Is chronic urticaria linked to thyroid autoimmune disease?

Chronic Urticaria and Thyroid Autoimmune Disease: The Connection

Yes, chronic urticaria is significantly linked to thyroid autoimmunity, with thyroid autoantibodies being present in approximately 14-36% of chronic urticaria patients compared to 6% in the general population. 1, 2

Evidence for the Association

The relationship between chronic urticaria and thyroid autoimmunity is well-established in current guidelines:

• The 2022 international urticaria guidelines specifically recommend measuring IgG anti-thyroid peroxidase (anti-TPO) levels as part of the basic diagnostic workup for chronic spontaneous urticaria (CSU) 1
• The British Journal of Dermatology guidelines note that thyroid autoimmunity in chronic ordinary urticaria (COU) occurs in 14% of patients versus 6% in population controls 1
• Current practice guidelines recommend screening for thyroid autoantibodies and thyroid function tests in patients with chronic urticaria, especially if an autoimmune etiology is suspected 1, 2

Clinical Significance

The association has several important clinical implications:

• A high ratio of IgG-anti-TPO to total IgE is currently considered the best surrogate marker for autoimmune CSU 1
• Patients with autoimmune CSU are more likely to have low total IgE levels and elevated levels of IgG-anti-TPO 1
• These biomarkers may serve as prognosticators for treatment outcomes with therapies like omalizumab or cyclosporin 1

Diagnostic Approach

For patients with chronic urticaria, guidelines recommend:

1. Include thyroid autoantibodies (anti-TPO) and thyroid function tests in the diagnostic workup, particularly for:

   • Patients with more severe disease not responding to H1 antihistamines 1
   • Cases where autoimmune etiology is suspected 1, 2
   • As part of the "7 Cs" diagnostic approach (Confirm, Causes, Cofactors, Comorbidities, Consequences, Components, Course) 1

2. Consider the IgG-anti-TPO to total IgE ratio as a marker for autoimmune CSU 1

Treatment Considerations

While the exact pathogenic mechanism linking thyroid autoimmunity and chronic urticaria remains unclear:

• Some case reports suggest improvement of urticaria with levothyroxine treatment in patients with marginal thyroid function abnormalities 3
• Screening for thyroid autoimmunity is considered useful in all patients with chronic urticaria for early identification of those requiring treatment of underlying thyroid dysfunction or follow-up 4, 5

Common Pitfalls to Avoid

1. Not screening for thyroid autoimmunity: Given the established association, failing to check thyroid antibodies and function in chronic urticaria patients may miss an important comorbidity.

2. Assuming causality: While there is a clear association, there is insufficient evidence that thyroid antibodies directly cause urticaria. Most likely these are associated, parallel autoimmune events 4.

3. Overlooking euthyroid patients: Thyroid autoantibodies may be present even in euthyroid patients with chronic urticaria 4, so normal thyroid function tests should not preclude antibody testing.

4. Focusing only on idiopathic cases: Some studies suggest thyroid autoimmunity may be associated with both idiopathic and known-cause chronic urticaria 5.

The weight of evidence clearly supports screening for thyroid autoimmunity in patients with chronic urticaria, as this may identify an important associated condition that could influence management approaches.