Discussion:
Thyrotoxicosis factitia is the term used to describe hyperthyroidism due
to excessive intake of exogenous thyroxine, it can be intentional for
therapeutic suppression of TSH in cases of thyroid malignancy and in
some cases to treat obesity [3], or inadvertent due to contamination
of supplements Like weight reducing supplements which claimed to be
herbal but contained an appreciable amount of both T3 and T4 or animal
thyroid tissue [4].
It is also seen in individuals with a background of underlying
psychiatric disease, for cosmetic reasons or accidental ingestion of
high quantity of thyroid hormones, most often seen in paramedical
personnel who have access to thyroid hormone or in patients for whom
thyroid hormone medication has been prescribed in the past [5].
The diagnosis of factitial hyperthyroidism in the absence of preexisting
disease of the thyroid is certain when there are typical thyrotoxic
manifestations like abdominal cramps, diarrhea, weight loss, heat
intolerance, together with thyroid atrophy and hypofunction which is
evidenced by the subnormal values of RAIU. Infiltrative ophthalmopathy
is never a feature but the eye signs are obvious. Serum TSH levels are
suppressed and serum T4 is high in most of the cases unless the patient
is taking T3, in such situation the T4 might be subnormal. Serum T3
concentrations is high in either case. Unlike true thyrotoxicosis the
presence of low, rather than elevated, values of serum thyroglobulin
(Tg) is a clear indication that the thyrotoxicosis results from
exogenous hormone and not from thyroid hyperfunction.
Other clinical complications commonly include skeleton system
(osteoporosis) and the cardiovascular system (tachyarrhythmias mainly
atrial fibrillation) which are the major target tissues adversely
affected by chronic use of exogenous thyroxine, however, abnormalities
in other systems have been reported.
A patient taking excessive amounts of levothyroxine and concealing this
from her doctors can pose a difficult diagnostic problem.
In terms of published literature, Braustein et al reported five cases of
unintentional thyrotoxicosis factitia where all of them ingested
levothyroxine pills as they believed that this hormone is non-toxic
substance that would help them to lose weight [6].
Hamburger Thyrotoxicosis was a rare form of exogenous thyrotoxicosis
which resulted when the grounded beef contained thyroid tissue. This
condition disappeared when there was a change in slaughtering practices.
The possibility of such a condition needs to be considered in the event
of an epidemic exogenous thyrotoxicosis [7].
In general thyrotoxicosis factitia
is thought to be caused by the secret ingestion of excessive amount of
thyroxine by neuropsychiatric patients [2]. The diagnosis of
thyrotoxicosis factitia depends on careful history to determine the use
of exogenous thyroxine or dietary supplements, a detailed examination to
exclude goiter and exophthalmos, thyroid image with normal ultra-sound
and low thyroid iodine uptake and laboratory findings with suppressed
TSH, high FT4 and FT3, with negative thyroid receptor antibody and low
thyroglobulin [8].
In our case since the patient was referred for control of
hyperthyroidism from gynecology unit as patient was supposed to go for
elective resection of multiple uterine fibroids. With detailed history,
careful reviewing of patient previous files and labs along with focused
clinical examination, there was a high index of clinical suspicion about
the exogenous use of levothyroxine and there were missing investigations
like ultrasound thyroid and thyroglobulin levels. Since the patient was
diagnosed as hyperthyroidism five years ago with suppressed TSH on
carbimazole maximum dose at present and still her TSH was suppressed
along with missing investigations. Given the patients inclination
towards cosmetic looks, leading question were put to the patient about
the use of any weight reducing medications, and to our surprise she was
taking herbal medications for weight loss with levothyroxine as one of
its content. We report this case as it was misdiagnosed as
thyrotoxicosis for five years and initiated on carbimazole, This
case highlights the importance of detailed history taking & medication
reconciliation which is vital in such a diagnostic dilemma.