin levels."
Although spontaneous pneumothorax is overrepresented in Siberian Huskies, the condition is a relatively rare disease. Better documented studies, including health surveys, are needed to estimate the prevalence of pneumothorax in the breed. Most Siberian Husky breeders and owners agree that if the disorder affects even one dog, it is one dog too many.
Purina appreciates the support of the Siberian Husky Club of America and particularly Sheila E. (Blanker) Morrissey, D.V.M., SHCA genetics chair, in helping to identify topics for the Purina Pro Club Siberian Husky Update newsletter.