Megaesophagus

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Congenital megaesophagus due to persistent right aortic arch[1]
Idiopathic megaesophagus in a dog[1]
Lateral thoracic radiographs demonstrating megaesophagus (arrows) and an asymmetric alveolar lung pattern affecting the left caudal and right middle lung lobes consistent with aspiration pneumonia[2]

Megaesophagus is a persistent, enlarged canine esophagus.

This disorder may be congenital (such as certain breeds, and secondary to persistent aortic arch) or acquired, and can range from mild to severe dilation. Secondary megaesophagus can be caused by any disease that results in inhibited esophageal peristalsis by either mechanical or neurological dysfunction.

Depending on the severity of esophageal obstruction/paralysis, some dogs can eat soft foods regularly, with few clinical signs while others are unable to drink even water and chronically regurgitate despite a good appetite.

Lesions and obstruction can be located anywhere from the upper esophageal sphincter to the lower esophageal sphincter.

Myasthenia gravis is the most common cause of acquired megaesophagus in dogs.

Other causes include:

  • Genetic
- Autosomal recessive in Miniature Schnauzer, Golden Retriever, German Shepherd[3], Great Dane, New Foundland, Shar Pei - clinical signs appear from 3 months of age
  • CNS neuropathy
- Canine distemper virus
- cervical vertebral instability
- Fibrinoid leukodystrophy[4] - French Bulldog
- brainstem lesions (e.g. empty sella syndrome[5], trauma, neoplasia)
  • Peripheral neuropathy
- Polyneuropathy[6], polyradiculoneuritis, ganglioradiculitis, dysautonomia[7], laryngeal paralysis, vagal nerve dysfunction[8]
- Tetanus
- Botulism
- Spirocerca lupi
- Trypanosoma spp
- Neopsora caninum - secondary esophageal myositis[11]
- Hypothyroidism
- Hypoadrenocorticism - due to impaired muscle activity
- Systemic lupus erythematosus
- Polymyositis
- Dermatomyositis
- Golden Retriever Muscular Dystrophy[13]
- Masticatory muscle myositis
- Gangliosidosis
  • Mechanical obstruction
- hiatus hernia[14]
- Cricopharyngeal achalasia[15] (upper esophageal sphincter neuropathy), often associated with hypothyroidism[16]
- Persistent left and/or right aortic arch[17] or left cranial vena cava[18]
- Pyloric stenosis
- Thymoma[19]

Clinical symptoms are frequent repetitive regurgitation of undigested food, dysphagia, ptyalism, halitosis, reluctance to eat in spite of appetite, coughing (associated with aspiration pneumonia) and weight loss. Swelling of the ventral neck near the thoracic inlet is sometimes seen, particularly in young dogs.

Abnormal esophageal motility can exist without megaesophagus, and esophageal dysmotility without overt megaesophagus exists in both symptomatic and asymptomatic young dogs (often 4 - 9 months of age). Motility in these cases can improve with age suggesting a delayed maturation of esophageal musculature[20].

Diagnosis is based on identification of a dilated or hypomotile esophagus on barium meal radiographs, or the presence of a distended esophagus containing food or foreign objects. 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[21].

Associated aspiration pneumonia may be observed on radiographic imaging.

Esophageal motility can be assessed with fluoroscopic, manometric or scintigraphic procedures, which may assist determining whether the condition is primary or secondary. Most dogs with idiopathic megaesophagus have a very large, dilated, aperistaltic esophagus, whereas secondary megaesophagus shows faster transit times. Esophagostomy via endoscopy is not usually helpful in determining a cause, but can eliminate other causes such as foreign bodies, parasites, neoplasia, etc.

A differential diagnosis would include Spirocerca lupi infection, hiatal hernia, diaphragmatic hernia or gastroesophageal intussusception[22].

In secondary megaesophagus, treatment involves addressing primary disease states.

Although there is no specific treatment of megaesophagus, use of special feeding diets and raised bowl is the primary method of maintaining well-being in non-critical patients. The use of an esophageal stent may be required to be placed if cricopharyngeal achalasia or severe esophageal cicatrization is a underlying complication[23].

Antimicrobial therapy is important if secondary aspiration pneumonia is involved. Prokinetic drugs (e.g. cisapride, metoclopramide) have variable responses in long-term treatment of this condition.

