CVC highlight: The hunt for grass awns
Saturday, May 10, at the CVC in Washington, D.C., Emily Klocke, DVM, DACVS, took attendees through the havoc wreaked by migrating plant foreign bodies, particularly in hunting dogs.
How they get in
Grass awns and plant material enter the mouth when a dog is breathing hard as it runs through a field. The plant material can migrate through the respiratory tract or other tissues, or it can penetrate through the skin and migrate elsewhere. Grass awns have sharp points that enable skin penetration as well as backward-pointing barbs that prevent retrograde movement.
What owners may notice
Clinical signs will depend on the location of the plant material. Patients may have an interdigital swelling or a draining tract when the paw is affected. Lumbar pain or swelling and pain at the costal region may be present. Other signs of a plant foreign body include a superficial abscess that is drained and treated with antibiotics but then recurs soon after the antibiotics are finished and increased respiratory effort or dyspnea when a pyothorax or pneumothorax is present. Signs can also be vague, such as decreased performance, decreased exercise tolerance, lethargy, fever, and weight loss.
The second wave of invasion—and how to attack it
Bacterial organisms commonly associated with migrating grass awns include Escherichia coli and Actinomyces, Nocardia, Staphyloccocus, Streptococcus, and Pasteurella species. Actinomyces and Nocardia species are often seen as filamentous rods on cytologic examination of fluid. They can be difficult to culture, particularly if antibiotics have been administered before obtaining the sample. So any patient that has a confirmed migrating grass awn but a negative culture result should still be considered to have a bacterial infection and be treated empirically, making sure that antibiotics chosen are appropriate for Actinomyces and Nocardia species, says Dr. Klocke.
Penicillin derivatives are generally a good first choice. Dr. Klocke typically starts with amoxicillin-clavulanic acid orally or amoxicillin-sulbactam intravenously. Administer the antibiotics long-term—four to six weeks depending on the primary problem—but for no less than four weeks. If culture results do show growth, base your antibiotic selection on the sensitivity.
The real hunt begins—and the tools to conquer
A migrating grass awn should be high on your differential list for any hunting dog showing the clinical signs listed above. Physical examination findings (e.g. a subcutaneous abscess, pain on lumbar palpation, decreased lung sounds) will narrow where to look for the problem. A baseline complete blood count may demonstrate a leukocytosis or left shift. Imaging will be the most beneficial diagnostic tool.
For abscesses in hunting dogs, Dr. Klocke says ultrasonographic examination has been extremely useful in identifying and confirming a foreign body in her clinic. A skilled ultrasonographer who has experience locating these types of foreign bodies can help the surgeon to know the exact location of it using anatomical landmarks and give information regarding the size of the foreign body and whether multiple foreign bodies are present. If locating it intraoperatively is difficult, intraoperative ultrasonography can be done. Once the foreign body is located by ultrasound, a needle can be inserted with ultrasonographic guidance to pinpoint its location.
• Respiratory migration
For dogs presenting with respiratory signs, thoracic radiography often reveals pleural effusion, and thoracocentesis is performed to analyze the fluid. Fluid analysis helps in the diagnosis of pyothorax in many of these cases.
A variety of treatment regimens have been recommended, including thoracocentesis, thoracic drain placement with lavage, and thoracotomy. Determining which treatment is appropriate depends on many factors.
If the foreign body has been present for some time, significant loculation can occur from fibrinous deposits that results in the formation of fluid pockets that can be difficult to drain, leading to failure of medical management. Surgical exploration and débridement of the thoracic cavity through a median sternotomy is often recommended in these cases. A foreign body is rarely found, but the débridement and lavage is beneficial in resolving the pyothorax. Leave thoracic drains in place after the surgery to facilitate continued lavage and drainage of the thorax.
Surgery is also indicated if a pulmonary abscess, lung lobe torsion, or foreign body is identified. Ultrasonographic examinations or computed tomography scans of the thoracic cavity can be helpful in identifying these pathologic conditions.