THYROID HORMONE RESISTANCE IN WOMEN

Janet, 40, had been healthy until she suffered a case of viral encephalitis 6 years prior to seeing me. During her hospitalization, her thyroid hormone levels (which control metabolism) were found to be normal. Over the next few months, however, she gained 40 pounds and developed swelling of her hands, feet and face. Her thyroid gland began enlarging and she was treated with thyroid hormone, which had no effect.

Later that year, she gained 23 more pounds, her hair became brittle and her cholesterol level became quite elevated. Tests of her thyroid function were again normal. Doctors progressively raised her dose of thyroid hormone, again without much benefit. A year ago, an endocrinologist evaluated her and stopped all thyroid medication. After this, her hair "stopped growing," her skin hardened, and she became depressed and forgetful.

She was put on Cytomel, a drug 10 times more potent than regular thyroid hormone. At a dose of 125 mcg per day, she began feeling better, her skin and hair improved, and she lost 20 pounds over two months. Unfortunately, her heart rate increased to 125 beats per minute. Alarmed, she stopped the Cytomel and all of her symptoms returned with a vengeance. Back on 100 mcg of Cytomel – yet still suffering from extreme fatigue, concentration problems, constipation, shortness of breath, excess sweating and weight gain – she was referred to me for an evaluation.

Tests indicated Janet had normal thyroid function, but she exhibited various symptoms of hypothyroidism (low thyroid function). While regular thyroid hormone treatment had been ineffective in treating these symptoms, Cytomel had reduced them. Unlike regular thyroid hormone, Cytomel had also suppressed her pituitary gland's thyroid stimulating hormone (TSH) level, indicating her pituitary was sensitive to the more potent thyroid hormone. (TSH levels go down when the pituitary thinks there is enough thyroid hormone in the blood and therefore no need to stimulate production of any more.)

After careful analysis, I suspected partial peripheral resistance to thyroid hormone syndrome. Blood test measurements confirmed that Janet was in a general hypothyroid state, with the exception of her heart, which was racing in a hyperthyroid state (excess thyroid function). She was treated with Cytomel in increasing doses, while a beta-blocker was used to lower her heart rate in consultation with her cardiologist.

While the benefits from the Cytomel would last for a few weeks or months, it would ultimately lose its effectiveness until the dosage was raised. Janet began feeling better for good on a dose of Cytomel that was nearly 10 times the normal dose for her size and weight – and a maximum dose of the beta-blocker. She returned two years later boasting that she was "svelte" again at 150 pounds. Her mood was good and she was gainfully employed. Her memory, cholesterol, skin and hair were all normal. She has remained on the Cytomel ever since and has had a stable, normal thyroid state.

Of the three known subtypes of thyroid resistance, two are easily detected. The third type – partial peripheral resistance to thyroid hormone syndrome, which Janet had – is harder to recognize. It’s often missed for years while doctors misdiagnose the patient as being depressed or having chronic fatigue. In this case, the pituitary puts out normal amounts of TSH. This leads the thyroid gland to make a normal, but completely ineffectual, amount of thyroid hormone that cannot function in the body. The patient is thus hypothyroid in a clinical sense. Fortunately, the thyroid gland's resistance can be overridden with sky-high levels of thyroid hormone in the form of Cytomel.

One interesting caveat: different organ systems can become more or less resistant over time, causing certain hyperthyroid symptoms to arise, thus necessitating close observation and response. An example was Janet's rapid heart rate and sweating on the Cytomel.