Thyroid for Dummies (23 page)

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Preventing Harmful Drug Interactions

With so many drugs having an effect on thyroid function in one way or another, avoiding drug interactions becomes very difficult, particularly if one of the drugs you’re taking is thyroid hormone. If you’re taking thyroid hormone, your body isn’t able to make the subtle changes in thyroid function necessary to compensate for the other drug you’re taking, which is most likely reducing the thyroid hormone available to your systems. The best solution is to ask your pharmacist to check for interactions between the drugs you are taking, and your thyroid function.

Discovering Whether You’re at Risk

The drugs named in this chapter are given as their generic names. The generic name is the official name of the drug regardless of the name the manufacturer gives it, as all general practitioners (GPs) are encouraged to prescribe drugs generically for cost purposes.

This section groups the drugs according to their usage. If you have a specific medical problem – for example, diabetes – go to that section, look at the drugs listed there, and see whether the generic drug is the same as the one you’re using.

If one of the drugs listed here is something you take, ask your doctor if you need a thyroid function test:

ߜ Anaemia drugs, such as ferrous sulphate

ߜ Anti-addiction agents, such as methadone

ߜ Antibiotics, including:

• Ketoconazole

• Sulfonamide drugs: co-trimoxazole, sulfadiazine

• Rifampicin

ߜ Anti-inflammatory drugs, such as:

• Corticosteroid tablets: prednisolone, betamethasone, cortisone acetate, deflazacort, dexamethasone, hydrocortisone, methyl-prednisolone

• Aspirin

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ߜ Antithyroid drugs:

• Propylthiouracil

• Carbimazole

ߜ Drugs that suppress growth hormone, such as octreotide ߜ Nausea control drugs, such as:

• Domperidone

• Metoclopramide

• Prolactin control drugs, such as Bromocriptine

ߜ Diabetes drugs, including:

• Tolbutamide

• Chlorpropamide

ߜ Diuretics (drugs that reduce body water):

• Furosemide

ߜ Fat-lowering drugs:

• Colestyramine

• Colestipol

ߜ Heart rhythm drugs:

• Amiodarone

• Propranolol

• Phentolamine

ߜ Hormone replacements:

• Oestrogens (female hormones): found in the combined oral contraceptive pill, and in hormone replacement therapy

• Androgens (male hormones): testosterone

• Growth hormone

• Clomiphene

• Thyroid hormones: thyroxine sodium (T4), levothyroxine sodium (T4), liothyronine sodium (T3)

ߜ Pain medication:

• Morphine

• Diamorphine

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ߜ Peptic ulcer drugs:

• Aluminium hydroxide

• Sucralfate

• Cimetidine

• Ranitidine

ߜ Psychoactive drugs:

• Lithium

• Perphenazine

• Chlorpromazine

• Haloperidol

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Chapter 11

Spotting Thyroid Infections

and Inflammation

In This Chapter

ᮣ Encountering subacute thyroiditis

ᮣ Dealing with postpartum and silent thyroiditis

ᮣ Suffering from acute thyroiditis

ᮣ Finding out about a rare form of thyroiditis

The term
thyroiditis
is used in this book (check out Chapter 5) to mean the most common form of apparent inflammation of the thyroid, autoimmune thyroiditis – also known as Hashimoto’s thyroiditis and chronic thyroiditis.

This chapter also introduces you to causes of thyroiditis that are less common than autoimmune disorders but just as important to know about. Usually, but not always, thyroiditis is associated with infection.

Fortunately, infection of the thyroid is rare, perhaps because of all the anti-septic iodine and hydrogen peroxide found within the thyroid gland. Despite all this natural protection, every so often people develop an infected thyroid. In this chapter, you discover how doctors tell one form of infection from another, as well as the method of treatment and the prognosis for each illness.

