Primary Hypothyroidism in a Dog
By F. Fracassi and A. Tamborini
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.
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|
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|
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.
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