Synthroid Does Not Trigger Sjögren Syndrome
Synthroid (levothyroxine) does not trigger or cause Sjögren syndrome; rather, these two conditions frequently coexist because they share common autoimmune pathogenic mechanisms and genetic predispositions. The relationship is one of association, not causation—patients with Sjögren syndrome have an increased risk of developing autoimmune thyroid disease requiring levothyroxine treatment, but the medication itself is not a trigger for Sjögren syndrome 1, 2, 3.
Understanding the Relationship Between These Conditions
The Association is Bidirectional but Not Causal
Sjögren syndrome patients have a 3-fold increased risk of developing thyroid disease compared to the general population, with autoimmune thyroid disease being 3.48 times more common in Sjögren syndrome patients 3.
Hypothyroidism is the most common autoimmune disease that develops in Sjögren syndrome patients during long-term follow-up, occurring in approximately 17.9-45% of cases depending on the study population 1, 2.
Primary Sjögren syndrome is ten times more frequent in patients with autoimmune thyroid disease, and conversely, autoimmune thyroiditis is nine times more frequent in primary Sjögren syndrome patients 4.
Why These Conditions Occur Together
The coexistence reflects shared pathogenic mechanisms rather than one causing the other:
Both conditions share common genetic predisposition and immunogenetic factors, with similar autoimmune mechanisms targeting different exocrine tissues 4.
Antigens are shared by both thyroid and salivary glands, which may explain the frequent association between these diseases 4.
Patients with Sjögren syndrome who develop thyroid disorders typically have positive antithyroglobulin, antithyroid peroxidase antibodies, rheumatoid factor, and anti-Ro/SSA antibodies, indicating a broader autoimmune dysregulation 1, 4.
Clinical Implications for Management
Screening Recommendations
All patients with Sjögren syndrome should be screened for thyroid disease using thyroid function tests (TSH, free T4) and antithyroid antibodies (anti-TPO, anti-thyroglobulin), as thyroid dysfunction or autoimmune thyroiditis is a known associated condition 5, 2.
Patients with Sjögren syndrome complicated by abnormal thyroid function may have more severe immune disorders, including anemia, leukopenia, renal involvement, increased ESR, and decreased complement C4 levels 1.
Treatment Considerations
Levothyroxine supplementation is recommended for hypothyroidism in Sjögren syndrome patients just as it would be for any patient with thyroid dysfunction 6, 7.
The presence of hypothyroidism in Sjögren syndrome patients may indicate more severe disease and warrants closer monitoring for other systemic complications 1.
Important Caveats
Do not discontinue levothyroxine in patients with both conditions, as the thyroid hormone replacement is treating the hypothyroidism, not causing the Sjögren syndrome 7.
The timing of diagnosis matters for understanding the relationship: if Sjögren syndrome develops after years of levothyroxine therapy, this reflects the natural progression of autoimmune disease clustering, not a drug-induced phenomenon 4.
Approximately 10% of patients with clinically significant dry eye have underlying Sjögren syndrome, so maintain a low threshold for serological workup in patients presenting with sicca symptoms, regardless of their thyroid status 8.