At a Glance

Factitious thyrotoxicosis may result from accidental, iatrogenic, or surreptitious ingestion of thyroid hormones, enough to cause symptoms of hyperthyroidism. It usually refers to the intentional ingestion of levothyroxine (T4) tablets, accidentally following ingestion of bovine thyroid extract in ground beef (T4 and T3), or, rarely, ingestion of T3 tablets in countries in which they are available in the pharmacopoeia.

Factitious thyrotoxicosis is more common in females.

A case report describes the occurrence of factitious hyperthyroidism following mesotherapy. Mesotherapy or dermatoliposclerosis is a technique used in Europe and South America for a variety of vascular and lymphatic disorders, as well as a method for reducing fat and local cellulite without liposuction. The technique involves the subcutaneous injection of poorly defined lipolytic formulations, some of which contain thyroid hormones. Another case report describes factitious hyperthyroidism via the ingestion of herbal supplements, some of which could be contaminated with thyroxine.

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Patients present with symptoms of hyperthyroidism (typically tachycardia, fever, anxiety, palpitations, hyperhidrosis, etc.) in the absence of an enlarged thyroid gland. Laboratory findings are characterized by an elevated T4, FT4, and low TSH, but these are confounded by the unexpectedly low radioactive iodine uptake (RAIU) or reduced glandular activity on the Tc-99m scan.

What tests should I request to confirm my clinical Dx? In addition, what follow-up tests might be useful?

Apart from the typical tests used to diagnose factitious hyperthyroidism (i.e., elevated T4, FT4, T3 and a low TSH, low RAIU), thyroglobulin levels should be obtained along with anti-thyroglobulin antibodies. Low serum thyroglobulin is very typical of factitious hyperthyroidism. Antithyroglobulin antibodies are typically absent. Thyroglobulin levels are raised in Grave’s disease, thyrotoxic adenoma, and toxic multinodular goiter (conditions with thyroid autonomy). In most cases, T4, FT4, and T3 are all elevated, since T4 converts to T3. When factitious hyperthyroidism is caused by exogenous ingestion of T3, T3 levels are elevated but T4 and FT4 are normal or low. (Table 1)

Table 1.
TSH FT4 Thyroglobulin
low high low

The main differential diagnosis are conditions associated with a low RAIU, such as subacute thyroiditis (usually associated with a tender painful thyroid) and silent thyroiditis (painless thyroid). Rarer forms of hyperthyroidism due to extrathyroidal production of thyroid hormones in conditions, such as hyperfunctioning thyroid metastasis and struma ovarii, require whole body scanning techniques. Hyperthyroidism due to excess ingestion of iodide can be excluded by a normal urinary excretion of iodine.

Are There Any Factors That Might Affect The Lab Results?

It is important to exclude the presence of anti-thyroglobulin antibodies because these can interfere in the immunoassay for thyroglobulin and produce falsely low thyroglobulin levels.

What Lab Results Are Absolutely Confirmatory?

Elevated T4, T3, and FT4 and low TSH and low or absent thyroglobulin, along with a low RAIU, is diagnostic.

Additional issues of clinical importance

The diagnosis of factitious thyrotoxicosis challenges the clinician’s acumen. The clinician must remain alert to possibility of accidental or surreptitious ingestion of thyroid. Symptoms associated with taking a lot of thyroxine can be variable. Children show symptoms, such as tachycardia, fever, nausea, seizure, diarrhea and irritability, and fatalities can occur. In adults, tachyarrhythmia, heart failure, myocardial infarction, stroke, psychosis and even death have been reported. Normalization of serum thyroid hormone levels and RAIU are associated with return of thyroglobulin and serum TSH to the normal range.

Error in test selection and interpretation

Although, traditionally, RAIU studies have been popular, scintigraphy with Tc-99, (technetium-99m pertechnetate) is more common and preferred for two reasons. First, Tc-99m can be given in higher doses, and, thus, the required number of scans can be accomplished quickly. This is also more patient friendly, since it does not require the patient to keep the neck extended for prolonged periods. Second, Tc-99m is more readily available, whereas I-123 is produced in a cyclotron facility and can be more complex to obtain.

Thyroid pain, tenderness of neck, raised erythrocyte sedimentation rate (ESR), and leukocytosis are not usually associated with factitious thyrotoxicosis.