Thyroid function testing in elephant seals in health and disease.

Area of Science:

• Marine Mammal Health
• Veterinary Dermatology
• Endocrinology

Background:

• Northern Elephant Seal Skin Disease (NESSD) is a severe skin condition in yearling seals.
• NESSD is associated with decreased thyroid hormones (T4 and T3), mimicking hypothyroidism.
• Sick euthyroid syndrome, a condition where illness suppresses thyroid hormones in healthy glands, can mimic true hypothyroidism.

Purpose of the Study:

• To investigate the role of hypothyroidism in the etiology of Northern Elephant Seal Skin Disease (NESSD).
• To differentiate between true hypothyroidism and sick euthyroid syndrome in affected elephant seals.

Main Methods:

• Thyroid function was tested in stranded yearling elephant seals using TSH stimulation.
• Three groups were studied: healthy seals (N=9), seals with NESSD (N=16), and seals with other illnesses (N=10).
• Circulating thyroxine (T4) levels were measured before and after TSH administration.

Main Results:

• Thyroid Stimulating Hormone (TSH) administration significantly increased T4 levels in all three groups of elephant seals.
• This indicates that the thyroid glands in seals with NESSD are responsive and functioning normally.

Conclusions:

• Elephant seals with NESSD exhibit a "sick euthyroid" state, not true hypothyroidism.
• The thyroid gland is not the primary cause of Northern Elephant Seal Skin Disease.