Developed for the
Aerospace Medical Association
by their constituent organization
Overview: Hashimoto’s thyroiditis and thyroid ablative therapy are the most common causes of hypothyroidism. Other causes include neck irradiation, medications and hypothalamic or pituitary deficiency. Onset of symptoms is often insidious; subclinical hypothyroidism is much more common than full-blown myxedema. Symptoms include fatigue, lethargy, physical and mental slowness, apathy, headache, cold-intolerance, arthralgias, myalgias, thick dry skin, hoarse voice, and constipation. Diagnosis is often delayed because of the apathy, which causes patients to minimize complaints. Like hyperthyroidism, a single symptom may dominate the clinical picture. In rapid onset hypothyroidism, myalgias, arthralgias, and paresthesias are often the major symptoms. Other than drug-induced, hypothyroidism is generally progressive and irreversible.
Diagnosis: Laboratory diagnosis is made by determining the TSH and T4 levels. An elevated TSH and low T4 confirm the diagnosis. Serum T3 and RT3U are not helpful in diagnosing hypothyroidism; both are normal in up to 50% of hypothyroid patients.
Therapy: Thyroxine (Synthroid) is used to produce euthyroidism. A normal serum TSH level verifies full thyroid replacement. Patients must be followed on a regular basis indefinitely. A lapse in therapy could result in recurrence of apathy and loss to follow up.
Aeromedical Concerns: The major aeromedical concern is the insidious nature of the disease, which could delay diagnosis until apathy, fatigue, and mental slowness lead to significant performance decrement. This same concern applies during follow-up of treated hypothyroid patients.
Treatment and Aeromedical Disposition: Initial waiver requires endocrine consultation and confirmation of euthyroid status. Annual renewal requires confirmation of euthyroid status. These would be the same requirements for civil airmen. Unless there was some unusual presentation, civil airmen would be required to demonstrate a euthyroid state yearly for First and Second class airmen and with each examination for Third class.
Experience: Almost all flyers with hypothyroidism 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. In the U.S.A.F. as of March 1997, 169 rated officers had received waivers for treated hypothyroidism.
In the FAA as of 2008 there are currently issued 1,521 first-, 1,579 second-, and 4,321 third-class airmen with hypothyroidism.
Rayman, Russell B., Clinical Aviation Medicine, 2nd Edition, Lea & Febiger, Philadelphia, 1990, p. 49.
Scientific American Medicine. CD ROM (SAM-CD) 1997;3(1):21-7.
July 22, 2008