HYPERTHYROIDISM
Developed for the
Aerospace Medical Association
by their constituent organization
American Society of Aerospace Medicine Specialists
Overview: Graves’ disease is the most common
cause of hyperthyroidism. Other variants
of hyperthyroidism include toxic nodular goiter and toxic adenoma, or Plummer’s
nodule.
Typical
presenting symptoms include sweating, heat intolerance, tremor, nervousness,
irritability, difficulty concentrating, insomnia, frequent stools, weight loss
in spite of good appetite, and palpitations.
Patients with Graves’ disease can have severe exophthalmos, which can be
accompanied by follicular conjunctivitis, chemosis, ophthalmoplegia, and vision
loss. Cardiac symptoms include new onset
supraventricular arrhythmias (most often atrial fibrillation) and congestive
heart failure (CHF). Although CHF
associated with hyperthyroidism occurs most often in patients with underlying
cardiac disease, severe hyperthyroidism of itself can cause CHF. Although hyperthyroidism usually produces
multiple symptoms, in some patients one symptom can dominate. Examples of monosymptomatic hyperthyroidism
are myopathy (symmetric weakness and wasting of large muscles, particularly in
older men), extreme weight loss, gonadal dysfunction (oligomenorrhea in women,
impotence or gynecomastia in men), and major personality disturbances.
Diagnosis:
Physical exam may show mild proptosis, lid lag, a goiter, tachycardia, tremor,
and palmar erythema. More than 90% of
hyperthyroid patients have an elevated T4.
However, the specificity of the total T4 assay is much lower than its
sensitivity. Because of this, the free
thyroxine index (FTI) combined with a sensitive TSH assay is the preferred
approach to diagnosing hyperthyroidism. A high FTI with a low TSH confirms the
diagnosis.
Therapy:
Three forms of therapy are available for the treatment of hyperthyroidism:
antithyroid drugs, subtotal thyroidectomy, and radioactive iodine. Almost all patients will become euthyroid on
propylthiouracil or methimazole in one to six months. Side effects include vertigo and drowsiness,
minor to major allergic skin reactions and the rare but potentially fatal
agranulocytosis. Drug treatment is
continued for six to 18 months then discontinued. There is a high rate of recurrence after
cessation of drug therapy. Ablative
therapy is indicated for recurrences.
Surgical treatment is difficult and is declining in popularity. It is useful in females in their reproductive
years and is the treatment of choice for a toxic thyroid adenoma. Side effects include hemorrhage,
hypoparathyroidism, and damage to the recurrent laryngeal nerve. Radioactive iodine (131I) can render almost
all hyperthyroid patients euthyroid if enough is given. Higher doses produce higher initial cure
rates and higher rates of eventual hypothyroidism. Ablative therapy (surgical or I31I) results
in a post-treatment incidence of hypothyroidism of about 2-3% per year. A significant percentage of Grave’s disease
patients treated with drugs alone also become hypothyroid over several
years. All hyperthyroid patients must be
followed indefinitely after treatment for the occurrence of hypothyroidism.
Aeromedical Concerns: The primary concerns of untreated
hyperthyroidism in aviators are cardiac or psychiatric symptoms that could lead
to performance decrement and a flight safety
hazard. Optic neuropathy can occur with
thyroid ophthalmopathy. After treatment,
the main concern is the insidious onset of hypothyroidism. Hypothyroidism can produce apathy and mental
sluggishness, which could degrade performance.
The above
are the same concerns for those in the civil aviation medicine field.
Treatment and Aeromedical Disposition: Endocrinology consultation and
confirmation of euthyroid status is required for initial waiver. Ophthalmology consultation may be required
for exophthalmos or other ocular symptoms.
Annual confirmation of euthyroid status is required for annual waiver
renewal. The
information that the military services require for initial and subsequent
medical certification would be the same for civil aviation. Propylthiouracil and methimazole are both
allowed in civil aviation providing the airman has no side effects and is
euthyroid. Radioactive iodine is also acceptable for treatment in the civil
sector.
Experience: Almost all flyers with
hyperthyroidism adequately treated have been successful in obtaining a waiver
to return to flying. Those who were not
were disqualified for incomplete or unsuccessful treatment or for other
unrelated diagnoses. As of 3/97 ninety
rated military officers had received waivers for treated hyperthyroidism.
The
experience in the FAA as of 2008 is that there are 495 first-, 382 second-, and
802 third-class airmen that were currently issued medical certificates with
that diagnosis.
References:
Rayman,
Russell B., Clinical Aviation Medicine, 2nd Edition, Lea
& Febiger, Philadelphia, 1990, pp. 48-49.
Scientific
American Medicine. CD ROM (SAM-CD) 1997;3(1):9-21.
July 22,
2008