Persistently elevated TSH on high- dose levothyroxine therapy

I saw an elderly man with thyroid-stimulating hormone levels that have remained in the 20 mIU/L to 40 mIU/L range, despite being prescribed 200 mcg or more of levothyroxine per day. The patient swore he was taking the levothyroxine every day as prescribed. His primary care physician was at a loss so he sent the patient to me.

This is a situation in which taking a thorough history is essential. Lack of response to levothyroxine therapy occurs due to variety of reasons. Medications such as bile acid sequestrants, sucralfate and others can interfere with absorption, as can taking medication with food, dietary fiber, soy or nutritional supplements containing iron. Gastrointestinal malabsorption, such as from celiac sprue or short bowel syndrome, can decrease absorption of levothyroxine. Increased clearance may occur from phenobarbital, phenytoin, carbamazepine and rifampicin. Weight gain or pregnancy can increase demand.

The most common reason for lack of response to levothyroxine, however, is non-compliance with therapy. Most often this is due to patients simply forgetting to take doses, such as an elderly individual with mild dementia. Pillboxes and other reminders can be very helpful in this situation.

In others, there is resistance to taking medication or pill of any kind. The dichotomy of hypothyroid patients who are sent to me is interesting. Many patients who have high-normal or slightly high TSH are asking for dose increase because of intolerable symptoms, which we oblige. There are a few, however, who refuse to take anything at all, even after I explain to them how much better they would feel. It amazes me that they would prefer to suffer with untreated hypothyroidism, even with a TSH of ≥40 mIU/L.

After tactfully asking this gentleman again if he was taking as prescribed, he confessed to skipping doses because he could not afford his prescription. We provided him with all the samples we had of his dose and will be retesting TSH in several weeks. Thyroid hormone replacement therapy is not costly compared to other prescription medications. However, it does not matter how inexpensive a medication is, if you cannot afford it then you cannot take it.