History
A 1-year-old 39.0-kg (85.8-lb) sexually intact male Labrador Retriever was admitted to the internal medicine service of the veterinary teaching hospital at Mississippi State University for evaluation of coughing of 1 month's duration.
Three months prior to referral, a cutaneous mass was excised from the patient's thoracic wall. The mass was on the right side of the ventral portion of the thorax. It was described as a small draining tract that contained white necrotic tissue. Cytologic evaluation of an impression smear obtained from the draining lesion revealed the presence of neutrophils. The dog was treated with antimicrobials for approximately 1 week. Because of the lack of improvement, the mass was excised. Histologic evaluation of the mass revealed organisms consistent with Pythium insidiosum. Positive results on a whole blood ELISA for anti–P insidiosum antibodies confirmed the diagnosis of pythiosis. The dog underwent a course of treatment with an immunotherapy druga that contained purified P insidiosum antigens to induce a T-helper 1 cell immune response. The patient's surgical site healed without complication.
Approximately 2 months after the mass was removed, the dog developed a cough that worsened with excitement and when rising from a recumbent position. The patient also had weight loss and a decreased appetite. The primary care veterinarian performed thoracic radiography that revealed an increase in soft tissue opacity in the area of the right caudal lung lobe. The patient was treated for suspected pneumonia, along with treatments for concurrent otitis, and was referred for further evaluation.
On physical examination, a loud, productive cough was noted along with harsh lung sounds on auscultation of the right side of the thorax. The CBC revealed neutrophilia (13,510 neutrophils/μL; reference interval, 3,000 to 11,500 neutrophils/μL) and eosinophilia (3,281 eosinophils/μL; reference interval, 100 to 1,250/μL). Serum biochemical analysis revealed hyperglobulinemia (6.5 g/dL; reference interval, 2.1 to 4.3 g/dL) and hypoalbuminemia (2 g/dL; reference interval, 2.5 to 3.9 g/dL). Four-view thoracic radiography was performed (Figure 1; left lateral and dorsoventral views are provided).
Left lateral (A) and dorsoventral (B) radiographic views of the thorax of a 1-year-old 39.0-kg (85.8-lb) sexually intact male Labrador Retriever evaluated for coughing of 1 month's duration.
Citation: Journal of the American Veterinary Medical Association 250, 11; 10.2460/javma.250.11.1231
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
On the left lateral projection, there is increased soft tissue opacity present in the area of the tracheobronchial lymph nodes causing ventral displacement of the mainstem bronchi, and increased soft tissue opacity of the right caudal lung lobe. There is also a lobar sign present at the cranial margin of the right caudal lung lobe. The dorsoventral view reveals border effacement of the right caudal aspect of the cardiac silhouette and right aspect of the diaphragm as a result of an alveolar pattern in the right caudal lung lobe (Figure 2). Air bronchograms are noted, and a lobar sign is present along the cranial margin of the right caudal lung lobe and along the medial margin of the right caudal lung lobe where it abuts the accessory lung lobe. There is a mild mediastinal shift to the left, away from the affected lung lobe, which is evidenced by the leftward shift of the carina and of the thoracic trachea to midline. There is also a diffuse increase in soft tissue opacity throughout the thorax that may be the result of a mild unstructured interstitial pulmonary pattern or attributable to the patient's body condition. The mass in the right caudal lung lobe along with tracheobronchial lymphadenopathy may be the result of granulomatous disease or primary pulmonary neoplasia with metastasis to the tracheobronchial lymph nodes. Considering the history, the most likely diagnosis is a Pythium infection with lymphatic spread to the tracheobronchial lymph nodes and lungs.
Same radiographic images as in Figure 1. A—Notice the increase in soft tissue opacity in the area of the tracheobronchial lymph nodes (black oval). There is a lobar sign at the cranial margin of the right caudal lung lobe (white arrow). B— There is border effacement of the cardiac silhouette and an alveolar pattern of the right caudal lung lobe, with air bronchograms (black arrows) and a lobar sign (white arrows).
