Selective vagal afferent dysfunction in dogs with congenital idiopathic megaoesophagus

Clinicopathologic evaluation of congenital idiopathic megaesophagus in a Gordon Setter puppy: a case report and development and application of peripherin immunohistochemistry for detection of ganglion cells

We examined a case of congenital idiopathic megaesophagus (CIM) in a 5-wk-old female Gordon Setter puppy by means of contrast radiography, autopsy, histopathology, and immunohistochemistry. Clinical and radiologic findings included weight stagnation and marked generalized esophageal dilation with ventral displacement of the heart and lungs. These findings were confirmed at autopsy, and segments of the thoracic esophagus were sampled for histopathology. On histopathology, diffuse esophageal muscular atrophy, mucosal erosions, mononuclear inflammation, and a marked reduction in the number of myenteric plexus structures and number of ganglion cells were present (aganglionosis). The latter was determined immunohistochemically using an anti-peripherin antibody as the primary reagent, which provides a strong tool for the histologic confirmation of CIM. The histologic findings share some similarities to lesions associated with megaesophagus in Friesian foals, as well as esophageal achalasia and Hirschsprung disease in humans.

Use of a videofluoroscopic feeding evaluation to guide management of dogs with congenital idiopathic megaoesophagus

Background

Evidence‐based guidelines for determining dietary management in dogs with megaoesophagus are lacking.

Objectives

This study looked to compare oesophageal clearance times (ECT) of liquid and two food consistencies using a contrast videofluoroscopy feeding evaluation, and to assess if recommendations made based on findings could improve regurgitation and quality of life in dogs with congenital megaoesophagus.

Methods

Twenty‐one dogs with congenital megaoesophagus and nine healthy dogs received liquid, slurry, and meatball diets containing barium while in an upright position. Follow‐up was performed to determine response to recommendations.

Results

Healthy dogs had significantly shorter median ECT for all consistencies (p < 0.001). In the megaoesophagus group, ECT varied by consistency and individual. The number of dogs in the megaoesophagus group with complete clearance was four (median ECT 10 min) for liquid, five (median ECT 5 min) for slurry, and two (median ECT 5 and 30 min, respectively) for meatballs. Partial clearance was seen in 11 dogs (median clearance 25%) with liquid, seven with slurry (median clearance 50%), and five with meatballs (median clearance 60%). Recommendations included altering current medications (13/21 dogs), diet consistency (6/21), time upright (12/21), water delivery (21/21), and adding activity (7/21). Regurgitation episodes/week decreased significantly from 5.5 to 2.5 (p < 0.001) at follow‐up 3–5 weeks post‐evaluation, with 95% of owners reporting improvement in quality of life. Seventy percent were alive 46–777 days after last recheck. Three dogs died from megaoesophagus associated complications (median survival 461 days after diagnosis).

Conclusions

The findings of this study suggest that a videofluoroscopic feeding evaluation may help guide management of dogs with congenital megaoesophagus.

Congenital idiopathic megaesophagus in the German shepherd dog is a sex-differentiated trait and is associated with an intronic variable number tandem repeat in Melanin-Concentrating Hormone Receptor 2

Congenital idiopathic megaesophagus (CIM) is a gastrointestinal (GI) motility disorder of dogs in which reduced peristaltic activity and dilation of the esophagus prevent the normal transport of food into the stomach. Affected puppies regurgitate meals and water, fail to thrive, and experience complications such as aspiration pneumonia that may necessitate euthanasia. The German shepherd dog (GSD) has the highest disease incidence, indicative of a genetic predisposition. Here, we discover that male GSDs are twice as likely to be affected as females and show that the sex bias is independent of body size. We propose that female endogenous factors (e.g., estrogen) are protective via their role in promoting relaxation of the sphincter between the esophagus and stomach, facilitating food passage. A genome-wide association study for CIM revealed an association on canine chromosome 12 (P-val = 3.12x10^-13), with the lead SNPs located upstream or within Melanin-Concentrating Hormone Receptor 2 (MCHR2), a compelling positional candidate gene having a role in appetite, weight, and GI motility. Within the first intron of MCHR2, we identified a 33 bp variable number tandem repeat (VNTR) containing a consensus binding sequence for the T-box family of transcription factors. Across dogs and wolves, the major allele includes two copies of the repeat, whereas the predominant alleles in GSDs have one or three copies. The single-copy allele is strongly associated with CIM (P-val = 1.32x10^-17), with homozygosity for this allele posing the most significant risk. Our findings suggest that the number of T-box protein binding motifs may correlate with MCHR2 expression and that an imbalance of melanin-concentrating hormone plays a role in CIM. We describe herein the first genetic factors identified in CIM: sex and a major locus on chromosome 12, which together predict disease state in the GSD with greater than 75% accuracy.

German shepherd dogs (GSDs) are predisposed to an inherited motility disorder of the esophagus, termed congenital idiopathic megaesophagus (CIM), in which swallowing is ineffective and the esophagus is enlarged. Affected puppies are unable to properly pass food into their stomachs and consequently regurgitate their meals and show a failure to thrive, often leading to euthanasia. Here, we discovered that male GSDs are affected at a ratio of almost 2-to-1 over females, suggesting a protective biological advantage in females. In humans, estrogen is thought to play a role in the male predominance of esophageal disorders like reflux esophagitis and esophageal cancer. In a genome-wide scan, we identified an association with CIM on chromosome 12 and, within this region, a repetitive sequence in MCHR2. This gene encodes a receptor for melanin-concentrating hormone, a signaling molecule that is linked to appetite, weight, and gut motility. Together, sex and the MCHR2 repeat sequence accurately predict affection status in over 75% of dogs, and a genetic test is now available to facilitate breeding decisions aimed at reducing disease incidence.

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.

Clinical features and prognosis of canine megaesophagus in Japan

Megaesophagus (ME) is a common esophageal disease in dogs and the prognosis is generally poor, especially with aspiration pneumonia (AP). We retrospectively investigated the clinical features and prognosis of canine ME in Japan. Twenty-eight dogs were included in this study, with the Miniature Dachshund breed being significantly overrepresented (odds ratio: 4.33). Most cases (21 of 28) were diagnosed as idiopathic ME and Myasthenia gravis was the most common cause of secondary ME. The overall median survival time (MST) was not reached and the 3-month survival rate was 85.7%. Ten dogs were diagnosed with AP, at least once during the study period, and the MST of ME dogs with AP was 114 days. The survival time overall and even with AP, was notably more prolonged compared to the previous studies. We hypothesized that treatment for canine ME could prolong the survival time, even in those with both ME and AP.

Carcinoma in situ within an area of Barrett esophagus in a dog with megaesophagus

A 10-y-old Irish Setter was presented with a history of recurrent episodes of regurgitation and vomiting, with more recent development of tachypnea. Megaesophagus had been diagnosed in the dog 2 y prior to this presentation. A solitary polypoid mass present immediately rostral to the lower esophageal sphincter was biopsied during percutaneous endoscopic gastrostomy tube placement. Barrett esophagus was diagnosed based on the observation of a polypoid mass with intestinal metaplasia that arose from the surrounding esophagus. Histology of the polypoid mass demonstrated squamous-to-columnar metaplasia, hyperplasia, dysplasia, and carcinoma in situ.

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.

SULF1 and SULF2 regulate heparan sulfate-mediated GDNF signaling for esophageal innervation

Heparan sulfate (HS) plays an essential role in extracellular signaling during development. Biochemical studies have established that HS binding to ligands and receptors is regulated by the fine 6-O-sulfated structure of HS; however, mechanisms that control sulfated HS structure and associated signaling functions in vivo are not known. Extracellular HS 6-O-endosulfatases, SULF1 and SULF2, are candidate enzymatic regulators of HS 6-O-sulfated structure and modulate HS-dependent signaling. To investigate Sulf regulation of developmental signaling, we have disrupted Sulf genes in mouse and identified redundant functions of Sulfs in GDNF-dependent neural innervation and enteric glial formation in the esophagus, resulting in esophageal contractile malfunction in Sulf1(-/-);Sulf2(-/-) mice. SULF1 is expressed in GDNF-expressing esophageal muscle and SULF2 in innervating neurons, establishing their direct functions in esophageal innervation. Biochemical and cell signaling studies show that Sulfs are the major regulators of HS 6-O-desulfation, acting to reduce GDNF binding to HS and to enhance GDNF signaling and neurite sprouting in the embryonic esophagus. The functional specificity of Sulfs in GDNF signaling during esophageal innervation was established by showing that the neurite sprouting is selectively dependent on GDNF, but not on neurotrophins or other signaling ligands. These findings provide the first in vivo evidence that Sulfs are essential developmental regulators of cellular HS 6-O-sulfation for matrix transmission and reception of GDNF signal from muscle to innervating neurons.

