Introduction

Although thyroid function does not change specifically with age, there are ways in which the diagnosis and treatment of thyroid conditions become more complicated as patients get older. A recent review has summarized these, together with some of the pitfalls facing the family practitioner in interpreting thyroid lab results.

Diagnosis of thyroid disorders is usually confirmed, and treatment monitored, by measuring thyroid function. Diseases in old age (e.g. malnutrition, poorly controlled diabetes, liver disease, heart failure, malignancy) can cause low serum total and free triidothyronine (T3), total and free thyroxine (T4), and raised or suppressed thyrotrophin (TSH).

Drugs commonly taken by elderly patients can:

• produce lowered free T4 with lower or normal T3 and normal TSH (phenytoin, carbamazepine, phenobarbitone),
• increase free T4 and T3 with lower TSH (aspirin, phenylbutazone, heparin)
• cause lowered or normal free T4 and T3 with lowered TSH (corticosteroids, dopamine)

Drugs can, of course, cause hyperthyroidism (amiodarone, iodine ingestion [kelp], contrast media, alpha-interferon, interleukin 2) or hypothyroidism (lithium, amiodarone, iodine ingestion, aminoglutethamide, alpha-interferon, interleukin 2) by a direct effect on the gland itself.

Finally, the clinical picture of thyroid disease in the elderly is easy to confuse with some of the normal process of aging and other diseases of older persons.

Hypothyroidism in the elderly

The usual cause is autoimmune disease resulting in goitrous or atrophic thyroiditis. The classis symptoms are often absent, and others may be confused with signs of normal aging. On the other hand, neurological (cerebellar dysfunction, neuropathy) and psychiatric symptoms (depression, behavioral and cognitive impairment) are more common in the elderly, as is the risk of myxedematous coma.

The diagnosis should be considered if there is unexplained hyponatremia, increased creatinine phosphokinase, lactic acid dehydrogenase and macrocytic anemia. A fall in total or free T4 with a rise in TSH is diagnostic for primary hypothyroidism. Reduced hormone levels with a normal TSH suggest a non-thyroid disease or drug-induced cause (see above).

Treatment with thyroxine at a daily dose of 50-100 micrograms for 6-8 weeks should bring the patient to a euthyroid state (i.e. the serum T4 and TSH levels are normalized). Monitoring of the TSH level is required, as thyroxine replacement can precipitate angina or myocardial infarction, while suppressing the TSH below normal levels has been associated with an increased risk of osteoporosis and atrial fibrillation.

Thyroxine should be continued for life, with annual TSH levels done to check for adequate dose or compliance. Referral for specialist review is usually only necessary if there is myocardial ischemia, the need for amiodarone or lithium therapy, or evidence of pituitary disease.

Hyperthyroidism in the elderly

Most cases are due to toxic nodular goiter, Graves' disease, or a solitary toxic nodule; less commonly subacute or silent thyroiditis and iodine-induced thyrotoxicosis may be responsible. Some geographical areas may still provide areas of iodine deficiency - parts of Germany and East Europe.

Some elderly hyperthyroid patients may show very few signs or symptoms - this is called "apathetic hyperthyroidism". The classical eye signs (ophthalmopathy) are often absent in the elderly. On the other hand, congestive cardiac failure is a common finding (60%) in older patients with hyperthyroidism, along with refractory atrial fibrillation. Weight loss with anorexia, rather than increased appetite, is seen, and there may be signs of depression, lethargy, dementia and confusion.

Examination reveals a goiter in 25-50% of cases, with lab tests showing raised serum total and free T4 with a lowered TSH value. (Rarely, the TSH is low and the T4 normal - serum T3 should be determined in such patients to exclude possible "T3-toxicosis".) The possible effect of concomitant diseases of the elderly and drugs on the thyroid test results must be remembered (see above).

The authors of this review recommend that all elderly patients with hyperthyroidism be referred to a specialist. Initial treatment, until a more definitive plan is determined, may include a thionamide (methimazole, carbimazole or propylthiouracil) and a beta-blocking drug. Thionamide treatment has a 50% recurrence rate in Graves' disease and is ineffective in toxic nodular goiter, so definitive treatment is needed in most elderly patients.

After a euthyroid state is reached (usually 1-6 months of a thionamide, with monthly serum T4 checks), administration of radioiodine or surgery can be undertaken. Radioiodine therapy is relatively risk-free, although there may be transitory hyperthyroidism associated with pain, tenderness and swelling of the gland; it may have to be repeated, in some patients. Surgery is usually reserved for older patients with a large goiter or ophthalmopathy.

Nodular goiter and thyroid cancer in the elderly

Thyroid nodularity increases with age, so that most persons over 80 have a nodular thyroid - this is more likely in women than in men. The incidence of differentiated thyroid cancer does not increase with age, but a rare anaplastic carcinoma involving the gland is recognized exclusively in patients over 65. Surgery, external radiation and chemotherapy are all used in treatment, depending on the individual pathology and spread.