Use of radiographic measurements in distinguishing myasthenia gravis from other causes of canine megaoesophagus

Radiographic vertical tracheal diameter assessment at different levels along the trachea as an alternative method for the evaluation of the tracheal diameter in non-brachycephalic small breed dogs

Background

Tracheal narrowing due to congenital tracheal hypoplasia, acquired tracheal stenosis and tracheal collapse can lead to life-threatening respiratory distress. Tracheal hypoplasia has been identified in brachycephalic dog breeds, predominantly English Bulldogs, by measuring the tracheal diameter compared to the diameter of the thoracic inlet and creating a ratio. However, reference ranges for tracheal diameter have not been established for non-brachycephalic small breed dogs. It would be advantageous to have established tracheal diameters for non-brachycephalic small breed dogs, as these are the dogs most at risk of tracheal collapse. The main objective, of this study was to radiographically evaluate vertical tracheal diameter (VTD) at three standardized locations along the trachea of non-brachycephalic small breed dogs, in an attempt to further establish a screening diagnostic protocol for canine tracheal hypoplasia. Medical records and thoracic radiographs of non-brachycephalic small breed dogs without respiratory disease were reviewed. Right lateral radiographs were reviewed. The absolute and average VTDs at three locations (location A: caudal cervical VTD; location B thoracic inlet VTD; location C: intrathoracic VTD) were standardized by manubrium length (ML), as well as by the previously utilized thoracic inlet distance (Ti-D) and proximal 3rd rib width (PR3-W) to calculate manubrium-tracheal index (M-TI), thoracic inlet-tracheal index (Ti-TI), and proximal R3-tracheal score (PR3-TS), respectively. Correlations between averaged tracheal diameter and each of the ML, Ti-D, and PR3-W, and between M-TI and each of Ti-TI and PR3-TS were calculated.

Results

Eighty-one healthy dogs met the criteria for inclusion. Significant differences (P < 0.0001) were identified among the mean values of the absolute and standardized VTDs at levels A, B, and C. The smallest tracheal diameter was identified at the level of the thoracic inlet (Level B).

The average VTD correlated better with ML (r_s = 0.82, P < 0.0001) compared to Ti-D and PR3-W. A relatively strong correlation (r_s = 0.77, P < 0.0001) was identified between the averaged manubrium tracheal index (M-TI) and thoracic inlet tracheal index (Ti-TI).

Conclusion

M-TI is an appropriate alternative to Ti-TI and PR3-TS to radiographically evaluate VTD in dogs. M-TI < 0.43, < 0.34, or < 0.38 at level A, B, or C, respectively, may indicate tracheal hypoplasia in non-brachycephalic small breed dogs. Screening of canine VTD could be achieved using M-TI.

Canine Nonstructural Megaesophagus as a Clinical Sign of Potential Neurological Disease: 99 Cases

Knowledge regarding the etiology and prognosis for canine megaesophagus (ME) is currently limited to small case series that may now be out of date in light of recent advances in the understanding of neurological syndromes and the availability of advanced diagnostic testing. Ninety-nine dogs diagnosed with nonstructural ME were included. Congenital idiopathic ME was present in 10 cases, with complete resolution of clinical signs in a single case. Eighty-nine cases were considered acquired, with most cases being either idiopathic (42.7%) or associated with myasthenia gravis (38.2%). Idiopathic cases represented a smaller percentage of acquired ME than previously reported. Death or euthanasia directly related to ME occurred in almost 50% of acquired cases, whereas clinical signs persisted in ∼20% of cases and resolved in 30% of cases. A diagnosis of an underlying etiology, in particular myasthenia gravis, was associated with a better outcome in acquired ME. ME continues to be a challenging condition to manage, with a guarded-to-poor prognosis, particularly when an underlying etiology is not identified. Thorough diagnostic testing for an underlying neurological disorder is important in cases with ME as this may allow institution of appropriate treatment and the potential for a better prognosis.

Survey of owners on population characteristics, diagnosis, and environmental, health, and disease associations in dogs with megaesophagus

Megaesophagus affects dogs worldwide but limited information is available regarding its characteristics in the general population of dogs. The objectives of this study were to provide information on a large population of dogs diagnosed with megaesophagus in regards to population characteristics, medical and family history, diagnosis, concurrent disease, and predisposing factors. A link to a web-based survey was provided on megaesophagus support websites and 838 eligible surveys were evaluated. Breeds most frequently associated with congenital megaesophagus were German shepherds, mixed breed "goldendoodles", Labrador retrievers, great Danes, and dachshunds. Breeds most often associated with acquired megaesophagus were Labrador and golden retrievers, Chihuahuas, boxers, German shepherds, dachshunds, and Rottweilers. Diagnosis was most often by a general practitioner (63.6%) via plain radiographs (63.3%) and/or barium study (45%). Congenital megaesophagus was diagnosed in 41.3% of dogs and persistent right aortic arch in 4.3%. Diseases most commonly associated with acquired megaesophagus were myasthenia gravis (19.3%), esophagitis (10.8%), hypothyroidism (8.8%). Survey results support previous breed predilections and identified dachshunds, boxers, Chihuahuas, Rottweilers, and "goldendoodles" as additional at risk breeds. Myasthenia gravis was found at lower rates than previous described and contrary to recent studies, hypothyroidism was found in relatively high prevalence. Most dogs were diagnosed by a general practitioner suggesting previous studies at referral facilities may be biased towards dogs with more severe disease and worse outcomes.