Long-term complications include esophageal scarring, esophageal necrosis, necrotizing sialometaplasia[24], persistent severe megaesophagus and, in rare cases, hypertrophic osteoarthropathy[25].

References

  1. 1.0 1.1 4Shared
  2. Richardson D (2011) Acquired myasthenia gravis in a poodle. Can Vet J 52(2):169-172
  3. Tsai KL et al (2012) Genome-wide association studies for multiple diseases of the German Shepherd Dog. Mamm Genome 23(1-2):203-211
  4. Ito T et al (2010) Fibrinoid leukodystrophy (Alexander's disease-like disorder) in a young adult French bulldog. J Vet Med Sci 72(10):1387-1390
  5. Burgener IA et al (2007) Empty sella syndrome, hyperadrenocorticism and megaoesophagus in a dachshund. J Small Anim Pract 48(10):584-587
  6. Gabriel A et al (2006) Laryngeal paralysis-polyneuropathy complex in young related Pyrenean mountain dogs. J Small Anim Pract 47(3):144-149
  7. Gajanayake I et al (2008) Autoimmune myasthenia gravis and dysautonomia in a dog. J Small Anim Pract 49(11):593-595
  8. Holland CT et al (2002) Selective vagal afferent dysfunction in dogs with congenital idiopathic megaoesophagus. Auton Neurosci 99(1):18-23
  9. Puschner B et al (2012) Thallium toxicosis in a dog consequent to ingestion of Mycoplasma agar plates. J Vet Diagn Invest 24(1):227-230
  10. Hopper K et al (2001) Megaoesophagus in adult dogs secondary to Australian tiger snake envenomation. Aust Vet J 79(10):672-675
  11. Basso W et al (2005) Confirmed clinical Neospora caninum infection in a boxer puppy from Argentina. Vet Parasitol 131(3-4):299-303
  12. Arnell K et al (2012) Persistent Regurgitation in Four Dogs with Caudal Esophageal Neoplasia. J Am Anim Hosp Assoc Nov 12
  13. Bedu AS et al (2012) Age-related thoracic radiographic changes in golden and labrador retriever muscular dystrophy. Vet Radiol Ultrasound 53(5):492-500
  14. Kirkby KA et al (2005) Paraoesophageal hiatal hernia and megaoesophagus in a three-week-old Alaskan malamute. J Small Anim Pract 46(8):402-405
  15. Elliott RC (2010) An anatomical and clinical review of cricopharyngeal achalasia in the dog. J S Afr Vet Assoc 81(2):75-79
  16. Bruchim Y et al (2005) L-thyroxine responsive cricopharyngeal achalasia associated with hypothyroidism in a dog. J Small Anim Pract 46(11):553-554
  17. Loughin CA & Marino DJ (2008) Delayed primary surgical treatment in a dog with a persistent right aortic arch. J Am Anim Hosp Assoc 44(5):258-261
  18. Larcher T et al (2006) Persistent left cranial vena cava causing oesophageal obstruction and consequent megaoesophagus in a dog. J Comp Pathol 135(2-3):150-152
  19. Uchida K et al (2002) Thymoma and multiple thymic cysts in a dog with acquired myasthenia gravis. J Vet Med Sci 64(7):637-640
  20. Bexfield NH et al (2006) Esophageal dysmotility in young dogs. J Vet Intern Med 20(6):1314-1318
  21. Wray JD & Sparkes AH (2006) Use of radiographic measurements in distinguishing myasthenia gravis from other causes of canine megaoesophagus. J Small Anim Pract 47(5):256-263
  22. McGill SE et al (2009) Nonsurgical treatment of gastroesophageal intussusception in a puppy. J Am Anim Hosp Assoc 45(4):185-190
  23. Zhu YQ et al (2010) Temporary self-expanding cardia stents for the treatment of achalasia: an experimental study in dogs. Neurogastroenterol Motil 22(11):1240-1247
  24. Schroeder H & Berry WL (1998) Salivary gland necrosis in dogs: a retrospective study of 19 cases. J Small Anim Pract 39(3):121-125
  25. Watrous BJ & Blumenfeld B (2002) Congenital megaesophagus with hypertrophic osteopathy in a 6-year-old dog. Vet Radiol Ultrasound 43(6):545-549