Is a Thyroid Problem Causing My Fatigue?


Is a Thyroid Problem Causing My Fatigue?

Fatigue is definitely one of the symptoms of thyroid deficiency (hypothyroidism.) Thyroid hormones (T4, thyroxine and T3, triiodothyronine) regulate the metabolic processes and an insufficient amount of the hormone causes a generalized slowing of these processes, cold intolerance, weight gain, constipation, dry skin and other problems in addition to fatigue.

The best way to determine thyroid hormone deficiency is through measuring the thyroid stimulating hormone. Thyroid stimulating hormone (TSH) and thyroid hormone exist in a reciprocal relationship where a drop in the thyroid hormone level produces a rise in TSH which serves to stimulate the thyroid gland to make more thyroid hormone.

TSH is not the sole measure of thyroid status although it is often used as the solitary screen for hypothyroidism. In the event of a problem with the pituitary gland’s ability to regulate TSH an individual may have low thyroid hormone level in the setting of a low or normal TSH and the diagnosis of hypothyroidism might be missed.

Measuring thyroid hormone directly can uncover a situation as described above. In such a case thyroid hormone, measured as free T4, would be low indicating thyroid deficiency in the presence of a normal or low TSH.

Why not simply rely on a direct measurement of thyroid hormone (free T4) to screen for a hypothyroidism? A low free T4 almost always defines a low thyroid state but thyroid hormone is very precisely gauged to the individual where a particular free T4 level, although in the normal range, might be insufficient for a particular person. TSH when functioning correctly increases when the thyroid hormone drops below a specific set point even though that set point might be in the normal range for the general population.

Therefore, measuring TSH and free T4 can almost always correctly identify a hypothyroid condition. TSH alone can identify hypothyroidism 95% of the time which is why it is often used separately as a screen for thyroid disease.

However, there is a controversy about whether a normal TSH (usually 0.4 to 5.0 mU/L) is actually normal. The point of those who would reduce the TSH upper limit of normal to 2.5 mU/L is that an upper limit of 5.0 mU/L was extracted from a general population that included many people with thyroid disease thereby distorting the notion of normal. Using a population free of thyroid disease produces an upper limit of 2.5 mU/L.

To complicate matters further, TSH increases somewhat with age in the absence of anything to suggest a hypothyroid state. The upper limit of normal for patients in their eighties could be as high as 6 to 8.

There are additional tests used to define thyroid status including the T3-resin uptake and antithyroid peroxidase (anti-TPO.) The latter is usually abnormal in patients with hypothyroidism and can, if present, can predict that hypothyroidism will eventually develop.

Thyroid disease characterized by a TSH of 10 or less and a normal free T4 is termed “subclinical hypothyroidism” the treatment for which is controversial with some experts recommending no treatment and others recommending thyroid hormone supplementation.

Attempts to define symptoms have been unsuccessful although many patients have complaints suggesting hypothyroidism, including fatigue. Statistical analysis of symptoms cannot separate this group from those with normal thyroid function. Most physicians think that patients with a TSH that is less than 10, although it is in the abnormal range, do not have symptoms attributable to thyroid disease. However, I have seen patients in this category with fatigue who have definitely responded to thyroid hormone treatment.



Types of Fatigue

Over 100 years ago William Osler, the father of internal medicine, divided fatigue into three types. The first is the lassitude and malaise associated with systemic illness such as tuberculosis, cancer, rheumatoid arthritis, etc. The second is the weakness associated with muscle and nerve disorders resulting from ordinary exertion. The last is a painful weariness – the cause of which often eludes investigation.

These categories provide a useful framework in attempting to diagnose the cause of an individual’s fatigue. Duration further categorizes the symptom. Most patients with prolonged, unexplained fatigue have the third type of fatigue described by Osler, a painful weariness.

Fatigue that is less than one-month in duration is often due to a passing virus, stress, or other causes that are difficult to define. The relatively brief nature of the problem eliminates the need for an intense medical investigation, and, unless the problem becomes recurrent, it can be dismissed as one of life’s minor problems.

Persistent, significant fatigue, however, is not a minor problem. Even a loss of 10% of a person’s vigor removes enthusiasm and joy from the day’s tasks. Fatigue pulls down the mood and makes everything an effort. Approximately 15% of the general population suffers from chronic fatigue, unrelieved by rest, lacking an adequate medical explanation.

Approximately 25% of patients visiting a medical doctor complain of fatigue. Less than half will be explained by a medical illness.

Fatigue caused by medical conditions has certain characteristics. A serious medical problem will occasionally present itself as unexplained fatigue before other symptoms become apparent but, inevitably, other symptoms will appear. For instance, a person with pancreatic cancer may first notice fatigue before the appearance of abdominal pain and the other symptoms of cancer occur. Therefore, the longer fatigue persists without other symptoms, the less likely a serious medical condition will serve as the eventual explanation.

Fatigue caused by a medical problem has other characteristics as well. Usually patients with typical, diagnosable, medical problems note that their energy is highest in the morning and slowly winds down over the course of the day as if the store of vigor slowly depletes. A nap may recharge the person.

Fatigue that remains unexplained usually has different characteristics. Many times, a person has a bimodal curve of energy, worse in the morning, improving with the day, fading in the afternoon, and, finally, getting a second wind at night. A nap can actually worsen things. Additionally, sleeping a long time can produce an overslept sensation.

Patients with less serious medical problems can, in certain circumstances, have fatigue with the absence of other symptoms, as is the case with hypothyroidism. Patients with low thyroid may notice tiredness before the other symptoms appear. These include dry skin, constipation, cold intolerance, etc. Likewise, a patient with anemia can feel tired before noticing other symptoms such as pale skin or obvious blood loss.

Causes of fatigue are often easy to figure out. Usually a visit to the doctor and a standard panel of blood tests provides a definite answer. If, after a thorough exam and appropriate blood tests, no answer is apparent, it is unlikely that a medical explanation will be found.