Technetium-99m Thyroid Scintigraphy and Human Leukocyte Antigen - B35 in Sub-Acute Thyroiditis.

INTRODUCTION: Sub-acute thyroiditis possibly caused by a viral infection of thyroid gland is associated with a surge in thyroxine levels of the patient. Women in the younger age group are affected more than men. Markedly decreased radioactive iodine thyroid uptakes in a setting of thyrotoxicosis associated with elevated thyroxine levels and reduced thyroid stimulating hormone levels usually clinches the diagnosis. Patients mostly require symptomatic treatment with non-steroidal anti-inflammatory drugs. Sub-acute thyroiditis is a self-limiting disorder with most of the patients making a complete recovery in a span of three to six months. Being geographically and ethnically different the present studies was undertaken with an objective of understanding the clinical, laboratory and thyroid uptake profiles in patients of SAT during its natural history and also find the extent of genetic influences through its association with HLA B35.
MATERIALS AND METHODS: 32 patients in the age group of 20-59 years diagnosed to have sub-acute thyroiditis were studied. 18 patients out of 32 were subjected to HLA B35 testing. Other laboratory parameters that included hormonal profile and radioactive thyroid uptakes were performed.
RESULTS: Most of the patients were females and in their fourth decade of life. Thyroid stimulating hormone levels were decreased in 32 (100%). A majority of patients had normal anti TPO levels. All the patients had grossly decreased Tc-99m thyroid uptake levels at presentation. HLA B35 test done in 18 patients was reported positive in 10 (55.56%) patients.
CONCLUSION: The present study is unique in having used serial Tc-99m thyroid scintigraphy in patients of SAT. A positive HLA B 35 is associated in a majority of patients conferring genetic susceptibility.

Introduction

Thyroiditis, an inflammation of the thyroid gland, is commonly classified based on its onset and duration as acute, subacute, and chronic.[1] Acute thyroiditis may be due to bacterial (Staphylococcus, Streptococcus, and Enterobacter) of fungal (Aspergilla, Candida, Histoplasma, and Pneumocystis) infection. Iatrogenic acute thyroiditis as sequel to radioactive iodine-131 (I-131) and antiarrhythmic amiodarone are also reported.[1] Subacute thyroiditis (SAT) also termed as granulomatous, giant cell, or de Quervain's thyroiditis is a self-limiting inflammatory disorder of thyroid thought to be caused by viral infection of the thyroid gland often following an upper respiratory tract illness.[12] The common etiological agents implicated are the mumps virus, coxsackievirus, influenza virus, echovirus, and adenovirus.[3] The peak incidence occurs at an age of 30–50 years and women are affected three times more frequently than men.[1] Its incidence is reportedly highest in the summer season.[2] In the active phase, patients of SAT usually present with sore throat, fever, easy fatigability, increased sweating, neck pain, palpitations, tremors, and heat intolerance. A few patients may have a neck swelling.[2345] Several autoimmune phenomena have been described in SAT. Some genetic factors which may make individuals susceptible to certain viral pathogens in the pathogenesis of SAT have also been described.[67] A strong association has been observed between SAT and Human Leukocyte Antigen –B35 (HLA-B35) suggesting a possible genetic role in SAT.[67] Due to apoptosis and loss of follicular integrity, thyroglobulin (Tg), tetraiodothyronine (T4), and iodinated Tg fragments are released into the blood circulation in quantities sufficient to produce clinical thyrotoxicosis accompanied by grossly decreased radioactive iodine uptake (RAIU) of the thyroid gland. During the active phase of SAT, differentiating it from hyperthyroidism may be difficult clinically resulting in a delay in decision regarding an appropriate management strategy. RAIU of the thyroid gland at 2 and 24 h which are grossly decreased or technetium-99m (Tc-99m) thyroid scintigraphy revealing a poorly visualized thyroid gland in a clinical setting of thyrotoxicosis often clinches the diagnosis of SAT. Color flow Doppler ultrasonography may also help to make a distinction between Graves' disease and SAT. In Graves' disease, the thyroid gland is hypervascular, whereas in patients of SAT, the gland has low-to-normal vascularity and is predominantly hypoechogenic.[8] Typically, the thyroid function tests, RAIU of the thyroid gland, and Tc-99m thyroid scintigraphy evolve through three distinct phases over an average period of 6 months from a toxic phase to hypothyroid phase and a final euthyroid phase coinciding with restoration of structural and functional integrity of the follicular epithelium within the affected thyroid gland. Complete resolution is the usual outcome in about 90% of the patients. Permanent hypothyroidism may occur in some patients particularly among those with co-incidental thyroid autoimmunity.[19] During the active phase, patients are usually treated with nonsteroidal anti-inflammatory drugs (NSAID) to control symptoms. Glucocorticoids are sometimes prescribed in patients' refractory to NSAIDs.[13] One or more relapses may occur in a small percentage of patients. Chronic form of thyroiditis is often associated with autoimmunity in Hashimoto's thyroiditis and atrophic thyroiditis. The other rarer forms of chronic thyroiditis encountered are Riedel's thyroiditis and those associated with parasitic infestations with Echinococcus, strongyloidiasis, and cysticercosis.

