Thyroid gland disorders that are of aeromedical concern consist of hypothyroidism, hyperthyroidism (thyrotoxicosis), thyroid cancer and occasionally large goitres with obstructive symptoms. Cancer will be discussed in the oncology chapter.
Hypothyroidism may be result of impaired production of TSH in the context of pituitary disease. Thyroiditis, surgical ablation and radio-iodine ablation are far more common causes. In these latter situations the TSH is always elevated before the T4 is reduced. In pituitary disease the TSH will not be significantly elevated and T4 determination is necessary.
Symptoms may include fatigue, weight gain, dry skin and bradycardia. Constipation is not uncommon as is periorbital puffiness. Myxoedema, heart failure and rarely coma may occur.
Treatment is via lifelong thyroid replacement, titrated until clinical and biological stability are achieved, as demonstrated by normalisation of the TSH (and T4 in the case of pituitary disease). The usual daily dose of Thyroxine is around 100 to 150 mcg. The rare omission of medication should not result in any acute impairment. This makes this treatment acceptable in the aviation context. Lifelong, twice yearly, TSH biochemical surveillance is required, to include T4 in the case of pituitary disease, once stability is achieved.
Hyperthyroidism is often due to autoimmune Grave’s disease or a toxic nodular goitre, or occasionally medication, including iodine.
In Grave’s disease the antibodies attach to the TSH receptors causing the release of thyroid hormone from the gland. Toxic nodular goitre and toxic adenoma also result in excessive thyroid endocrine activity. TSH will be decreased and T4 / freeT4 and T3 / freeT3 are increased.
Symptoms may include Insomnia, tremor, weight loss, nervousness, lethargy and palpitations including atrial fibrillation. Eye changes including redness, lid retraction and proptosis may result in heterophoria or diplopia in severe cases. Beta-blockers (Propranolol or Metoprolol) are effective in giving rapid relief of palpitations and tremor. Carbimazole or Propyl Thiouracil control thyroid hormone overproduction but can take 2-3 weeks to respond. Therapy for 12 months or so is often required. There is at least a 50% relapse once medication is stopped.
More definitive therapy includes total thyroidectomy or radioiodine ablation, both resulting in hypothyroidism which is permanent after surgery and often permanent after radio iodine. This generally requires lifelong surveillance and treatment.
Goitre: The presence of goitre not causing functional impairment, such as obstruction of airways or swallowing is of little aeromedical significance provided that thyroid endocrine function is not impaired and malignancy has been excluded.
On the first occasion that an applicant presents with a history of thyroid disease;
On subsequent occasions that an applicant presents with a history of thryoid disease:
An applicant who presents with hypothyroidism treated may be considered as having a condition that is not of aeromedical significance if: