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Basics ⬇

Basics

Definition

A focal or generalized, diffuse dilation of the esophagus with decreased to absent peristalsis.

Pathophysiology

  • In the normal esophagus, the presence of a food bolus in the proximal esophagus stimulates afferent sensory neurons.
  • Signals are transferred centrally, via the vagus and glossopharyngeal nerves to the tractus solitarius and nucleus ambiguus.
  • Motor impulses travel back via the efferent neurons of the vagus nerve to stimulate striated muscle (canine) and striated and smooth muscle (feline) esophageal contraction.
  • Lesions anywhere along this pathway may lead to megaesophagus and resultant retention of food and liquids.
  • There is evidence that afferent nerve dysfunction is the most common lesion in idiopathic cases of megaesophagus. Focal megaesophagus is typically caused by esophageal obstruction distal to the dilated portion of esophagus.

Systems Affected

  • Gastrointestinal-dysphagia, regurgitation, weight loss.
  • Musculoskeletal-weakness, weight loss, exercise intolerance, dysphonia.
  • Nervous-possible manifestation of systemic neurologic/neuromuscular disorder.
  • Respiratory-aspiration pneumonia, coughing.

Genetics

  • Congenital form-megaesophagus can be inherited in wirehaired fox terriers (autosomal recessive) and miniature schnauzers (autosomal dominant or 60% penetrance autosomal recessive).
  • Other breeds reported include dachshund, German shepherd, Great Dane, Irish setter, Labrador retriever, pug, and Chinese shar-Pei.
  • Myasthenia gravis may be congenital in Jack Russell terriers, springer spaniels, smooth fox terriers, dachshunds, and Samoyeds.
  • Acquired form-many diseases, especially neuromuscular diseases, may have an association with megaesophagus. Genetic predispositions for such diseases are listed under each disease separately.

Incidence/Prevalence

  • Congenital forms-rare
  • Acquired disease-uncommon in the dog and rare in the cat.

Signalment

Species

Dogs are more commonly affected than cats

Breed Predilections

  • Dogs-see “Genetics”
  • Cats-Siamese and Siamese-related cats

Mean Age and Range

  • Congenital cases present soon after birth or at weaning during transition from liquid diets to solid foods.
  • Acquired cases may be seen at any age, depending on the etiology.

Signs

Historical Findings

  • Owners often report vomiting; the veterinarian must differentiate vomiting from regurgitation.
  • Regurgitation (considered the hallmark sign); dysphagia; coughing/nasal discharge with aspiration pneumonia; ravenous appetite or inappetence; weight loss or poor growth; ptyalism, and halitosis. Dysphonia may occur secondary to neuromuscular disease.
  • Other signs depend upon underlying etiology.

Physical Examination Findings

  • Cervical swelling may be noted, representing a distended cervical esophagus; ptyalism; halitosis; increased respiratory noises, nasal discharge, and fever (if concurrent pneumonia); cachexia; weakness; weight loss.
  • Assess for concurrent neurologic deficits that may indicate generalized disease. Special attention should be paid to cranial nerves IX, X, and XI. Muscle atrophy (if present) may be focal or generalized.

Causes

Congenital

Idiopathic megaesophagus; congenital MG (rare)

Acquired/Adult Onset

  • Idiopathic (most common).
  • Neuromuscular disease-MG, focal or generalized (25% of cases in dogs); SLE; myositis/myopathic disease; dysautonomia (more common in cats); botulism; vagal dysfunction/damage (bilateral); a possible association between laryngeal paralysis and esophageal dysmotility secondary to polyneuropathy has been identified.
  • Brainstem disease-disease involving CN IX, X nuclei or peripheral nerves.
  • Esophageal obstruction-vascular ring anomaly; esophageal or periesophageal neoplasia (e.g., lymphoma, leiomyoma); stricture; foreign body; granuloma.
  • Toxicity-lead, thallium, anticholinesterase; acrylamide.
  • Endocrine disease-hypoadrenocorticism, hypothyroidism (controversial). Thymoma is associated with MG and megaesophagus in approximately 25% of cats.
  • Miscellaneous-gastric dilatation volvulus, hiatal hernia, gastroesophageal intussusception; esophagitis (gastroesophageal reflux, parasitic infection).

