A number of studies show that respiratory function is often impaired in conditions of hyperthyroidism, hypothyroidism, nodular goiter and thyroid cancer. In addition, certain treatments, particularly radioiodine, can injure the lungs. The lungs are the primary target of the SARS-CoV-2 virus, which causes Covid-2019. Maintaining optimal thyroid hormone levels is especially important now.

Common symptoms in hypothyroidism include fatigue, exercise intolerance, sleep apnea, and shortness of breath. Some patients with hypothyroidism can experience alveolar hypoventilation, and in extreme cases where myxedema coma occurs there may be marked conditions of hypercapnia (excess carbon dioxide caused by inadequate respiration). Hypothyroid patients who stop using thyroid replacement hormone for three weeks experience a significant decrease in pulmonary function, which can be reversed with the resumption of replacement hormone. In addition, a weakness of skeletal muscles often in seen in hypothyroidism contributes to respiratory problems and improves with treatment.

Nearly seventeen percent of patients with idiopathic pulmonary fibrosis are reported to have hypothyroidism. An autoimmune connection is suspected but not yet confirmed. In addition, both hypothyroidism and hyperthyroidism are commonly seen in conditions of pulmonary hypertension.

Respiratory changes seen in hyperthyroidism include increased oxygen consumption; increased carbon dioxide production, tachypnea (fast breathing), respiratory muscle weakness, and high-output congestive left ventricular failure.

Radioiodine ablation (RAI), especially when used in high doses in thyroid cancer, but also in RAI used to treat hyperthyroidism is reported to injure the lungs, causing pulmonary fibrosis. Fibrosis may occur over 30 Gy.

Resources:

Braverman, E and R Utiger.  Werner & Ingbar's The Thyroid Eighth Edition, 2000.

Johnson, Douglas, Ross, Douglas, and Jean Mulder. "Respiratory Function in Thyroid Disease." UpToDate Dec. 2019. https://www.uptodate.com/contents/respiratory-function-in-thyroid-disease

Rubino, et al. "Late Effects of Radioiodine (I-131)". British Journal of Cancer. 2003

Dutt, N, Purohit, S, and S Lokesh. "Idiopathic Pulmonary Fibrosis and Hypothyroidism; Cannot forget subclinical disease and difficult-to-eliminate corticosteroids." Chest Feb. 2016, 139 (2): 600.