What respiratory findings are associated with hypothyroidism (underactive thyroid disease)?

From the Guidelines

Patients with hypothyroidism typically exhibit respiratory findings such as hypoventilation, sleep apnea, pleural effusions, and respiratory muscle weakness due to decreased metabolic rate and altered fluid dynamics. These findings are supported by the study 1, which notes that the hemodynamic changes typical of hypothyroidism are opposite to those of hyperthyroidism, but are accompanied by fewer symptoms and signs. The most common signs are bradycardia, mild hypertension, and a narrowed pulse pressure. Some key respiratory findings in hypothyroidism include:

• Hypoventilation with shallow, slow breathing patterns and reduced respiratory drive
• Sleep apnea, particularly obstructive sleep apnea, which occurs in up to 30% of hypothyroid patients
• Pleural effusions, often presenting as bilateral exudative effusions
• Respiratory muscle weakness leading to decreased respiratory muscle strength, reduced lung volumes, and impaired respiratory function tests
• Dyspnea on exertion and increased risk of respiratory infections due to impaired immune function
• Pulmonary hypertension secondary to chronic hypoxemia The study 1 also notes that clinical heart failure is rare in hypothyroidism, because the cardiac output is usually sufficient to meet the lowered systemic demands. However, it is essential to note that the evidence from study 1 is not directly relevant to the question of respiratory findings in hypothyroidism, as it focuses on cancer care for transgender and gender-diverse people. Therefore, the recommendation for patients with hypothyroidism is to monitor for these respiratory findings and manage them appropriately, usually with thyroid hormone replacement therapy, such as levothyroxine, at individualized doses based on TSH levels 1.

From the FDA Drug Label

• Respiratory:dyspnea The patient with hypothyroidism may experience dyspnea, which is a respiratory finding.

• Dyspnea is a symptom of shortness of breath. No other respiratory findings are directly mentioned in the drug label as being associated with hypothyroidism. 2

From the Research

Respiratory Findings in Hypothyroidism

• Hypothyroid patients may exhibit a blunted ventilatory response to carbon dioxide stimulation, indicating altered ventilatory control at the neural level 3.
• Studies have shown that hypothyroidism can lead to reduced forced vital capacity, forced expiratory flow, and diffusing capacity of the lungs for carbon monoxide (DLCO) 4.
• Exercise testing parameters, such as maximum oxygen consumption, minute ventilation, tidal volume, and oxygen pulse, may also be significantly reduced in hypothyroid patients 4.
• The respiratory manifestations of hypothyroidism can be attributed to various mechanisms, including:
  • Ventilatory control system dysfunction
  • Diaphragmatic muscle function impairment
  • Pulmonary gas exchange abnormalities
  • Upper airway obstruction due to goiter
  • Decreased capacity for energy transduction
  • Reduced glycolytic activity 5
• Obstructive sleep apnea syndrome has been found in approximately 30% of newly diagnosed patients with overt hypothyroidism, and treatment has been shown to be reversible 5.

Effects of Hypothyroidism on Respiratory System

• Hypothyroidism can affect the respiratory system and control of breathing, with studies suggesting that thyroid hormone replacement therapy may help normalize respiratory function 3, 6.
• Animal models of hypothyroidism have been used to study the effects of hypothyroidism on the respiratory system and control of breathing, including the role of neurotransmitters that influence breathing 6.
• The relationship between hypothyroidism and respiratory function is complex, and further research is needed to fully understand the underlying mechanisms and to develop effective treatment strategies 5.