| General Description |
In Bears
In an adult female grizzly bear (Ursus arctos - Brown bear)
- Rough coat, development of an ulcerated lesion on the snout,
development of generalised skin lesions (alopecia, moist
dermatitis)
by six months later, and lethargy and weight gain. (J4.157.w3)
- T3 uptake (measured in blood collected within 20 minutes of
euthanasia) was 21% (normal 40-60%).
In an adult female Ursus americanus - American black bear
- Lethargy, weight gain (obese), inappetance and patchy alopecia, with
hair shafts easily epilated. (J2.35.w1,
P1.2002.w5)
In two Ursus maritimus - Polar
bears (P1.1979.w3)
- Low T4 levels and reduced response to a TSH stimulation test was
noted in a female and a male polar bear with chronic ulcerative
dermatitis (female) and chronic ulcerative pododermatitis (male). (P1.1979.w3)
In Tremarctos ornatus - Spectacled
bear, with associated alopecia. (P77.1.w19)
Gross pathology
In an adult female grizzly bear (Ursus arctos - Brown bear)
- Skin:
- Bilaterally symmetrical alopecia.
- Over the neck and rump, thickening of the skin.
- Diffuse areas of moist dermatitis.
- Localised pyoderma.
- Thyroids:
- Enlarged, 8 x 5 x 3 cm, firm, with a rough, semi-lobulated
appearance. On the cut surface, translucent with cystic centres
containing 3-5 mL tenacious amber fluid.
- Liver:
- Diffuse areas telangiectasis.
- Gall bladder distended with bile.
(J4.157.w3)
In an adult female Ursus americanus - American black bear
- Thyroid: lobes enlarged. Right lobe 7.5 x 3.0 x 1.0 cm, with a cyst
on the cranial pole, 2.5 x 2.0 x 0.5 cm, containing 3 ml clear amber
fluid. Left lobe 6.5 x 3.5 x 1.0 cm; from the cut surface, which was
multilobulated, a small amount of thick yellow-brown opaque fluid
exuded. (J2.35.w1)
Histopathology
In an adult female grizzly bear (Ursus arctos - Brown bear)
- Skin:
- Epidermis thickened; acanthosis and hyperkeratosis
present.
- Areas of epidermal inflammation and ulceration into the dermis.
- In many hair follicles, hyperkeratosis and accumulation of
inflammatory cells, with either no hair shaft or broken hair.
- Thyroid:
- Enlarged thyroid follicles, with acini coalesced to form cysts,
some having ruptured with colloid escaping into the interstitial
spaces.
- Colloid was mainly weakly acidic.
- Epithelium of acini was flattened.
- In a few areas, hyperactive cells projecting into the
colloid space.
- Larger cysts had hyperplastic lining, 2-10 cells, thick.
- Liver:
- Multiple areas of telangectasis, with dilatation of the
sinusoidal capillaries.
(J4.157.w3)
In an adult female Ursus americanus - American black bear
- Thyroid: Colloid goitre of both lobes: follicles of both
lobes lined with flattened cuboidal epithelium and distended by
abundant intrafollicular eosinophilic colloid; limited amounts of
normal follicular architecture were remaining. In the right lobe, also
a follicular cystadenoma, lined by flattened cuboidal epithelial
cells, with focal areas of mild nuclear pleomorphism, replacing about
a third of the cranial pole of the lobe, and filled with homogenous
amphophilic colloid. (J2.35.w1)
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| Further Information |
Hypothyroidism in
an adult female grizzly bear (Ursus arctos - Brown bear)
may have been diet related. The bear was from an endemic goitre area of
Canada, and the diet may have been low in iodine and may have contained
some mild goitrigenic substances. (J4.157.w3)
Diagnosis
- History, clinical examination and results of thyroid activity tests.
(J4.157.w3)
- History, physical examination and endocrinological findings: low
total thyroxine (T4), 12.0 nmol/L, versus 17,8 +/- 4.5 nmol/L
for eight healthy conspecifics, and low fT4ED (free T4
by equilibrium dialysis), 9.0 pmol/L, versus 30.9 +/- 6.4 pmol/L for
eight healthy conspecifics. (J2.35.w1,
P1.2002.w5)
Treatment
- In two polar bears, treatment with L Thyroxine, 3 mg twice daily
(female) or 2 mg twice daily (male) resulted in an increase in serum
T4 levels but no improvement in skin lesions. (P1.1979.w3)
- In an adult female Ursus americanus - American black bear,
levothyroxine sodium, at 0.022 mg/kg orally twice daily initially,
resulting in clinical improvement (improved hair coat and appetite,
increased activity, weight loss) within 30 days. Serum T4
and fT4ED, measured six hours after dosing, were 96.0 nmol/L
and 65.0 pmol/L respectively (about four times and two times the upper
limits for the normal conspecifics), then reduced to 0.018 mg/kg
orally twice daily, to 240 days of therapy, then a further reduction
to 0.011 mg/kg orally twice daily. This continued until the bear
was euthanised with severe lameness associated with osteoarthritis of
the stifles, tarsi and lumbar spine. (J2.35.w1,
P1.2002.w5)
- In Tremarctos ornatus - Spectacled
bear, thyroid replacement [no further details available]. (P77.1.w19)
Prevention
- Ensure adequate iodine in the diet, avoid inclusion of goitrogens in
the diet. (J4.157.w3)
- Supplementation with vitamin A may be beneficial, since the
condition may prevent conversion of carotene to vitamin A. (J4.157.w3)
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