Putting a Face on Subacute Thyroiditis

Joan is a 40-year-old woman who is suffering from a cough and cold with a low-grade fever for more than a week. One morning, she wakes to notice that her neck hurts. She can tell that the pain is located in the centre of her neck beneath her Adam’s apple. She goes to her doctor, who notes that her thyroid is enlarged and tender. The doctor also finds that Joan is nervous, and her fingers are shaking slightly.

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Her GP sends Joan for a thyroid function test, which shows that her free T4 is elevated while her TSH is depressed (refer to Chapter 4), suggesting hyperthyroidism. The doctor also requests a test for inflammation called an
erythrocyte sedimentation rate (ESR)
and the result is elevated. Knowing that neck pain is unusual in hyperthyroidism due to Grave’s disease (find out more in Chapter 6), the GP phones the thyroid specialist clinic who has a free appointment to see Joan the next day.

At the clinic, blood is taken to measure Joan’s serum thyroglobulin level, which comes back high, while the uptake of radioactive iodine is low (refer to Chapter 4). Joan finds out that she has subacute thyroiditis. She is started on aspirin and rapidly improves. The swelling of her neck declines, and the tenderness rapidly decreases.

Causes and effects

Subacute thyroiditis has many names including De Quervain’s thyroiditis, giant cell thyroiditis, and subacute painful thyroiditis. The condition is called
subacute
to differentiate it from a similar condition,
acute thyroiditis
, which is usually much more painful and associated with more symptoms that make the person sick.

Subacute thyroiditis is not very common, and typically accounts for less than 10 per cent of all cases of thyrotoxicosis.

As you see from Joan’s case, this condition often begins with an infection that suggests a virus. The person may have muscle aches and fever, and then begins to feel neck pain in the area of the thyroid. This pain is sometimes severe and usually brings the person to their doctor. When the doctor examines the patient, the thyroid is not only painful but enlarged as well.

Evidence exists that subacute thyroiditis is due to a virus: Cases of this condition are often seasonal, and they sometimes occur in outbreaks like any infectious disease. Over the years, doctors looking for a particular virus that might cause all cases of subacute thyroiditis have had little luck. The only virus that is found with some frequency is the mumps virus.

Subacute thyroiditis seems to occur more often in people with low immunity from an infection, such as AIDS (acquired immune deficiency syndrome), or people who receive bone marrow transplants for leukaemia.

As a result of the inflammation, the thyroid releases much of its stored hormone along with the stored thyroglobulin (refer to Chapter 4), resulting in hyperthyroidism. The virus also seems to temporarily damage thyroid cells 17_031727 ch11.qxp 9/6/06 10:45 PM Page 125

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and, as production of thyroid hormone isn’t ongoing, the hyperthyroidism lasts only a brief time, sometimes only a few days, until the thyroid gland is depleted of hormone. The person then goes through a brief period of normal thyroid function as hormone levels fall, before swinging into the opposite condition, hypothyroidism. Finally, because a viral illness usually doesn’t last, the thyroid gland returns to normal, the pain goes away, and the thyroid function returns to normal.

Like most thyroid conditions, subacute thyroiditis is more common in women than men; the ratio of cases is 3 to 1. This condition appears to have some genetic basis because the same genetic marker – an antigen on human white blood cells – is found in about 75 per cent of cases, suggesting that people who inherit this marker are more susceptible to the disease. In fact, two different genetic markers have been described. Interestingly, each one is associated with the disease occurring at a different time of the year, although in either case it generally occurs in the fourth or fifth decade of life.

A small (about 2 per cent) but definite possibility of a recurrence is likely some years later. This recurrence is generally milder than the original attack, although occasionally, someone may experience repeated attacks of pain.

Thyroid hormone helps to prevent such recurrences, but if recurrences keep coming back, removing the thyroid with surgery or radioactive iodine is necessary.

Laboratory findings

Lab tests are very helpful in pinning down a diagnosis of subacute thyroiditis.

Some of the findings are as follows:

ߜ The erythrocyte sedimentation rate (ESR), a general blood test for inflammation, is often unusually high considering the relative mildness of the symptoms.

