A Rare Form of Hypothyroidism

Shehzad Basaria, MD, and Milena Braga, MD

Disclosures

South Med J. 2002;95(5) 

In This Article

Case Report

A 46-year-old woman was referred to the endocrine clinic for evaluation of suppressed thyrotropin level. The patient had been well until 4 months earlier, when she began to have fatigue and lethargy along with cold intolerance and dry skin. She denied any history of heat intolerance, weight loss, change in neck size, or eye or skin changes. Her primary physician obtained thyroid function tests, which yielded the following values: thyrotropin <0.05 mU/L (normal, 0.5 to 4.5 mU/L), thyroxine (T4) 6.0 µg/dL (4.5 to 11.5 µg/dL), triiodothyronine (T3) 1.00 ng/mL (0.8 to 2.0 ng/mL), free T4 index (FTI) 6.6 (4.5 to 11.5), and T4 uptake 1.1 (0.8 to 1.3). The patient was referred to our clinic for further workup.

The patient denied any history of headaches, peripheral vision changes, or head trauma. Her medical history included unipolar depression, which was under excellent control. Total abdominal hysterectomy and bilateral salpingo-oophorectomy had been done 4 years earlier because of uterine fibroids. She was not receiving hormone replacement therapy. There was a family history of hyperthyroidism in an aunt and a niece. She denied any addictions, and her medications included sertraline, trazodone, and clonazepam.

Physical examination revealed normal vital signs. Extraocular movements and the visual fields with direct confrontation were normal. The thyroid gland was normal in size, shape, and texture. Skin and hair were dry, and deep tendon reflexes were normal. Significant laboratory values were as follows: thyrotropin 0.11 mU/L, T3 0.74 ng/mL, T4 5.2 µg/dL, FTI 5.2, T4 uptake 1.0, free T4 0.5 ng/dL (0.7 to 1.6 ng/dL), cortisol 19.9 µg/dL, prolactin 6.9 ng/mL (normal, 0 to 18), corticotropin (ACTH) 21.7 pg/mL, luteinizing hormone (LH) 43.3 mIU/mL, follicle-stimulating hormone (FSH) 90.2 mIU/mL, and insulin-like growth factor I (IGF-I) 157 ng/mL. The serum cortisol level was measured at 8 AM. Magnetic resonance imaging (MRI) with gadolinium showed a normal pituitary gland with normal enhancement.

Since the patient's thyroid function tests were consistent with central hypothyroidism and all the other anterior pituitary hormones and MRI were normal, the possibility of isolated thyrotropin deficiency (secondary hypothyroidism) or thyrotropin-releasing hormone (TRH) deficiency (tertiary hypothyroidism) was entertained. To distinguish between these two distinct entities, TRH stimulation test was done. The results are shown in Table 1 .

The TRH test showed a blunted thyrotropin response suggesting secondary hypothyroidism (thyrotropin deficiency), and thyroxine replacement therapy was started. At 2-month follow-up, the patient had less cold intolerance, fatigue, and lethargy. Thyroid function values were thyrotropin 0.09 mU/L, T3 1.02 ng/mL, and free T4 1.0 ng/mL.

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