What had puzzled the endocrinologist about our patient was that her thyroid hormone levels were high, but her TSH was normal. This pattern is seen in the syndrome of resistance to thyroid hormone, a rare condition in which the body is insensitive to cues regulating the thyroid hormone feedback loop. I went back and reviewed the literature on ADHD and thyroid hormone resistance. When thyroid hormone resistance was first described in 1967, doctors noticed that the children had enlarged thyroids. Later on, doctors noticed that the children sometimes seemed hyperactive and nervous, resembling children with ADHD. For a time, checking the thyroid function of children with a diagnosis of ADHD was sometimes done. Eventually, doctors noticed that children with thyroid hormone resistance were more prone to learning disabilities than children with ADHD. Some were also inattentive and hyperactive.
This adolescent girl’s picture was becoming even more confusing. She had symptoms that looked like ADHD, but she clearly did not have ADHD. She had a high thyroid hormone level that looked like Graves’ disease but didn’t have the low TSH level that went with it. Although her blood tests suggested that her body’s thyroid-TSH feedback system wasn’t working properly, she didn’t display the ADHD-like symptoms of hyperactivity and nervousness that are typical of thyroid hormone resistance.
After the girl and her mother left, I walked down the hall to the endocrinologist’s office. “Well, she doesn’t have ADHD,” I said. “And she doesn’t have the typical hyperactive symptoms that are described with thyroid hormone resistance. So I’m stumped.”
She smiled. “I was hoping you’d say that,” she said. “I don’t think she has thyroid hormone resistance. She’s got plain old Graves’ disease. She’s just hyperthyroid.”
“But what about the TSH?” I asked. “Shouldn’t that be low in Graves’ disease?”
“Yes, and that’s the tricky part. I was suspicious, because her symptoms didn’t fit the lab results, so I sent her blood to an academic lab in Chicago. They told me her TSH is actually very low. It turns out that she has an unusual antibody that reacts with the standard TSH test and gives a falsely high reading.”
“OK, but how does hyperthyroidism fit with her symptoms? I still can’t explain why she is so inattentive and disorganized.”
The endocrinologist then told me that in children and adolescents, the earliest indications of hyperthyroidism may be behavioral, like hyperactivity, nervousness, or moodiness. Forgetfulness and inattention—just like our patient’s symptoms—are common. That was something I hadn’t known, never having had a patient with early Graves’ disease, but it certainly made sense.
We started our patient on methimazole, a medication that decreases the production of thyroid hormone. Within a few months, she was back to earning straight A’s and finishing her homework in nothing flat. Her mother was thrilled. So was I.