A 36-year-old woman with a past medical history of fibromyalgia presented to her general physician for a regular check-up. The patient reported that her mother was recently diagnosed with hypothyroidism and requested that her scheduled blood work include thyroid function…

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A 36-year-old woman
with a past medical history of fibromyalgia presented to her general physician
for a regular check-up. The patient reported that her mother was recently
diagnosed with hypothyroidism and requested that her scheduled blood work include
thyroid function tests. The patient said she has been well; even her symptoms
related to fibromyalgia had been under control. Her only complaint was some
hair loss, but it had slightly improved since she began using over-the-counter
supplements 3 months before her appointment.

On physical
examination, the patient appeared to be healthy: her vital signs were normal,
there was no evidence of thyroid eye disease, tremor, or tachycardia; and her
thyroid gland was not enlarged. Blood work completed the same day revealed
normal complete blood count and liver and kidney function tests, but
thyroid-stimulating hormone (TSH) was low, measuring 0.02 µIU/mL (reference
range, 0.4-4.6 mIU/L). Free thyroxine (T4) was measured at 24 pmol/L (reference
range, 10-19 pmol/L), and free triiodothyronine was measured at 7.1 pmol/L
(reference range, 3.5-6.5 pmol/L). After review of her previous laboratory
tests, it was found that her thyroid function tests, including TSH and free T4
levels, were previously normal on several occasions.

In a follow-up
visit, the patient denied recent pregnancy, iodine exposure, neck pain or
fever, recent acute illness, and symptoms of thyrotoxicosis. In addition, she denied
receiving any new medication, specifically amiodarone or lithium.