Can hypothyroidism cause pleural effusion, and if so, what type and how?

Hypothyroidism and Pleural Effusion

Yes, hypothyroidism can cause pleural effusion, typically presenting as an exudative or borderline exudate-transudate effusion that results from increased capillary permeability, altered albumin distribution, and reduced lymphatic drainage. While not as common as pericardial effusion in hypothyroidism, pleural effusion can occur in severe or long-standing cases of hypothyroidism.

Mechanism of Pleural Effusion in Hypothyroidism

The pathophysiological mechanisms by which hypothyroidism leads to pleural effusion include:

1. Increased capillary permeability - Thyroid hormone deficiency alters vascular permeability, allowing proteins to leak into the pleural space 1, 2

2. Altered albumin distribution - Changes in albumin distribution volume contribute to fluid accumulation 3

3. Reduced lymphatic drainage - Impaired lymphatic clearance in the pleural cavity 3, 4

4. Inappropriate antidiuretic hormone secretion - Can contribute to fluid retention 2

5. Associated heart failure - Hypothyroidism can cause heart failure which independently leads to pleural effusion 1

Characteristics of Hypothyroidism-Related Pleural Effusions

• Type: Most commonly exudative or borderline between exudate and transudate 5
• Appearance: Usually serous in nature 5
• Inflammatory markers: Show little evidence of inflammation 5
• Distribution: Can be unilateral or bilateral, and may occur alongside pericardial effusion and ascites 2

Diagnosis

When evaluating pleural effusions in a patient with suspected hypothyroidism:

1. Thoracentesis: Analyze pleural fluid using Light's criteria to differentiate between transudate and exudate 6

2. Laboratory tests: Check thyroid function tests, particularly TSH levels 4

3. Exclude other causes: Rule out other common causes of pleural effusion such as heart failure, malignancy, and infection 6, 7

4. Additional imaging: Consider echocardiography to evaluate for concurrent pericardial effusion, which is more common in hypothyroidism (3-37% incidence) 4

Management

The primary treatment for hypothyroidism-induced pleural effusion is:

1. Thyroid hormone replacement therapy: This is the definitive treatment and often leads to resolution of the effusion 1, 2

2. Drainage procedures: May be required for severe effusions causing respiratory compromise 1

3. Monitor response: Follow up with imaging to ensure resolution of the effusion after initiating thyroid replacement therapy 3

Clinical Pearls and Pitfalls

• Pitfall: Hypothyroidism is often overlooked as a cause of unexplained pleural effusion, especially when other typical symptoms of hypothyroidism are subtle 2

• Pearl: Consider hypothyroidism in the differential diagnosis of unexplained exudative pleural effusions, particularly when accompanied by pericardial effusion and/or ascites 2

• Caution: While most hypothyroidism-related effusions resolve with hormone replacement, severe cases may require drainage, especially when diuretic treatments are insufficient 1

• Important note: The majority of pleural effusions in patients with hypothyroidism are actually due to other diseases, but effusions solely due to hypothyroidism do occur 5