Clinical Practice Guideline

HYPERTHYROIDISM

Developed for the

Aerospace Medical Association

by their constituent organization

American Society of Aerospace Medicine Specialists

 

Overview: Gravesí disease is the most common cause of hyperthyroidism.Other variants of hyperthyroidism include toxic nodular goiter and toxic adenoma, or Plummerís 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 Gravesí 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 Graveís 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