Year : 2010 | Volume
: 53 | Issue : 3 | Page : 476--479
Significance of eosinophils in diagnosing Hashimoto's thyroiditis on fine-needle aspiration cytology
Maheswari Ekambaram1, Bipin Kumar2, Nitlotpal Chowdhary2, N Siddaraju2, Surendra Kumar2,
1 Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India
2 Department of Pathology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India
Department of Pathology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry
Background: Hashimoto«SQ»s thyroiditis (HT) is the most common cause of hypothyroidism in those areas of the world where iodine levels are sufficient. Fine-needle aspiration cytology (FNAC) can accurately diagnose this lesion in most of the patients. However, a small percentage of cases may be missed due to inherent limitations of this procedure. Therefore, cytologic clues to increase sensitivity of diagnosis need to be searched for. Aims: To assess whether an eosinophilic infiltration of the thyroid gland has a higher association with HT than colloid goiter. Materials and Methods: The study was a case-control study. Smears obtained by FNAC of 50 case, each of HT (which served as cases) and colloid goiter (which served as controls) were observed. The number of eosinophils and neutrophils per high-power field (HPF) was counted in all the smears. The eosinophil-neutrophil ratio in the smears, diagnosed as HT, was then compared with that of colloid goiter using unpaired t-test. Results: Smears diagnosed as HT was found to have a significantly higher eosinophil-neutrophil ratio than smears diagnosed as colloid goiter (P value 0.0001). Conclusion: Eosinophilic infiltration of the thyroid gland has higher association with Hashimoto thyroiditis.
|How to cite this article:|
Ekambaram M, Kumar B, Chowdhary N, Siddaraju N, Kumar S. Significance of eosinophils in diagnosing Hashimoto's thyroiditis on fine-needle aspiration cytology.Indian J Pathol Microbiol 2010;53:476-479
|How to cite this URL:|
Ekambaram M, Kumar B, Chowdhary N, Siddaraju N, Kumar S. Significance of eosinophils in diagnosing Hashimoto's thyroiditis on fine-needle aspiration cytology. Indian J Pathol Microbiol [serial online] 2010 [cited 2020 Jul 5 ];53:476-479
Available from: http://www.ijpmonline.org/text.asp?2010/53/3/476/68282
Hashimoto's thyroiditis (HT) also known as chronic lymphocytic thyroiditis has a prevalence rate of 1-4% and incidence of 3-6/10000 population per year.  It is the second most common thyroid lesion diagnosed by cytology, after endemic goiter.  This disorder is more common in women than in men. Patients usually present with a diffuse enlargement of the thyroid gland or less frequently with one or two prominent nodules.  In the usual clinical course, hypothyroidism develops gradually. 
Fine-needle aspiration cytology (FNAC) is highly sensitive in diagnosing HT, with a diagnostic accuracy rate of 92%.  Hashimoto's thyroiditis is diagnosed on FNAC smears by finding the Oxyphilic (Hurthle) cells, infiltration of follicles by lymphocytes and plasma cells and the presence of moderate number of it in the background. Fine-needle aspiration cytology reliably distinguishes between colloid goiter and autoimmune thyroiditis in most cases, which is important, as the latter requires lifelong follow-up or treatment with thyroxine to avoid subtle decline into hypothyroidism.  Fine-needle aspiration cytology is considered superior as well as more cost-effective in diagnosing HT than antibody screening. ,, However, there are certain pitfalls of FNAC in diagnosing HT. Diagnosis of HT is likely to be missed in smears showing cytological evidence of hyperplasia or abundant colloid.  Lymphocytic infiltration of the gland in Graves' disease may result in an overlap of cytological appearances with HT.  Follicular cells that exhibit some of the features of papillary carcinoma, such as nuclear enlargement, nuclear crowding, nuclear inclusion and nuclear groove could be observed in a cytology smear of HT, leading to a diagnostic pitfall.  A minimal lymphoid population in the background can be seen in endemic goiter, which can again be confused with HT. 
We observed thyroid tissue eosinophilia in many of the FNAC smears that were diagnosed as HT. This prompted us to undertake this study to assess if there was a significant association between eosinophilic infiltration of the thyroid gland and HT.