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

OBJECTIVES

To evaluate whether dogs with megaoesophagus due to myasthenia gravis display less oesophageal dilatation radiographically than dogs with other causes of megaoesophagus.

METHODS

Thoracic radiographs of 66 dogs with megaoesophagus in which concurrent acetylcholine receptor antibody titre was known were analysed retrospectively. Maximum oesophageal diameter was transformed to a "relative oesophageal diameter" using a ratio with thoracic inlet diameter. Dogs were divided into two groups according to "MG" or "non-MG" antibody status and median relative oesophageal diameter values were compared between groups and with age, weight and sex. A receiver operating characteristic plot was used to evaluate a suitable relative oesophageal diameter cut-off.

RESULTS

Twenty dogs were diagnosed with myasthenia gravis and 46 with other causes of megaoesophagus. Thoracic inlet size correlated significantly with bodyweight and surface area (r(2)=0.627 and 0.669, respectively). Median values of relative oesophageal diameter for the MG group and non-MG group were 0.58 and 0.66, respectively, and these showed a small, but significant, difference (P=0.029), although there was complete overlap in the range of relative oesophageal diameter values between groups. There was no significant association between relative oesophageal diameter and sex, age or weight or significant difference in age, sex or weight between the two groups. An increased odds ratio for myasthenia gravis existed in golden retrievers and German shepherd dogs.

CLINICAL SIGNIFICANCE

Relative oesophageal diameter appears to be of limited diagnostic utility in distinguishing dogs with megaoesophagus due to myasthenia gravis from those with megaoesophagus due to other causes.

Innervation of the mammalian esophagus

Understanding the innervation of the esophagus is a prerequisite for successful treatment of a variety of disorders, e.g., dysphagia, achalasia, gastroesophageal reflux disease (GERD) and non-cardiac chest pain. Although, at first glance, functions of the esophagus are relatively simple, their neuronal control is considerably complex. Vagal motor neurons of the nucleus ambiguus and preganglionic neurons of the dorsal motor nucleus innervate striated and smooth muscle, respectively. Myenteric neurons represent the interface between the dorsal motor nucleus and smooth muscle but they are also involved in striated muscle innervation. Intraganglionic laminar endings (IGLEs) represent mechanosensory vagal afferent terminals. They also establish intricate connections with enteric neurons. Afferent information is implemented by the swallowing central pattern generator in the brainstem, which generates and coordinates deglutitive activity in both striated and smooth esophageal muscle and orchestrates esophageal sphincters as well as gastric adaptive relaxation. Disturbed excitation/inhibition balance in the lower esophageal sphincter results in motility disorders, e.g., achalasia and GERD. Loss of mechanosensory afferents disrupts adaptation of deglutitive motor programs to bolus variables, eventually leading to megaesophagus. Both spinal and vagal afferents appear to contribute to painful sensations, e.g., non-cardiac chest pain. Extrinsic and intrinsic neurons may be involved in intramural reflexes using acetylcholine, nitric oxide, substance P, CGRP and glutamate as main transmitters. In addition, other molecules, e.g., ATP, GABA and probably also inflammatory cytokines, may modulate these neuronal functions.

Gastrointestinal motility disorders and gastrointestinal prokinetic therapy

Gastrointestinal motility disorders represent a diagnostic and therapeutic challenge. Disorders of gastrointestinal motility may result in accelerated transit, delayed transit, impaired relaxation, or inappropriate relaxation. The delayed transit disorders are the most important motility disorders of companion animals and may involve the esophagus (hypomotility and megaesophagus), stomach (delayed gastric emptying), small intestine (postoperative ileus and intestinal pseudo-obstruction), or colon (constipation and megacolon).