ߜ Shortly after the thyroid becomes infected, up to 50 per cent of people experience hyperthyroidism, so TSH levels are low while FT4 levels are elevated.

ߜ Inflammation causes the release of a large quantity of both T4 and T3.

Because the thyroid contains so much more T4 relative to T3, compared to the blood, a drop in the ratio of T4 to T3 is experienced as they escape into the blood stream.

ߜ If liver tests are done, the level of alkaline phosphatase is often elevated.

It appears that the infection affects the liver in addition to the thyroid, though the impact on the liver is mild.

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ߜ Blood tests show that a lot of thyroglobulin is present in the blood.

ߜ The test for thyroid autoantibodies (refer to Chapter 4) is negative.

ߜ Some specialists suggest that a thyroid ultrasound study (refer to Chapter 4) is distinctive in subacute thyroiditis, but this test is not usually done.

ߜ The key test, the thyroid uptake of radioactive iodine, is very low, which differentiates this condition from other causes of hyperthyroidism.

When the results of all these tests and the clinical picture are put together, the diagnosis is fairly certain; although no one test proves that subacute thyroiditis is present. To prove the diagnosis, a biopsy of the gland is necessary, but the mildness of the disease means that a biopsy is rarely done.

Subacute thyroiditis differs from other forms of thyroiditis as it causes generalised thyroid pain, though sometimes the pain occurs on one side of the thyroid only. Another cause of a painful thyroid is bleeding, producing a haemorrhagic thyroid cyst. This pain usually occurs on one side of the thyroid and is not associated with a viral illness. Lab tests help to secure a diagnosis, particularly a radioactive uptake, which is normal for the cystic thyroid but low for subacute thyroiditis. In rare cases, chronic thyroiditis is painful (refer to Chapter 5). With chronic thyroiditis, levels of thyroid autoantibodies are high.

Treatment options

At the beginning of subacute thyroiditis, when someone is hyperthyroid, a drug such as propranolol is sometimes used to reverse the symptoms of excessive thyroid hormone. (Propranolol is a beta-blocker that slows the heart, decreases anxiety, and reduces tremor.) Antithyroid drugs like propylthiouracil and carbimazole have no place in this treatment, because the thyroid is not making excessive hormones long-term.

Often, the only treatment needed is aspirin or a non-steroidal anti-inflammatory agent, such as ibuprofen. Once in a while, using a corticosteroid, such as prednisolone, is necessary for a week or two. When the uptake of radioactive iodine returns to normal, the inflammation is finished, and any corticosteroids are stopped.

With the end of symptoms, the patient is back to normal permanently in almost every case. Like so much in medicine, rare exceptions do arise where the disease goes away and then returns or the pain is persistent. In these rare cases, removing the thyroid may prove necessary to finally control the disease.

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Coping with Postpartum

and Silent Thyroiditis

Michelle is a 29-year-old woman who has a healthy 5-month-old baby boy. She notices that her neck is larger than before, but it’s not painful. She is feeling nervous, her hands shake, and she feels her heart beating rapidly at times.

She has trouble going to sleep, which makes her situation tough because the baby often wakes her up at night, too.

Michelle sees her family doctor, who examines her and tells her that she is probably hyperthyroid. The doctor notes that Michelle was pregnant recently and requests thyroid function tests, which are elevated. After referral to the thyroid specialist clinic, Michelle finds out that she probably has postpartum thyroiditis. The consultant places her on the beta-blocker called propranolol, which controls her symptoms well. The consultant also explains that she will probably go through a phase of low thyroid function before returning to normal.

Several weeks after seeing the consultant, Michelle notices that she’s feeling cold and having trouble keeping awake. Her GP reassures her that experiencing these symptoms is the hypothyroid phase of postpartum thyroiditis and, within a few weeks, she feels normal. Two years later, after a second pregnancy, the problem recurs.

Understanding the disease