Materials and Methods

This was a prospective follow-up study done over a period of 1½ years from September 2014 to May 2016. The study group included a cohort of 32 treatment naive patients (23 females and 9 males) diagnosed to have SAT. The inclusion criteria were patients with thyrotoxic features having elevated free T4 and/or decreased thyroid-stimulating hormone (TSH) levels with decreased Tc-99m 15-min thyroid uptake. Patients with a history suggestive of thyrotoxicosis, thyroid/neck surgery, consumption of drugs interfering with thyroid function, radiation therapy to the neck, and radiological investigation with iodinated contrast in the past were excluded from the study. The study was approved by the Hospital Ethics Committee.

Patient preparation and technetium-99m thyroid scanning

All the patients were asked a detailed history before subjecting them to clinical examination. Pregnancy and breastfeeding were ruled out in all female patients. An informed consent was taken before the study. Patients were scanned serially at initial presentation, 3 months, 6 months, and some at even 1 year. Patients were administered 185 MBq of Tc-99m pertechnetate intravenously and scanned after 15 min. The patients were imaged in a supine position under a large field of view gamma camera fitted with a low-energy all-purpose parallel-hole collimator. The pulse height analyzer was centered at 140 KeV ± 20% symmetrical window. A total of three views (anterior, LAO 45, and RAO 45) were acquired on a 128 × 128 matrix size. Each image was acquired for 100 K counts. Patients whose Tc-99m thyroid uptake fell between 0.4% and 7.1% were considered to have normalized and were not scanned further.

Human leukocyte antigen-B35 testing

A total of 18 patients selected randomly were evaluated for HLA-B35. Five milliliters of peripheral venous blood was collected and DNA extracted using DNA extraction kits. HLA-B35 typing was done by polymerase chain reaction (PCR) using histotype sequence-specific polymers. The separation of amplification products was done by agarose gel electrophoresis using 0.5 × TBE buffer and 2.5% gel concentration. Electrophoresis separation was done at 10–12 V/cm for 20–40 min. PCR amplification was visualized using a ultraviolet transillumination (220–310 nm). The visualized amplification was photographed at proper exposure time and aperture so that the bands were drawn sharp and stood against dark background. Only those patient samples were considered positive for HLA-B35 which conformed to the specific band pattern.

Statistical methods

The Statistical Package for Social Sciences SPSS 16, Release 16.0.0 from SPSS Inc. (1989–2007) Chicago, IL, USA, was used for data analysis. All the continuous variables of the study have been described by descriptive statistics such as mean, median, and standard deviation. Categorical variables have been described by frequency and percentages. Student's t-test was used for comparison of continuous variables. All the results have been discussed on 5% level of significance with P < 0.05 considered as significant.

Results

At presentation

The majority (59.3%) of patients were young in the age range of 20–39 years with a mean age of 39.96 ± 12.1 years. There was a female preponderance among the patients with 23 (71.9%), and 9 (28.1%) were male. The most common presenting symptoms [Table 1] included neck pain (93.8%), easy fatigability (90.6%), palpitations (81.3%), increased sweating (78.1%), heat intolerance (65.6%), fever (59.4%), and sore throat (56.3%). No seasonal preponderance was observed in the presentation time of the patients. The laboratory results at presentation in the study participants [Table 2] revealed a subnormal TSH in all the patients with a mean TSH of 0.04 ± 0.05 μIU/ml (normal 0.5–6.5 μIU/ml). The FT4 levels [Table 3] were elevated in 29 (90.6%) patients with a mean FT4 of 2.20 ± 0.90 ng/dl (normal 0.61–1.12 ng/dl). In rest of the 3 (9.4%), FT4 levels were low normal with a mean level of 0.79 ± 0.13 ng/dl. The other correlative laboratory parameters [Table 4] revealed an elevated erythrocyte sedimentation rate (ESR) in 18 (56.3%) patients with a mean ESR of 39.89 ± 23.37 mm/h (normal 0–20 mm/h). In the remaining patients, ESR was within the normal limits. The C-reactive protein (CRP) was reportedly positive in 13 (40.6%) patients, and in the remaining 19 (59.4%) patients, CRP was negative. In the majority of 25 (78.1%) patients, the anti-thyroid peroxidase (TPO) antibody level was normal with a mean level of 10.44 ± 9.30 IU/ml (normal 0–35 IU/ml). The Tg levels were normal in 17 (53.1%) patients and elevated in 14 (43.8%) patients. Similarly, the anti-Tg levels were normal and elevated in identical number of patients. The 15-min Tc-99m pertechnetate thyroid uptake levels [Table 5] were decreased in all (100%) patients at presentation in the range of 0.10%–0.3% with a mean uptake of 0.21% ± 0.06% (normal 0.4%–7.1%). The neck ultrasonography [Table 1] revealed hypoechoic lesions in 15 (46.9%) patients, normal study in 12 (37.5%) patients, nodules in 3 (9.4%), and subcentrimetric nodes in 2 (6.3%) patients. HLA-B35 testing [Figure 1 and Table 6] was done in 18 patients (females 16 and males 2). Ten (55.5%) patients that included 9 female patients and 1 male patient tested positive and 8 (45.5%) patients tested negative. No familial trends in SAT were observed among those who tested positive.

Table 1

Physical characteristics, symptoms, and ultrasonography findings

Table 2

Thyroid-stimulating hormone* profile of the study group at presentation, 3 months, 6 months, and 1 year

Table 3

Free thyroxine* profile of the study group at presentation, 3 months, 6 months, and 1 year

Table 4

Laboratory investigations in study participants at presentation

Table 5

Technetium-99m thyroid uptake* profile of the study group at presentation, 3 months, 6 months, and 1 year

Figure 1

Human leukocyte antigen-B35 testing

Table 6

Human leukocyte antigen-B35 association in subacute thyroiditis

At 3 months after presentation

Seven patients were lost to follow-up at 3 months. Tc-99m thyroid uptakes normalized in 14 (56%) patients with mean uptakes of 4.85 ± 1.23%. There was a rebound increase of uptakes in 11 (44%) patients with a mean uptake level of 10.95 ± 2.66%. No patients persisted with decreased thyroid uptakes observed at presentation. The overall thyroid uptakes in the study group at 3 months were on the higher side with mean uptake level 7.35 ± 3.65% (range: 2.6%–15.8%). The serum TSH levels were increased to normal in 15 (60%) patients with mean level of 4.97 ± 1.38 μIU/ml. An above the normal increase in TSH levels was observed in 10 (40%) patients with mean level of 8.01 ± 1.68 μIU/ml. None of the patients persisted with decreased TSH levels observed at initial presentation. The overall mean TSH level of 6.18 ± 2.11 (range: 2.28–12.37 μIU/ml) were elevated at 3 months. A scatter plot graph [Figure 2] between Tc-99m thyroid uptakes and serum TSH levels revealed a linear relationship (r = 0.54, P < 0.05).

