| Thyroid
Disease in Late Life |
Index to this Health
Guide
Detecting
Hypothyroidism in the Elderly
Treating Hypothyroidism in Elderly
Detecting Hyperthyroidism in the Elderly
Treatment of Hyperthyroidism in the Elderly
Summary |
Health
Guides on Thyroid Disease
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The risk of thyroid dysfunction increases with age and is most prevalent
in elderly females. Thyroid dysfunction often escapes clinical detection
because its symptoms often mimic those changes associated with aging
itself. Hypothyroidism can be masked by the clinical features which
it shares with the symptoms of aging that include a general slowing
of mental and physical function, tendency to low body temperatures
and cold intolerance, weight gain, constipation, hardening of the
arteries, elevation of serum lipids (cholesterol), elevation of
blood pressure and anemia. Apathetic (indifferent) behaviour may
be part of aging but may also be the presenting finding of hyperthyroidism
in the elderly. Hyperthyroidism, with its associated irregular heart
rhythms, congestive heart failure, nervousness, sweating, weight
loss and muscle weakness, may also be misinterpreted as part of
the aging process.
Owing to the atypical,
non-specific and meagre clinical findings that may occur for thyroid
disease among the elderly, appropriate recognition depends upon
a high index of suspicion on the part of the clinician and confirmation
by appropriate laboratory testing. However, the interpretation of
thyroid tests requires a familiarity with the minimal reductions
in circulating levels of thyroid hormones associated with aging,
itself. In addition, co-existing decreases in caloric intake, acute
and chronic nonthyroidal illnesses as well as a variety of pharmacologic
agents and x-ray dyes also affect their interpretation. Such conditions
may modify thyroid tests to either mask existing thyroid dysfunction
or induce changes which simulate abnormal results by spuriously
increasing or decreasing circulating levels of thyroid hormone concentrations
[(thyroxine T4) or L-triiodothyronine (T3)] as well as levels of
pituitary thyroid stimulating hormone (TSH). When these complicating
factors are excluded, the usual normal ranges for younger adults
with slight modifications for age should suffice in diagnosing both
hypothyroidism and hyperthyroidism. In particular, newly devised
methods for measuring serum TSH by ultrasensitive methods have improved
the early detection of thyroid dysfunction in the elderly, especially
when the above mentioned complicating factors have been excluded.
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Detecting
Hypothyroidism in the Elderly
When hypothyroidism
is suspected in the elderly, a serum T4 and T3 Uptake (T3U) assay
should be performed in conjunction with a routine measurement of
serum TSH. In typical primary hypothyroidism, the T4 and T3U tests
are below normal and the serum TSH increased. Routine screening
of elderly populations (greater than 60 years of age) not uncommonly
detects increases in serum TSH among approximately 15-20% of such
subjects, with females having a 3-4 fold greater risk compared to
males. However, the majority of elderly subjects detected by TSH
screening are relatively asymptomatic and have a serum TSH level
at less than 10 mIU/L ( with upper limit of normal being 3.5 mIU/L).
It is estimated that among such patients with moderate increases
in TSH, only 50% will have symptomatic improvement following a cautious
trial of thyroid hormone replacement therapy; whereas, those who
are more severely affected, (serum TSH levels usually greater than
20 mIU/L) often have a dramatic improvement in mental and physical
function following appropriate treatment.
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Treating
Hypothyroidism in the Elderly
In the treatment of
hypothyroidism in the elderly, those patients with minimal elevations
of serum TSH but normal serum T4 and T3U levels, may not require
immediate treatment unless there is a large goitre. Therapy may
also be withheld when there are other complicating conditions such
as heart disease. In general, the institution of thyroid hormone
replacement therapy commences with L-thyroxine (L-T4) tablets at
small initial doses of between 12.5 to 25 micrograms/day. The L-T4
dosage is increased at six weeks intervals to a maximum daily dose
of approximately 75-125 micrograms/day to avoid complications of
excessive replacement therapy such as nervousness, sweating, heat
intolerance, weight loss, palpitation and chest pain. Usually, L-T4
is administered at a dosage sufficient to normalize serum T4 to
mid-normal levels and restore serum TSH levels to the upper ranges
of normal. However, in the elderly, the average replacement dosage
is less than in younger adults particularly when there is co-existing
cardiovascular disease. It has been well established that elderly
patients with longstanding hypothyroidism that began in adulthood
often will require a reduction of the daily maintenance dosage in
later life. In particular, postmenopausal females receiving L-T4
dosage that suppresses the TSH level, could be at risk for increasing
the degree of reduced bone density (osteoporosis) that commonly
occurs in the elderly.