Sildenafil improves clinical signs and radiographic features in dogs with congenital idiopathic megaoesophagus: a randomised controlled trial

We evaluated the efficacy of oral sildenafil citrate in dogs with congenital idiopathic megaoesophagus (CIM). Twenty-one puppies were randomly assigned to two groups (treatment and control). The dogs were given sildenafil oral suspension 1 mg/kg every 12 hours for 14 days or placebo in a masked fashion. Clinical signs (frequency of regurgitation and weight gain) and oesophagrams (relative oesophageal diameter, ROD) were evaluated in order to assess the efficacy of drug treatment, by examiners who were unaware of the study protocol. In addition, a set of in vitro experiments on isolated samples of canine lower oesophageal sphincter (LOS) was performed, and the effects of increasing concentrations of sildenafil on basal tone and electrically-stimulated motility were assessed. Sildenafil administration significantly reduced the number of regurgitation episodes (0.88±1.40 v 2.65±1.56, P<0.0001) and significantly increased weight gain in the treated dogs compared to controls (79.76±28.30 per cent v 53.40±19.30 per cent, P=0.034). ROD values, at the end of the treatment period, were significantly decreased in the sildenafil group, compared to pre-treatment values (0.97±0.19 v 0.24±0.14, P<0.0001), in contrast to control subjects (0.98±0.17 v 1.10±0.25, P=0.480). In accordance with the in vivo findings, sildenafil dose-dependently reduced basal tone and increased electrically-induced relaxation of dog LOS samples. These results suggest that sildenafil citrate helps ameliorate clinical and radiographic signs in dogs with CIM by reducing LOS tone, and could represent a novel therapeutic tool for the treatment of this disease.

Long-term management of a dog with idiopathic megaesophagus and recurrent aspiration pneumonia by use of an indwelling esophagostomy tube for suction of esophageal content and esophagogastric tube feeding

A 10-year-old neutered male Labrador Retriever dog was diagnosed with idiopathic megaesophagus. Despite receiving conventional treatments including elevated feeding, the dog showed repeated regurgitation and aspiration pneumonia, consequently developing weight loss and severe malnutrition. For the purpose of controlling regurgitation, an esophagostomy tube was placed for draining the esophageal fluid. Additionally, an esophagogastric tube was placed for nutritional support. After tube placement, the average frequency of regurgitation was reduced from 2.4 times a day to 0.1 times a day. The nutritional state of the dog improved gradually, and the body weight increased from 18.5 to 27.9 kg. The dog died on day 951, and necropsy revealed a gastric ulcer (2.5 cm in diameter), presumably esophagostomy tube-induced injury. This case report suggests that patients with idiopathic megaesophagus and persistent regurgitation might benefit from esophageal drainage through an esophagostomy tube.

Diagnostic accuracy of tests based on radiologic measurements of dogs and cats: a systematic review

A systematic review of diagnostic tests based on radiologic measurements of structures in dogs and cats was done in order to reach generalizable conclusions about the value of making such measurements. Literature search was done using the ISI Web of Knowledge(SM) for studies in the subject category Veterinary sciences. Studies were eligible for inclusion that employed length, angle, area or volume measurements from radiographic, ultrasonographic, CT or MR images of dogs or cats as a diagnostic test for a naturally occurring condition, compared the results of imaging with a reference standard, included at least 10 subjects, and sufficient data that a 2 × 2 table of results could be constructed. Quality of studies was assessed using the QUADAS-2 tool. Twenty-six studies were found describing 40 tests that satisfied the inclusion criteria. Tests were radiographic in 22 (55%) instances and ultrasonographic in 18 (45%). Quality of studies was generally low, with a risk of bias in patient selection in 92% studies, performance of the index test in 73% studies, and patient flow in 42% studies. Median (range) number of subjects was 64 (20-305), sensitivity was 77% (38-99%), specificity was 82% (50-99%), positive likelihood ratio was 4.1 (1-103), and negative likelihood ratio was 0.29 (0.01-1). Two studies that compared accuracy of radiographic measurements to subjective image interpretation alone found no difference. Evidence is weak that radiologic measurements of structures in dogs and cats are useful for diagnosis, hence measurements should not be emphasized as a basis for diagnosis in either teaching or clinical imaging reports.

Imaging evaluation of dogs and cats with Dysphagia

The current literature is reviewed in this paper regarding the application of diagnostic imaging in the evaluation of swallowing disorders of the dog. The applications of radiography, contrast radiography, and contrast videofluoroscopy are discussed with pertinent case examples provided for emphasis. The indications for image-guided interventions are also described.

Clinical factors associated with death before discharge and overall survival time in dogs with generalized megaesophagus

OBJECTIVE

To investigate the association of 6 clinical features with outcome of dogs with generalized megaesophagus.

DESIGN

Retrospective cohort study.

ANIMALS

71 client-owned dogs with radiographic evidence of generalized esophageal dilation.

PROCEDURES

Medical records were reviewed for data on signalment, age at onset of clinical signs, body weight, evidence of undernutrition, and the administration of drugs to treat or prevent esophagitis. Radiographs were reviewed for evidence of aspiration pneumonia (AP) and to calculate the relative esophageal diameter. Details of outcome were collected from the medical records and by contacting owners and referring veterinarians. The association of 6 factors with death before discharge and overall survival time was assessed.

RESULTS

Overall median survival time was 90 days. Nineteen (26.7%) patients died before discharge from the hospital. Radiographic evidence of AP was both positively associated with death before discharge and negatively associated with overall survival time. An age at onset of clinical signs of >13 months was negatively associated with overall survival time. No evidence of an association of the degree of esophageal dilation or the use of drugs to prevent or treat esophagitis with death before discharge or overall survival time was found.

CONCLUSIONS AND CLINICAL RELEVANCE

Radiographic evidence of AP and the age at onset of clinical signs were the only variables found to be significantly associated with survival time in this study, and this should be considered when advising on prognosis in dogs with megaesophagus.