Subacute thyroiditis following seasonal influenza vaccination

abstract

A peritoneal dialysis patient who experienced a repeating attack after a vaccination for influenza while she was being followed and treated succesfully for subacute thyroiditis (SAT) is presented. This case shows SAT as a rare condition following vaccination.. Thus, SAT should be considered as a possible outcome following influenza vaccination and flu-like syndrome.

Dear Editor,

Subacute thyroiditis (SAT) is an inflammatory disorder that is diagnosed based on clinical and laboratory findings, including pain in the thyroid region, symptoms of hyperthyroidism, a low thyroid-stimulating hormone (TSH) level, low thyroid uptake of radioactive iodine, and an elevated erythrocyte sedimentation rate (ESR). Tissue diagnosis is rarely required.¹ Numerous conditions—especially infections—can cause SAT; however, only a few cases of SAT following vaccination have been reported.

Case

A 28-year-old female with a 9-year history of dialysis presented to the nephrology polyclinic. She reported having had an upper respiratory tract infection 2 months earlier and a 3-week history of pain in her thyroid lodge. Her thyroid was palpable and tender. She was diagnosed as SAT based on elevated ESR (72 mm h⁻¹), white blood cell (WBC) count (11.100 µL⁻¹, 75% neutrophils), C-reactive protein (CRP) (45 mg dL⁻¹), TSH (40.1 µIU mL⁻¹), and anti-TG-TPO, and supportive ultrasonographic findings. She was started on ibuprofen 1800 mg d⁻¹ (t.i.d.) following consultation with the nephrology department. Her symptoms were completely resolved 1 week after the start of treatment and she was then given levothyroxine 75 μg d⁻¹ and follow-up.

She presented to hospital 3 months later with fatigue, fever, sore throat, dyspnea, and pain and swelling in her thyroid lodge. Ultrasonography showed an enlarged thyroid. In addition, her ESR (126 mm h⁻¹), CRP (98.5 mg dL⁻¹), anti-TG, and anti-TPO were very high. Anamnesis showed that she received an influenza vaccination 3 weeks earlier, developed influenza-like symptoms 3 d post vaccination, and developed pain and swelling of the thyroid 2 weeks post vaccination. Thyroid scintigraphy showed heterogenous tissue and low-level activity; subsequent thyroid biopsy findings were consistent with SAT and the patient was diagnosed as SAT. Levothyroxine was then increased to 100 μg d⁻¹ and ibuprofen was added. Methylprednisolone 40 mg d⁻¹ was added 3 d later due to lack of symptomatic improvement. The patient's symptoms began to resolve 3 d after starting methylprednisolone and were completely resolved after 1 week. Methylprednisolone was gradually tapered, and then withdrawn after the third week of treatment.

Discussion

SAT is associated with numerous etiologies; however, viral infection (Coxsackie, influenza, etc.) is the most common.^2,3 Thyroid inflammation in patients with SAT is thought to be the result of cytolytic T-cell recognition of viral and cell antigens present in an appropriate complex;³ however, the development of SAT during the period following vaccination for viruses (influenza and hepatitis B) is a rarely-reported clinical entity. Influenza-like symptoms are known to develop after vaccination because of viral antigens. Similarly, vaccination theoretically might trigger subsequent alterations in the thyroid, such as viral agents. The literature includes only 4 reported cases of SAT following vaccination (influenza: n= 2; hepatitis B: n= 1; H1N: n = 1).^4-7 To the best of our knowledge the presented case is the fifth patient with SAT following viral vaccination. In the presented patient the first episode of SAT was probably due to influenza virus infection. After completely recovering from the flu (complete resolution of clinical and laboratory findings of SAT) the patient received influenza vaccine, and a short time later a flu-like syndrome developed followed by a second episode of SAT. As there was no evidence of recent infection prior to the second episode of SAT and because the clinical findings occurred soon after influenza vaccination, we strongly suspected that the second episode of SAT was directly related to the influenza vaccine or that the recurrence of SAT was aggravated by influenza vaccination, but more precise methods are required to determine this possibility. SAT rarely recurs after complete recovery. Previously reported vaccine-associated cases of SAT did not have recurrent episodes of SAT, except for 1 case reported by Hsiao et al.⁵ They reported a 25-year-old female that received influenza vaccine and subsequently developed SAT. She had a history of a similar episode of SAT 12 y earlier and the researchers concluded that the recurrent episode might have been induced by influenza vaccine injection due to delayed hypersensitivity reactions via sensitized lymphoid cells, which differs from the etiology hypothesized in the presented case.

The presented case is a rare example of SAT following viral vaccination causing subacute thyroiditis, similarly to what the virus can do. Based on the presented case, we think that SAT should be considered in all patients that receive influenza vaccine and subsequently develope flu-like syndrome and thyroid pain. In addition, if patients have a positive history of SAT close observation for recurrent SAT is warranted.

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.