Figure 2

Scatter plot of Tc-99m and TSH at 3 months

At 6 months after presentation

A total of 9 patients were lost to follow-up at 6 months. Tc-99m thyroid uptakes normalized in 22 (95.6%) patients with mean uptake of 4.79 ± 1.84%. Only 1 patient (4.4%) persisted with elevated uptake. The overall mean uptake in the study group at 6 months was 5 ± 2.11% (range: 1.2%–10.1%). The serum TSH levels were within normal limits in 21 (91.3%) patients with a mean level of 4.92 ± 1.25 μIU/ml. The serum TSH levels were elevated in 2 (8.7%) patients with a mean level of 6.65 ± 0.0 μIU/ml. The overall mean TSH level in the study group was 5.36 ± 1.39 μIU/ml (range: 3.81–6.66 μIU/ml) [Figures 2 and 3].

Figure 3

Graphic plot of thyroid function parameters

At 12 months after presentation

At 1 year, all the 23 (100%) patients who completed the study had normal Tc-99m thyroid uptakes with a mean uptake of 4.17 ± 1.8%. The serum TSH levels also normalized in all the 23 (100%) patients with a mean TSH of 4.93 ± 1.29 μIU/ml [Figures 2 and 3].

On an overall review of the results, SAT seems to commonly affect the younger population in the fourth decade of life and is more common among the female population. The common presenting symptoms of neck pain, easy fatigability, excessive sweating, fever, sore throat, and tremors reflect symptomatology of thyrotoxicosis precipitated by a viral infection causing disruption of thyroid follicles with a subsequent surge in ambient blood thyroxin levels. Tc-99m thyroid uptakes in SAT normalized in 56% of the patients within 3 months of presentation, in 95.6% of patients within 6 months, and in 100% by 12 months. The FT4 levels which were elevated in 90.6% of patients at presentation normalized in 56% of patients by 3 months, in 91.3% of patients by 6 months, and in 100% by 1 year [Figure 3]. The thyroid functional parameters are recovered by 3 months and are nearly normal by 6 months and completely normalized by 12 months. The HLA-B35 positivity was observed in 45.5% of patients, and no familial trends were observed in the study group. The discrepancies/improvement in the functional parameters at various stages in the natural evolution of SAT was found to be statistically significant when compared to the levels seen at presentation.