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Must distinguish regurgitation from vomiting.
  • Regurgitation-passive; little to no abdominal effort; no prodromal phase; regurgitated material has increased amounts of thick mucus.
  • Vomiting-active process; prodromal phase; vomited material may have increased bile staining.
  • The shape of the expelled material, presence of undigested food, and length of time from ingestion to regurgitation or vomiting are less helpful to differentiate.

CBC/Biochemistry/Urinalysis

  • May be normal.
  • Inflammatory leukogram may be seen with pneumonia.
  • Other changes may identify underlying etiology-basophilic stippling on red blood cells with lead toxicity; electrolyte disturbances with hypoadrenocorticism; hypercholesterolemia with hypothyroidism; elevated creatine kinase with myopathic disease.

Other Laboratory Tests

  • Acetylcholine receptor antibody titer in all cases of megaesophagus (screen for MG). Approximately 2% of dogs with generalized MG are seronegative; testing should be repeated 2–3 months later, particularly if initial antibody titer is only slightly below the reference interval.
  • ACTH stimulation test or baseline cortisol level for hypoadrenocorticism.
  • Thyroid panel for hypothyroidism (may be affected by concurrent disease).
  • Blood and urine lead levels.
  • ANA titers for SLE.
  • Blood cholinesterase levels for organophosphate toxicity.

Imaging

Survey Thoracic Radiographs

  • Dilated esophagus filled with air, fluid, or food. Interpret thoracic radiographs in anesthetized animals and anxious or painful animals with caution in light of aerophagia that can cause distention of the esophagus with air.
  • Evidence of aspiration pneumonia.
  • Ventral displacement of the trachea on lateral radiographs.
  • Ventrodorsal radiographs may show lateral tracheal displacement.
  • Evidence of underlying etiology: mediastinal mass (thymoma), hiatal hernia, neoplasia, etc.
  • Radiographs do not differentiate dogs with megaesophagus due to MG from dogs with megaesophagus due to other etiologies.

Contrast Esophagram and Video-Fluoroscopy

  • Barium liquid and barium meal may demonstrate abnormal pooling, poor motility, or structural lesions. Iohexol may be used if perforation is a concern.
  • Use with caution in animals with megaesophagus due to risk of aspiration of contrast material.
  • Exercise extreme caution in animals with radiographic evidence of pneumonia.
  • Monitor animals closely after radiographs for signs of aspiration.
  • Videofluoroscopy-may be used to assess primary and secondary esophageal peristalsis. May help determine the best food consistency for long-term management.

Diagnostic Procedures

  • Esophagoscopy-may be used for foreign body retrieval, evaluation of suspected obstructive lesions, neoplasia, or esophagitis. Distal esophageal neoplasia may mimic idiopathic megaesophagus and may require endoscopy for diagnosis.
  • Electrophysiology-in cases of suspected neuromuscular disease, may be used in conjunction with muscle and nerve biopsies.
  • Additional tests-may be indicated in cases of CNS disease: CSF analysis, distemper titers, brain CT or MRI.
  • Fecal exam-may indicate Spirocerca lupi infection.

Pathologic Findings

Depend upon underlying etiology and presence of complicating factors.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Treat underlying etiology (when applicable).
  • Most important aspects are meeting nutritional requirements and treating or preventing aspiration pneumonia.

Nursing Care

  • Aspiration pneumonia may require oxygen therapy, nebulization/coupage, fluid therapy with balanced electrolyte solution.
  • These animals may be recumbent and require soft bedding and should be maintained in sternal recumbency or turned to alternate down side every 4 hours.

Activity

Depending on etiology, restricted activity is not necessary.

Diet

  • Calculate precise nutritional requirements, including degree of debilitation.
  • Experimentation with different food consistencies is essential (e.g., liquid gruel, small meatballs, blenderized slurries).
  • Many cases benefit from gastrostomy tube placement for feeding; however, this does not prevent gastroesophageal reflux and potential aspiration or aspiration of saliva.
  • Feeding and drinking should be from an elevated position (45–90° from floor) and the upright position should be maintained for 10–15 minutes after eating or drinking. An upright position may be easier to attain with the use of a specific “chair” (e.g., Bailey chair).

Client Education

  • Most cases of megaesophagus require life-long therapy. Even if an underlying etiology is found and treated, prognosis for resolution of megaesophagus is guarded. Client dedication is important for long-term management.
  • Most animals succumb to or are euthanized because of aspiration pneumonia or progression of underlying disease.

Surgical Considerations

  • Surgery is indicated for vascular ring anomalies, bronchoesophageal fistula, some foreign bodies and other obstructive lesions, or thymectomy.
  • Balloon dilation is indicated for cases of esophageal stricture.
  • Surgical resection of megaesophagus is not recommended.

Medications ⬆ ⬇

Medications

Drug(s)

  • Antibiotics for aspiration pneumonia (ideally based on culture and sensitivity from transtracheal wash or bronchoalveolar lavage).
  • Therapy for underlying etiology if indicated-immunosuppressives (use with caution if pneumonia present) for immune-mediated disease; pyridostigmine for MG, prednisone supplementation for hypoadrenocorticism
  • H2 blockers for esophagitis-ranitidine (1–2 mg/kg PO, IV q12h), famotidine (0.5–1 mg/kg PO, SC, IM, IV q12–24h). Proton pump inhibitors may be used in severe cases-omeprazole (1 mg/kg PO q24h) or pantoprazole (1 mg/kg IV q24h).

Prokinetics

  • The use of prokinetics in dogs and cats with diffuse megaesophagus is controversial and should be avoided because they will tighten the lower esophageal sphincter and possibly increase the risk of aspiration pneumonia. Prokinetics such as metoclopramide (1.0–2.0 mg/kg/day IV CRI or PO q6–8h) or cisapride (0.5 mg/kg PO q8–12h) are more effective for minimizing gastroesophageal reflux and esophagitis. Cisapride is more potent and effective than metoclopramide for increasing lower esophageal tone and enhancing gastric emptying, and can be used in animals with evidence of esophagitis but no evidence of megaesophagus, or in cats with esophageal dysmotility affecting the smooth muscle in the distal 1/3 of the esophagus.

Precautions

  • Absorption of orally administered drugs may be compromised.
  • Injectable forms should be used when applicable.
  • Immunosuppression, if indicated, must be used with caution due to risk of aspiration pneumonia.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Thoracic radiographs when aspiration pneumonia is suspected (fever, cough, lethargy).
  • Cases of pneumonia may require CBC, blood gas analysis, and bronchoalveolar lavage. Repeat thoracic radiographs in animals with congenital megaesophagus as spontaneous resolution may occur.
  • Examine and weigh patients regularly to evaluate disease progression and ensure adequate nutritional intake.

Prevention/Avoidance

If an esophageal foreign body is identified, remove as quickly as possible.

Possible Complications

  • Aspiration pneumonia
  • Others, depending on etiology

Expected Course and Prognosis

  • Congenital cases have a guarded prognosis (20–46% recovery).
  • Miniature schnauzers may have better prognosis.
  • Prognosis may be improved with identification and treatment of specific etiology (e.g., hypoadrenocorticism, vascular ring anomaly).
  • Roughly 50% cases of MG respond to therapy; however, megaesophagus may persist even if other signs of MG resolve.
  • Prognosis for idiopathic, adult onset disease is poor.
  • Owner dedication is crucial.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

Aspiration pneumonia

Age-Related Factors

  • Signs of regurgitation in very young animal or at weaning may indicate congenital lesion.
  • Prognosis may be better in young animals.

Zoonotic Potential

  • None for megaesophagus.
  • Rabies vaccination status should be determined in any animal with possible neurologic disease.

Synonyms

  • Esophageal aperistalsis
  • Esophageal dilatation

Abbreviations

  • ACTH = adrenocorticotropic hormone
  • ANA = antinuclear antibody
  • CNS = central nervous system
  • CSF = cerebrospinal fluid
  • CT = computed tomography
  • MG = myasthenia gravis
  • MRI = magnetic resonance imaging
  • SLE = systemic lupus erythematosus

Internet Resources

Authors Marguerite F. Knipe and Stanley L. Marks

Consulting Editor Stanley L. Marks

Client Education Handout Available Online

Suggested Reading

Mace S, Shelton GD, Eddlestone S. Megaesophagus. Compend Contin Educ Vet 2012, 34(2):E1.