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Detecting
Hyperthyroidism in the Elderly
In the absence of possible
coexisting systemic illness and pharmacologic drug interference,
a low or suppressed TSH level indicates hyperthyroidism. Serum total
T4 and T3U are routinely measured to determine the degree of hyperthyroidism.
As well, serum T3 test is often obtained to detect a subtle type
of hyperthyroidism known as the "T3 toxicosis syndrome" which may
occur in elderly subjects who have either single or multiple hyperfunctioning
thyroid nodules. When a diagnosis of hyperthyroidism is confirmed
by clinical and laboratory evaluation, a radioisotope thyroid uptake
and scan test should be subsequently performed to determine which
of the various causes of hyperthyroidism is present, in order to
assist in selecting the appropriate treatment.
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Treatment
of Hyperthyroidism in the Elderly
Most commonly hyperthyroidism in the elderly is
caused by the overproduction of thyroid hormone within the thyroid
gland due to either a diffusely overactive thyroid gland (Graves'
disease) or, alternatively, by a hyperfunctioning solitary or
multiple thyroid nodules or lump (i.e toxic nodular goitre). Such
causes of hyperthyroidism in the elderly are optimally treated
by the initiation of antithyroid medication (propylthioracil or
methimazole) to block the thyroid hormone production. Also, sedatives
and beta blocker medication (to reduce nervousness, tremor, sweating,
and rapid heart rate) may be used with caution in the elderly
to non-specifically control hyperthyroid symptoms until the antithyroid
drugs restore the patient to normal. Once thyroid function has
been normalized for three to six months on such medication, a
more definitive therapy is usually selected to permanently relieve
excessive thyroid gland function. Most commonly, radioactive iodine
is given after discontinuing thionamide drugs for 7-14 days prior
to its administration. When Graves' disease is treated with radioactive
iodine, hypothyroidism often occurs but is less commonly observed
when radioiodine is used for hyperfunctioning thyroid nodules.
Should hypothyroidism occur, appropriate L-T4 replacement therapy
is subsequently instituted. When there is a concern that hyperthyroidism
coexists with a hypofunctioning thyroid nodule, (and the consequent
risk for underlying malignancy) surgery may be selected as definitive
therapy to deal with both problems simultaneously. After appropriate
surgery, long-term L-thyroxine replacement therapy will be indicated
if there is subsequent hypothyroidism.
Hyperthyroidism in the elderly may also be secondary
to a destructive inflammatory process in the thyroid gland associated
with pain (typical subacute thyroiditis - de Quervain's syndrome).
Subacute thyroiditis is believed to be secondary to an infection
(often due to a viral cause). Alternatively, a painless thyroiditis
(underlying Hashimoto's thyroiditis) can also cause hyperthyroidism.
Such hyperthyroidism may be suspected by its association with
a suppressed radioactive iodine thyroid uptake test. The hyperthyroidism
spontaneously resolves over weeks to months. These causes of hyperthyroidism
only require therapy directed at the temporary symptoms and signs
of hyperthyroidism by using sedatives and/or beta blocker drugs
until the hyperthyroidism has resolved spontaneously. However,
when the inflammation is severe, there is risk 2-4 months later
of transient hypothyroidism that may require L-thyroxine replacement
therapy for 6-12 months until thyroid gland function recovers.
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Summary
Since it
may mimic the symptoms and signs of aging, the clinical recognition
of thyroid dysfunction in the elderly requires a high index of suspicion.
Although the standard tests used to monitor thyroid function may
be slightly altered by aging, the "normal ranges" used for younger
adults can be applied for diagnosing thyroid dysfunction in the
elderly when factors of concurrent acute or chronic illness, changes
in nutritional and mental status as well as the possible recent
administration of x-ray dyes and drugs have been excluded.
Treatment of thyroid dysfunction
in the elderly compared to younger patients, does require special
considerations. Generally, L-thyroxine therapy for the treatment
of hypothyroidism is initiated at low dosage and the eventual long
term maintenance dose required to restore elderly subjects to normal
is less than that necessary for younger patients. The treatment
of hyperthyroidism in the elderly requires the routine restoration
of thyroid function to normal for 3-6 months using antithyroid drugs
(propylthioracil or methimazole) prior to administering either radioactive
iodine or surgery to permanently eliminate the possibility of recurrent
hyperthyroidism. |
Written
by Paul G. Walfish, CM, MD, FRCP(C), FACP, FRSM, Professor of Medicine
& Pediatrics, University of Toronto, Mount Sinai Hospital, Toronto.
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