Saturday, September 22, 2012

Megaesophagus and Hypothyroidism in Dogs

Reversible Megaesophagus Associated with
Primary Hypothyroidism in a Dog

By F. Fracassi and A. Tamborini

Hypothyroidism is frequently cited as a possible cause of megaesophagus in dogs (1-4). However, a definitive association between hypothyroidism and megaesophagus has not been proven. Based on the limited response to the appropriate thyroid hormone supplementation in most dogs, there has been little proof of a true causal relationship between hypothyroidism and megaesophagus (1-4).

In this case report by Fracassi and Tamborini (5), they describe a dog with well-documented hypothyroidism and concurrent megaesophagus. This dog responded very well to L-thyroxine replacement therapy, with complete resolution of all clinical signs of hypothyroidism, as well as the associated megaesophagus.

Case Report
A 7-year old female German shepherd dog presented for regurgitation shortly after feeding. On physical examination, the dog had a body condition score of 6/9 and a diffusely poor, dull and dry hair coat. There were areas of alopecia and hyperpigmentation in areas of friction, as well as on the tail.

Routine blood test results showed a moderate, non-regenerative normochromic and normocytic anemia, with mild hypercholesterolemia. Survey radiography of the thorax, before and after oral administration of barium, revealed that megaesophagus was present (Figure 1).

Chest x-ray of dog with hypothyroidism, showing megaesophagus
Serology for acetylcholinereceptor antibodies was negative; therefore, myasthenia gravis was considered unlikely.

Results of thyroid function testing showed a high concentration of serum cTSH (0.84 μg/L; reference range, 0.03-0.38 μg/L) together with low basal value for total T4 (6.4 nmol/L; reference range, 14-45 nmol/L). This combination of low T4 and high TSH values was consistent with primary hypothyroidism.

A recombinant human TSH stimulation test was also performed, by measuring the serum T4 concentration before and 6 hours after IV injection of 75 μg of rhTSH (6). Results of the TSH stimulation test showed low serum concentrations of both basal T4 and post-TSH T4, diagnostic for hypothyroidism. The final diagnosis was hypothyroidism associated with probable secondary megaesophagus.

Treatment was initiated with levothyroxine (20 μg/kg , BID). One week later, the owner reported that the dog was much more active, with no more regurgitation. At recheck 25 days later, the dog was found to be in a good condition; its hair coat was less dull and areas of new hair growth were apparent. Repeat chest radiographs showed resolution of the megaesophagus. The serum T4 value collected 4-hours post-pill was in the high-normal range (47.6 nmol/L) and considered adequate for replacement.

Two years after the diagnosis, the dog was clinically well on L-T4 replacement. No further dermatological signs or regurgitation have been reported.

My Bottom Line

The clinical signs of canine hypothyroidism can be vague and are frequently nonspecific (1-4). The most common presenting signs include lethargy, obesity or weight gain, and dermatologic signs (Figure 2). The metabolic features are often considered subtle, whereas dermatological changes more frequently prompt investigation of thyroid function.

Prevalence of clinical features of canine hypothyroidism
Is there really a true association between hypothyroidism and megaesophagus? This issue is quite controversial (3,4,7). In a case-controlled study of 136 dogs with acquired megaesophagus, 272 control dogs from the general hospital population and 151 control dogs that underwent a TSH response test, no association between hypothyroidism and megaesophagus was found (7).

Similarly, in another retrospective study of 29 hypothyroid dogs, 4 dogs had megaesophagus—although one dog showed an improvement of the clinical signs of regurgitation after L-T4 treatment, radiological evidence of megaesophagus persisted in all 4 the dogs (8). This suggests that there may not be any relationship between thyroid dysfunction and megaesophagus in these dogs.

However, there also have been a few well-documented cases of dogs with concurrent hypothyroidism and megaesophagus in which complete resolution of the clinical and radiographic signs were seen after L-T4 treatment (9). This suggests, as does this present case report, that at least some hypothyroid dogs with secondary megaesophagus will respond well to thyroid hormone replacement therapy with resolution of all esophageal signs.

Overall, megaesophagus, although a very rare signs of hypothyroidism, does appear to be associated with hypothyroidism in at least some dogs.

  1. Panciera DL. Hypothyroidism in dogs: 66 cases (1987-1992). J Am Vet Med Assoc 1994;204:761-767. 
  2. Dixon RM, Reid SW, Mooney CT. Epidemiological, clinical, haematological and biochemical characteristics of canine hypothyroidism. Vet Rec 1999;145:481-487. 
  3. Mooney CT. Canine hypothyroidism: a review of aetiology and diagnosis. N Z Vet J 2011;59:105-114. 
  4. Mooney CT, Shiel RE. Canine hypothyroidism In: Mooney CT,Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;63-85.
  5. Fracassi F, Tamborini A. Reversible megaoesophagus associated with primary hypothyroidism in a dog. Vet Rec 2011;168:329b. 
  6. Boretti FS, Sieber-Ruckstuhl NS, Wenger-Riggenbach B, et al. Comparison of 2 doses of recombinant human thyrotropin for thyroid function testing in healthy and suspected hypothyroid dogs. J Vet Intern Med 2009;23:856-861. 
  7. Gaynor AR, Shofer FS, Washabau RJ. Risk factors for acquired megaesophagus in dogs. J Am Vet Med Assoc 1997;211:1406-1412.  
  8. Jaggy A, Oliver JE, Ferguson DC, et al. Neurological manifestations of hypothyroidism: a retrospective study of 29 dogs. J Vet Intern Med 1994;8:328-336. 
  9. Huber E, Armbrust W, Forster JL, et al. Resolution of megaesophagus after treatment of concurrent hypothyroidism in a dog. Schweiz Arch Tierheilkd 2001;143:512-514.

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