Citation: Journal of the American Veterinary Medical Association 250, 11; 10.2460/javma.250.11.1231
Treatment and Outcome
Abdominal radiography and ultrasonography were performed to further investigate the dog's signs of lethargy and inappetence. Diagnostic imaging of the abdomen revealed few additional abnormalities including splenomegaly and lymphadenopathy of jejunal and medial iliac lymph nodes. Ultrasound-guided fine-needle aspiration was performed to obtain samples for cytologic evaluation of the spleen, a jejunal lymph node, and the right caudal lung lobe.
The dog underwent bronchoscopy while under general anesthesia. There was compression of the airways at the mainstem bronchi, and the airways of the right lung were swollen and irregular. A bronchoalveolar lavage was performed on both the left and right lungs. The left bronchoalveolar lavage revealed marked eosinophilic to mild purulent inflammation, and the right had marked purulent inflammation with 77% neutrophils and 19% alveolar macrophages. The macrophages contained phagocytized material (hemosiderin), which indicated there had been chronic hemorrhage.
Cytologic evaluation of fine-needle aspirates of the right caudal lung lobe revealed pyogranulomatous to eosinophilic inflammation with intralesional hyphal structures. Gomori methenamine silver staining was performed and revealed broad, poorly septated hyphal elements consistent with P insidiosum.
The invasiveness of the disease did not allow for surgical resection. For symptomatic treatment, hydrocodone was administered for the cough. Additional information was not available because the patient was lost to follow-up.
Comments
Pythium insidiosum is an oomycete frequently associated with tropical to subtropical aquatic environments. The dog of the present report was used for duck hunting and was regularly exposed to water. In the United States, pythiosis is most commonly seen in the Gulf Coast states, although it has been reported on the East Coast and West Coast and in the Midwest.1 It can often cause fatal disease, which manifests as gastrointestinal or cutaneous lesions. Cutaneous pythiosis is thought to occur by direct contact of the oomycete with damaged skin, where encystation and invasion take place.1 Gastrointestinal pythiosis is the most common form of the disease and carries a grave prognosis. Although the transmission is poorly understood, the frequent occurrence of gastrointestinal pythiosis may be explained by the consumption of stagnant water or eating grass containing P insidiosum, which may then invade damaged gastrointestinal mucosa.2
Findings in 1 study3 revealed that the median survival time in 10 dogs with the gastrointestinal form of pythiosis was 26 days, with no long-term survivors. However, in 1 clinical report,4 an affected dog that was treated by a combination of marginal excision of the gastrointestinal mural lesions and medical treatment achieved a long-term survival time of at least 2 years.
Extension of cutaneous pythiosis into lymph nodes is rare, but is presumed to have occurred in the dog of the present report. This dog had a confirmed cutaneous Pythium infection with subsequent development of respiratory disease and confirmation of Pythium infection in the lungs.
Footnotes
Pythium Immunotherapy, Pan American Veterinary Laboratories, Hutto, Tex.
References
1. Grooters AM. Pythiosis, lagenidiosis, and zygomycosis. In: Sykes JE, ed. Canine and feline infectious diseases. St Louis: Elsevier Saunders, 2014; 668–678.
2. Pan American Veterinary Labs website. Epidemiology of pythium. Available at: pythium.pavlab.com/subpage1.html. Accessed Jul 10, 2016.
3. Berryessa NA, Marks SL, Pesavento PA, et al. Gastrointestinal pythiosis in 10 dogs from California. J Vet Intern Med 2008; 22: 1065–1069.
4. Schmiedt CW, Stratton-Phelps M, Torres BT, et al. Treatment of intestinal pythiosis in a dog with a combination of marginal excision, chemotherapy, and immunotherapy. J Am Vet Med Assoc 2012; 241: 358–363.
