Desiccated thyroid in the management of hypothyroidism: Part II
Thomas Repas, DO, FACP, FACE, CDE
January 6, 2009 09:49 AM
Most board-certified endocrinologists avoid desiccated thyroid in the
management of hypothyroidism for additional reasons.
Desiccated thyroid preparations contain an approximately 4:1 ratio of thyroxine (T4)
to triiodothyronine (T3), whereas the normal human thyroid has of a ratio of 11:1. These
preparations result in supraphysiologic levels of T3 in the two to four hours after
ingestion. This is due to the rapid release of T3 from thyroglobulin and the
immediate almost complete absorption of T3.
In my own practice, I have seen numerous individuals referred to me on
desiccated thyroid with fully suppressed thyroid-stimulating hormone. This is because the dose was
titrated based on symptoms or clinical findings rather than biochemical assays.
Some have had anxiety, insomnia, tremulousness, heat intolerance and other
symptoms clearly due to iatrogenic hyperthyroidism. The long-term consequences
of hyperthyroidism are not benign. Nevertheless, many have absolutely refused
to allow me to decrease their dose, despite my concerns.
With hormone therapy, just as too little is unacceptable, too much is
also unacceptable. More is not always better.
Some alternative care practitioners claim that standardized laboratory
testing is unreliable. They use other methods to justify their approach such as
basal body temperature measurement, testing of tendon reflexes and how the
patient generally feels subjectively.
Although thyroid hormone certainly has effects on metabolism, in order
for there to be a consistently measurable increase in body temperature, many
patients must be rendered hyperthyroid. There are many other factors that
affect basal body temperature, not only the thyroid. In addition, there is
wide intra-individual variation in body temperature. Body temperature varies
depending on time of day and how it is measured. “Normal” body
temperature should not be defined as 98.6º F ± 0º, just
as we do not define “normal” TSH as exactly 1.00 mIU/L. Normal is a
range, not a single value. Using basal body temperature to modify the dose of
thyroid HT is imprecise and not supported by the
scientific evidence. It is the same with measurement of reflexes and other
non-specific clinical findings.
Regarding symptoms and the subjective
feeling of wellness, that is problematic. My goal is not only to prevent and
treat disease, but for all of my patients to feel better on whatever therapy we
have chosen. The problem here is that there are innumerable reasons to feel
poorly, often with identical symptoms to hypothyroidism, and yet not due to
Too many times have I seen other medical
diagnoses missed, because every symptom a patient had was attributed to their
thyroid and no further evaluation was done. It is easier and less time
consuming to write a prescription than it is to think, ask questions and most
important of all ... to listen.
Sometimes we need to tell patients what they need to hear, even if it is
not what they would like to hear. This should be done as kindly and tactfully
as possible, but it must be done nonetheless.
-To be continued-