Clinical
Evaluation
Early detection
of a change in health status is the most effective way to lessen
the burden of more advanced disease and enhance survival.
Dr. Barry L. Johnson,
assistant surgeon general and ATSDR assistant administrator, congressional
testimony on the National Cancer Institute's Management of Radiation
Studies (Congressional testimony 1998).
Because I-131 concentrates
in the thyroid gland, evaluation of a patient exposed to I-131 centers
on diseases of the thyroid. Exposure to I-131 can cause thyroiditis,
hypothyroidism, and thyroid neoplasms. The patient might have a
variety of symptoms related to exposure or might have health-related
concerns about past exposure. The occurrence of thyroid diseases
caused by exposure is indistinguishable from those that occur spontaneously.
The patient might not have specific knowledge of the nature of the
exposure, which might have occurred years earlier.
A history and appropriate
physical examination supplemented with laboratory investigation,
imaging studies, and fine-needle aspiration biopsy (FNAB) of the
nodules in question should provide the clinician with sufficient
information to assess the likelihood of malignancy and to advise
his or her patients of appropriate treatment options.
Ultrasound can find
many nodules not palpable during the physical examination. Ultrasound
is being used for thyroid monitoring programs in other countries
where some of the population has been exposed to I-131 releases.
However, the use of thyroid ultrasound in mass screenings for thyroid
nodules is controversial because of its high sensitivity and low
specificity.
If a nodule is identified,
fine-needle aspiration biopsy (FNAB) performed by an experienced
physician with appropriate training and experience is the procedure
of choice. If the cytology of the nodule is malignant or nondiagnostic,
the patient should be referred to a specialist for surgical resection.
Patient
History
- History and physical
exam should focus specifically on signs and symptoms related to
the thyroid gland.
The medical history
should include prior endocrine, thyroid, or parathyroid problems;
prior thyroid diagnostic tests and treatments; and history of thyroid
or neck surgery. Information about changes in the size of the nodule
or nodules can assist in determining the etiology. Nodules that
are unchanged for years are probably benign, but nodules that grow
rapidly demand careful evaluation and are more likely to be associated
with parathyroid disorders.
A family history of
Hashimoto thyroiditis, benign thyroid nodule, or goiter favors a
diagnosis of benign disease. Other history that suggests benign
disease includes symptoms of hypothyroidism or hyperthyroidism,
and pain or tenderness of the nodule. Risk factors for malignant
disease can include a family history of thyroid carcinoma or multiple
endocrine neoplasia type II; the patient's age (<20 years or
>70 years); the patient's gender (male); recent changes in voice,
breathing, or ability to swallow; and a childhood history of head,
neck, or upper mediastinum radiation exposure.
Exposure
History
An exposure history
includes previous childhood head, neck, and upper mediastinum radiation
exposure; previous residences (downwind from or proximity to nuclear
testing or release sites); dietary habits since childhood; source
of drinking water; occupational history; and hobbies. Milk consumption
and source are important risk factors (for example, fresh versus
processed milk; milk from a cow, sheep, or goat). The patient should
be asked about symptoms consistent with hypothyroidism, hyperthyroidism,
and disorders of calcium metabolism.
Exposure to I-131 could
be indicated by the patient's answers to questions in the exposure
history relating to the following:
- previous childhood
head, neck, and upper mediastinum radiation exposure
- previous residences
- dietary habits since
childhood
- milk consumption
and source.
Populations exposed
to I-131 can have a higher prevalence rate for thyroid nodules than
populations that have not been exposed. Patients, especially infants
and children who have been exposed to significant doses of I-131,
are more susceptible to the associated negative health effects.
The major clinical concerns after significant I-131 exposure include
hypothyroidism and thyroid cancer.
Physical
Examination
Physical examination
of the neck and thyroid should evaluate the gland's size, presence
of nodules, and the cervical lymph nodes. The thyroid gland should
be inspected for shape, consistency, and areas of tenderness. Local
examination of the neck is best accomplished with the patient seated
in good light with the neck moderately extended. To facilitate the
examination, the patient should be given a glass of water to assist
swallowing. Auscultation of the neck provides some indication of
the vascularity of the gland. A systolic or continuous bruit is
usually associated with hyperthyroidism. The parathyroid glands
are also susceptible to the effects of I-131 exposure. The presence
of cervical lymphadenopathy, especially in children, might be the
first sign of thyroid cancer. In general, a nodule 1 centimeter
(cm) or greater should be palpable on physical examination.
Signs and symptoms that
should prompt concern include rapid enlargement of a previous or
new thyroid nodule, unilateral vocal cord paralysis, dysphagia,
and dyspnea. A solitary nodule in an otherwise normal gland should
raise the suspicion of thyroid carcinoma. A lesion is probably malignant
if it is adherent to the surrounding structures (trachea or strap
muscles). Palpable cervical lymphadenopathy adjacent to a thyroid
nodule is suspicious for a carcinoma, or it might be the only indication
of metastatic thyroid cancer when no thyroid nodule is palpable.
It would be appropriate
to consult an internist, endocrinologist, a surgeon specializing
in thyroid surgery, or an interventional radiologist when assessing
a patient with a suspicious thyroid nodule and an abnormal screening
evaluation. These specialists can either assist with the interpretation
of the screening results or formulate a management plan for the
patient. (Information about specialists is available from the American
Board of Medical Specialties, which has a Web site at URL: http://www.abms.org/).
Case Study (continued)
The woman is a well-developed,
mildly overweight, well-nourished female who looks her stated age
of 55 years. Palpation of her neck reveals an ill-defined thyroid
that is slightly tender diffusely with a homogenous, rubbery texture.
A 1-cm nodule is just palpable in the left lobe. Auscultation of
the neck reveals no bruits, either over the carotids or over the
thyroid. No cervical nodes are palpable. Chvostek and Trousseau
signs are negative. Hair and skin appear unremarkable, with perhaps
the exception of some puffiness of the face. No evidence of mental
dullness is seen. Deep tendon reflexes are normal without prolongation
of relaxation phase. The rest of the examination is unremarkable.
When requestioned about
specific symptoms of hypothyroidism, your patient admits that she
has felt a bit more tired lately. She has been constipated occasionally
and intolerant of cold. She has gained weight despite eating less.
She attributed these symptoms to aging and had not thought much
about them.
Challenge
questions
7. Which diagnostic
tests are recommended for routine initial screening of thyroid
function?
8. What additional
tests could be obtained for the evaluation of a thyroid nodule?
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