Is hypothyroidism (underactive thyroid) a cause of Sjogren syndrome?

Is Hypothyroidism a Cause of Sjögren Syndrome?

No, hypothyroidism does not cause Sjögren syndrome—rather, these are two distinct autoimmune conditions that frequently coexist as polyautoimmunity, with Sjögren syndrome patients having a 3-fold increased risk of developing thyroid disease. 1, 2

Understanding the Relationship

The association between Sjögren syndrome (SS) and autoimmune thyroid disease (AITD), particularly Hashimoto's thyroiditis leading to hypothyroidism, represents polyautoimmunity rather than a causal relationship. 1 This means:

• Both conditions are nosologically different diseases that share common pathophysiological mechanisms as part of the autoimmune spectrum, but neither causes the other. 1
• Patients with SS have a significantly elevated risk (OR 3.29,95% CI 2.08-5.21) of developing thyroid disease compared to controls. 2
• The prevalence of autoimmune thyroid disease in primary SS ranges from 24-45%, with subclinical hypothyroidism being the most common hormonal pattern. 3, 4

Clinical Implications for Screening

All patients with Sjögren syndrome should be screened for thyroid dysfunction because: 5, 4

• Thyroid disease occurs in approximately 24-45% of primary SS patients, far exceeding general population rates. 3
• Autoimmune thyroiditis is 9 times more frequent in primary SS, and conversely, primary SS is 10 times more frequent in patients with autoimmune thyroid disease. 4
• Hypothyroidism was the most common autoimmune disease developed during 10.5-year follow-up of SS patients. 4

Distinguishing Features When Both Coexist

When SS and hypothyroidism/Hashimoto's thyroiditis occur together, the clinical presentation shows subtle variations: 1

• Lymphadenopathy and urticaria are more frequent in SS-HT patients compared to SS alone (p < 0.05). 1
• Anti-Ro/SSA antibodies are more common in primary SS without thyroid disease (p = 0.01). 1
• Smoking history is more prevalent in SS-HT patients (p = 0.03). 1

Shared Pathogenic Mechanisms

The frequent coexistence suggests common predisposing factors rather than causation: 1, 4

• Shared antigens between thyroid and salivary glands may explain the association. 4
• Common genetic predisposition has been suggested by immunogenetic studies. 4
• Both conditions predominantly affect women and are associated with positive antithyroglobulin, antiparietal cell, and antithyroid peroxidase antibodies. 4

Management Approach

Co-management with a rheumatologist is essential for all SS patients due to the high frequency of associated autoimmune conditions. 6, 5

Specific screening recommendations include:

• Measure thyroid function tests (TSH, free T4) and thyroid antibodies (anti-thyroid peroxidase, anti-thyroglobulin) in all newly diagnosed SS patients. 5, 3
• Patients prone to develop thyroid disorders can be identified by the presence of thyroid-related autoantibodies or rheumatoid factor and anti-Ro/SSA activity. 4
• Regular monitoring for thyroid dysfunction should continue throughout follow-up. 4

Critical Pitfall to Avoid

Do not assume hypothyroidism symptoms are solely due to thyroid disease in SS patients. 7 Fatigue, for example, is a prominent systemic manifestation of SS itself and occurs independently of thyroid status. 6 Conversely, do not attribute all sicca symptoms to hypothyroidism without evaluating for SS, as approximately 10% of patients with clinically significant dry eye have underlying Sjögren syndrome. 6