Can Lyme Disease Affect Your Thyroid?

Lyme disease and thyroid problems may occasionally occur together. In rare cases, infection with Borrelia burgdorferi has been associated with autoimmune thyroiditis. In the article “Coexisting Thyroiditis and Carditis in a Patient with Lyme Disease: Looking for a Unifying Diagnosis,” Zarghamravanbakhsh and colleagues describe a patient who developed both Lyme carditis and autoimmune thyroiditis.¹

The case involved a 53-year-old woman who developed symptoms shortly after returning from a trip to Delaware. Although she did not recall a tick bite, she reported multiple encounters with deer during her visit.

Within days she developed headaches, heat intolerance, near-syncope (a feeling that you may faint), and a 5 × 5 cm rash on her chest. One week later her symptoms progressed, including shortness of breath on exertion and palpitations.

She was eventually diagnosed with Lyme carditis after her ECG showed a first-degree AV block.

Lyme Disease and Thyroid Test Abnormalities

The patient also had abnormal thyroid laboratory results. Her thyroid tests showed a high free thyroxine (T4) level and a low thyroid-stimulating hormone (TSH). Notably, her TSH level had been normal four months earlier.

Thyroid peroxidase antibodies were present, while thyroid-stimulating immunoglobulin was not.

“Her iodine-123 thyroid scan and 24-hour uptake showed a decrease in iodine uptake of 1.2%, consistent with thyroiditis,” wrote the authors.

The patient was treated with intravenous ceftriaxone (2 g/day) for presumed Lyme carditis and later completed a 3-week course of doxycycline.

“Autoimmune thyroiditis can be caused by Lyme disease.”

Testing for Lyme disease using Western blot was positive.

Following antibiotic treatment, the patient’s abnormal thyroid function tests normalized, suggesting that the infection may have contributed to the thyroid inflammation.

Evidence Linking Lyme Disease and Thyroiditis

The authors discussed several earlier reports describing thyroid abnormalities in patients with Lyme disease.

• Paparone described a case in which Lyme disease occurred in a patient with primary hypothyroidism.
• Dhliwayo and colleagues reported a 22-year-old woman with Lyme disease whose thyroid tests showed transient thyrotoxicosis and decreased radioiodine uptake.
• Deol and colleagues also described an association between Lyme disease and thyroiditis.

“In our patient, known exposure to the vector, a classic rash on the chest, improvement in the symptoms, and normalization of thyroid function tests after antibiotic therapy support Lyme infection as a cause of carditis and painless autoimmune thyroiditis.”

Important Clinical Considerations

Although Lyme disease may occasionally affect the thyroid, the authors cautioned that thyroid disease itself can produce false-positive Lyme serology and conduction abnormalities in the heart.

Clinicians should therefore carefully evaluate patients with abnormal thyroid tests and suspected Lyme disease to determine whether infection, autoimmune thyroid disease, or another condition explains the findings.