Thyroid hyperplasia in
it be a window to goiter in humans?
Gerald L. Crow
Waikiki Aquarium, University of Hawaii
Wednesday, April 28, 1999
3:00 p.m.Pacific Forum
Thyroid hyperplasia (goiter) is a common clinical finding in both elasmobranchs and
human beings throughout the world. If left untreated, the thyroid gland can expand to
almost 300 times its normal size. Management of thyroid hyperplasia has typically been
centered on iodide or hormone replacementas an additive in water, an injection, or
an oral supplement.
The thyroid gland produces hormones (T4, T3) which help to regulate physiology. The
hormone T4 (thyroxine) is converted extrathyroidally to T3 (triiodothyronine). Goitered
elasmobranchs are hypothyroid and exhibit reduced concentrations of these hormones.
A review of captive elasmobranch thyroid hyperplasia cases from the Registry of Tumors
in Lower Animals reveals an interesting dichotomy. Cases of diffuse hyperplastic goiter
were found to have mostly small follicles with little to no colloida condition that
could be expected in iodine deficiency goiter. However, five additional cases were
characterized by an enlargement of follicles, filled with colloid. When left untreated in
humans, colloid goiters often progress to multinodular colloid goiters, and there is
reason to believe that this is also the case in elasmobranchs. Since colloid goiters are
more likely to occur in the presence of goitrogenic agent(s), water chemistry studies are
needed for the diagnosis of thyroid hyperplasia in elasmobranchs
In elasmobranch necropsy cases there is a striking similarity to goiter in humans.
Detailed studies are now underway to determine the timeline and morphological changes that
occur during goiter development. The findings may aid in our understanding of goiters in
fluorescence- From ecophysiology to biotechnology
Last updated: December 19, 2000