Companion May 2012 - BSAVA

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Clinical conundrum Rebecca Thorne, intern at Davies Veterinary Specialists invites companion readers to consider the approach to a tachypnoeic older Labrador retriever 12 | companion Case presentation An 11-year-old, male neutered, Labrador retriever presented with a reduced appetite and lethargy of several weeks duration. Clinical examination was mostly unremarkable, but the dog was tachypnoeic (RR 50 breaths pm) with increased effort but reduced depth of inspiration. On thoracic auscultation cardiac sounds were noted in a more caudal location than normal and the cranial thorax seemed dull on percussion. Create a problem list for this patient ■■ Tachypnoea and increased effort ■■ Lethargy ■■ Decreased appetite ■■ Caudally displaced heart sounds ■■ Dull thoracic percussion Create a list of likely differential diagnoses for this case Tachypnoea and increased effort could have a multitude of aetiologies. They can be considered in light of the anatomical area of the airway involved. Small airway disease ■■ Foreign body Pulmonary parenchymal disease ■■ Neoplasia ■■ Haemorrhage ■■ Pulmonary fibrosis ■■ Infectious disease, eg: Bordetella bronchiseptica ■■ Pulmonary oedema ■■ Thromboembolism ■■ Parasitic eg: Angiostrongylus vasorum Thoracic tracheal disease ■■ Extra-luminal compression ■■ Tracheal collapse ■■ Neoplasia Pleural (restrictive) disease: ■■ Neoplasia: mediastinal, thoracic wall ■■ Pleural effusion – pyo-, chylo-, haemo-thorax ■■ Diaphragmatic hernia or rupture The differential diagnosis list can be further refined on the basis of the pattern of respiration observed. Upper respiratory tract disease (nasal passages, pharynx, larynx and trachea) was less likely as the dog was showing no clinical signs of stertor or stridor and the dyspnoea was not primarily inspiratory. This was considered an important rule out as laryngeal paralysis would be a common differential for respiratory distress in an older Labrador retriever. Parenchymal lung diseases were considered less likely as these are often associated with a mixed pattern with both inspiratory and expiratory effort, which was not seen in this case. Similarly small airway disease was unlikely as it is typified by a short inspiratory and prolonged expiratory phase. This patient’s respiratory pattern could be described as restrictive, an increased respiratory rate with reduced depth of inspiration, which is most consistent with pleural space disease. However, these signs might be attributable to anaemia and this possibility cannot be excluded at this stage. In support of this suspicion the caudally displaced heart sounds suggests a space occupying lesion in the cranial thorax displacing the heart and this would also be consistent with dull thoracic percussion. Lethargy could be attributed to the tachypnoea, increased respiratory effort and reduced respiratory capacity. Decreased appetite is a fairly non specific clinical sign, particularly in this case which has evidence of other disease and was not considered further in isolation. In summary the patient’s respiratory pattern suggests a pleural space disease, supported by apparent displacement of the heart on auscultation and dull thoracic percusion. As such the most likely differential would be a large space occupying thoracic mass.
What initial investigations would you consider? A blood sample was taken for routine haematology and biochemistry as it was anticipated that the further investigation would require sedation or anaesthesia and the patient was geriatric. This also allowed checking of a PCV, in light of the possibility of anaemia. The blood results were unremarkable apart from a mild normocytic normochromic anaemia (PCV = 29) which was of insufficient severity to account for the tachypnoea. Investigation of thoracic disease commenced with radiographs of the thorax to investigate the respiratory signs. As a single diagnostic procedure this was most likely to direct further appropriate investigation, based on the findings. Other investigations that might have been informative, such as pulse oximetry or performing an arterial blood gas analysis, might be indicated based on the findings of thoracic radiography. What is your interpretation of the right lateral thoracic radiograph (Figure 1)? The thoracic image shows a large cranial thoracic “mass” of soft tissue or fluid radiopacity which is displacing and compressing the trachea dorsally and the lung lobes to the caudo-dorsal thorax. The “mass” extends from the thoracic inlet to the 5th intercostal space and displaces the cardiac silhouette, which is somewhat more upright than usual, caudally. An orthogonal view (eg a DV thoracic radiograph) would have been required to definitively locate the ”mass” but based on the presence of tracheal elevation a mediastinal origin seemed most likely. Figure 1: Right lateral thoracic radiograph In light of the radiographic findings refine your differential diagnosis list Mediastinal mass ■■ Mediastinal cyst ■■ Non-neoplastic mediastinal masses (abscess, lymphadenopathy, haematoma) ■■ Mediastinal neoplasia – ■ Lymphoma – ■ Thymoma – ■ Heart base tumour – ■ Metastatic neoplasia How would you narrow you differential diagnoses? Further diagnostically useful information is likely to be gained from ultrasonographic evaluation of the mass, and this would also allow decision making regarding sampling strategy. For example masses may be seen to be highly vascular, precluding a Tru-cut biopsy, or cystic, allowing directed sampling by fine needle aspiration. In this case a large heterogeneous mass of variable echotexture and echogenicity was visualised arising from, and obliterating, the cranial mediastinum. There were numerous vacuolations throughout the mass. Fine needle aspirates under ultrasound guidance were performed from the solid portions of the mass and these were examined. Figure 2: Cytology from mediastinal mass (x200) Courtesy of PTDS companion | 13
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Companion May 2012 - BSAVA

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