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.