Discussion

SAT, a self-limiting inflammatory disorder of the thyroid gland owing to its symptomatology, has often been to the novice a diagnostic dilemma resulting in a delayed and sometimes over treatment which otherwise would need NSAID with reassurance and very rarely steroids. The diagnostic problem gets compounded by the stage at which a patient may report to a physician owing to the natural history of this disorder which usually over a period of few months progresses from an overt thyrotoxic state to a normal euthyroid state and very rarely to an occult hypothyroid state. The disorder like many other thyroid diseases predominantly affects women in a relatively younger age usually in the third to fourth decade. Genetic predisposition with familial trends in some studies has been documented in the literature albeit scantily.[3] Radionuclide usually I-131 and iodine-123 thyroid uptakes continues to be the confirmatory diagnostic procedure in most of the patients showing very low or no thyroid uptake in a setting of high blood levels of thyroxine and a transitory thyrotoxic state. Considering the increased referrals to our department of patients clinically suspected to have SAT, we undertook a pilot follow-up study of SAT with readily available Tc-99m thyroid scintigraphy. Of the 32 patients of SAT enrolled in our study, predominant 23 were females with a female-to-male ratio of 2.5:1 which was similar to the cohort Olmsted County and Minnesota study published by Fatourechi et al. in 2003 though their female-to-male ratio of 3.5:1 was slightly higher.[10] The mean age at presentation of 36.96 ± 12.17 years in the present study is more or less similar to 37.96 ± 8.5, 41.2 ± 11.2, and 37.2 ± 12.4 years in other published studies by Barhua et al.,[11] Mahar et al.,[12] and Kalra et al.,[13] respectively, though most of them like our study are based on Asian population. The mean age of 46 years at presentation from the published western data of Minnesota in the US is higher.[10] The main presenting symptoms of neck pain, easy fatigability, palpitations, sweating, and heat intolerance in the present study are more or less in concordance with previous published studies of Das,[14] Nishihara et al.,[15] and Mahar et al.[12] A history of sore throat seen in 56.3% of our patients was at variance with 26.9% of Mahar et al.[12] but similar to 68.7% of Nishihara et al.[15] ESR and CRP levels, markers of acute inflammation, were relatively lower in our study when compared to 90%–100% elevated levels in studies of Das,[14] Hamburger et al.,[16] and Baruah et al.[11] We attribute this unusual feature in our patients to reporting later in the acute phase of the disease. Expectedly, the lower mean TSH and higher mean FT4 levels were reported in an overwhelming majority of patients in this study, and this was in conformity with previous published studies of Benbassat et al.,[17] Qari et al.,[18] and Mahar et al.[12] An elevated Tg and anti-Tg levels of approximately 43% of patients were slightly lower than 72% of Gonza'lez Espinoza et al.[19] We attribute this to probable discordance in the presentation time among patients in the two studies. Only 6 (19.4%) patients had elevated anti-TPO levels in the present study suggesting a nonautoimmune insult of the thyroid. Our observation is shared by Gonza'lez Espinoza[19] who quoted elevated anti-TPO levels in only 3 out of 22 patients in his study. Predominant hypoechoic lesions of the thyroid on USG reported by Tachibana et al.[20] and Frates et al.[21] were seen in only 46.9% of patients in this study. The disparity in USG findings may be due to subjective errors and omissions in interpreting USG which is an accepted fallacy of the technology. Owing to cost constraints, HLA-B35 was tested in only 18 patients in this study. A majority of 10 (55.5%) patients were reported positive for HLA-B35 expression. A high positivity of HLA-B35 typing in the study group is a reason strong enough to believe in its role of conferring genetic susceptibility to SAT in the local ethnic population mostly triggered by a viral infection. Nevertheless, HLA-B35 typing may be recommended to patients only if their family members also have SAT to further understand its role in pathogenesis. HLA-B35 typing needs not be done in nonfamilial SAT since the result hardly affects the course and prognosis of the disease. A similar higher HLA-B35 positivity of 72% has been quoted in the published literature.[3] The relatively lower positivity rate in the present study can be attributed to a smaller number of patients undergoing this investigation. In the present study in a majority of patients, the thyroid functional parameters and thyroid Tc-99m uptakes reverted to normal within 6 months of presentation. The present study is unique in having used serial Tc-99m thyroid scintigraphy in patients of SAT for almost up to 1-year postdiagnosis and documented incremental improvement during the natural course of the disease.

Conclusion

The study based on an ethnic population from the northern mountainous region of India shows SAT most likely a nonautoimmune transitory inflammation of the thyroid gland to be common among females in their fourth decade of life. It usually follows a respiratory infection. Most of the patients of SAT present with usual symptoms of neck pain, easy fatigability, sore throat, heat intolerance, palpitations, and fever with elevated FT4. Markedly subnormal Tc-99m thyroid uptakes are as useful as I-131 thyroid uptakes to clinch the diagnosis and differentiate it from hyperthyroidism. HLA-B35 levels are elevated in a majority of patients suggesting its role in genetic susceptibility to SAT triggered by a viral infection. HLA-B35 typing may be done in family clusters of SAT to understand its role since the data on this aspect of SAT are scant. The thyroid starts reverting from its inflammatory insult as shown in this study from 3 months after the onset, and most of the patients recover completely by 6–12 months. It is a self-limiting disorder. An early diagnosis is the key to management which mostly requires reassurance and NSAID.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.