Materials and Methods
This was a case-control study. The study was done between the periods of May and October 2005. Aspiration was done with 23-gauge needle and 10 ml of disposable plastic syringe. The smears were alcohol fixed, air dried and stained with Papanicolaou stain and May-Grόnwald-Giemsa stain. The diagnosis of HT was confirmed by finding lymphocytic infiltrates in clusters of follicular epithelial cells, Hurthle cell changes and increased number of lymphocytes in the background and of colloid goiter by the presence of cohesive monolayer sheets or poorly cohesive clusters of follicular epithelial cells, bare nuclei, macrophages and abundant colloid. Fine-needle aspiration cytology (FNAC) smears confirmed as HT and colloid goiter were studied. Smears obtained by FNAC of 50 consecutive diagnosed cases of HT served as cases while smears of 50 consecutive diagnosed cases of colloid goiter served as controls. The number of eosinophils per high-power field (HPF) was counted in both cases as well as control smears. The eosinophils were recognized by their bi-lobed nucleus and reddish orange, spherical, coarse cytoplasmic granules. The number of neutrophils per HPF was also counted to eliminate eosinophilia due to admixture with blood. At least ten fields were checked in all the smears and the average calculated. The ratio of eosinophils to neutrophils in the smears diagnosed as HT and in the smears diagnosed as colloid goiter was tabulated. The difference between the two observations was statistically analyzed.
We observed eosinophilic infiltration in thyroid tissue in many of the FNAC smears that were diagnosed as HT [Figure 1],[Figure 2],[Figure 3]. Number of eosinophils per HPF in the smears diagnosed as HT was found higher than in the smears diagnosed as colloid goiter [Table 1]. Average number of eosinophils and neutrophils per HPF was found more in the smears diagnosed as HT than in the smears diagnosed as colloid goiter [Figure 4]. The ratio of eosinophils to neutrophils in the smears diagnosed as HT was found to be significantly greater than in smears diagnosed as colloid goiter [Table 2]. The findings were analyzed using unpaired t-test (SPSS software for Windows - version 15.0). On applying the test, the P-value was 0.0001 with a 95% confidence interval (0.21, 0.44). Thus, eosinophilic infiltration of the thyroid had higher association with HT than with colloid goiter.
Hashimoto's thyroiditis is an autoimmune chronic inflammatory disease of the thyroid gland.  The incidence of HT seems to be increasing in the recent times. In a study conducted by Marwaha et al, among 764 girls with thyroid enlargement, 5.6% of them were diagnosed to have HT on the basis of FNAC.  A study conducted by Benvenga et al, has shown that HT has become 10 times more common than it was until the early 1990s.  Another study conducted by Zois et al, among school children in 2003 had shown a three-fold increase in the incidence of autoimmune thyroiditis compared to a similar survey done seven years earlier.  This increase in incidence has been linked to excess iodine intake particularly in the coastal areas. ,,,,,
It is important to diagnose HT because patients can become hypothyroid, which will need lifelong thyroxine supplementation. Also, there is an increased risk of extranodal marginal B-cell lymphoma in patients with HT. The frequency of carcinoma in patients with HT varies between 0.5 and 23.7%.  This emphasizes the need for diagnosing HT so that patients can be on long-term follow-up. In the present study, T3, T4 and TSH levels were estimated in both cases as well as controls. In the case group, 3 cases were found hyperthyroid suggesting Hashitotoxicosis, 5 cases were euthyroid and remaining 42 cases were hypothyroid. All controls were euthyroid.
Antithyroglobulin and/or antimicrosomal antibodies are positive only in 60-80% of cases of HT and 10-15% of patients with positive antibodies may not have thyroiditis. ,, In the present study, the antibodies estimation were done in 40 cases and 8 controls, out of which 26 cases and 3 controls were found to be positive. Thus, cases may be missed or sometimes over-diagnosed, if antibody estimation is used as the sole screening indicator of the disease.  Therefore, in a proper clinical setting, the diagnosis of HT may be considered on cytological evidence alone even if antibody titers are negative. 
Despite its superiority, FNAC has some pitfalls in diagnosing HT. There is sometimes an overlap in the cytomorphological features of HT and sub-acute lymphocytic thyroiditis.  The diagnosis can also be missed in smears with abundant colloid. 
Our study has shown a significant infiltration of the thyroid gland with eosinophils in case of HT than in cases with colloid goiter. This eosinophilic infiltration was observed in lymphoid aggregate, thus ruling out admixture with blood. This is a finding that has rarely been reported.  We propose that eosinophilic infiltration of the thyroid gland is highly associated with HT on FNAC. Few animal studies, which report a similar finding, are also found. , In a study conducted by Cohen et al, guinea pigs were immunized with thyroid extracts in complete Freund's adjuvant to induce thyroiditis. Thyroid lesions, consisting of focal lymphoid infiltrates, occurred in the presence or absence of detectable circulating antithyroid antibody. Eosinophils were found only in the thyroids of those animals, which have, both thyroid lesions and antibody activity. When present, they were located in close proximity to small blood vessels, and in large numbers in the fibro-fatty tissue surrounding the gland. The local accumulation of eosinophils appears to be related to the presence of both lymphocytes in the thyroid and circulating antibody, suggesting that the lymphocyte-derived eosinophil chemotactic factor might be involved in this accumulation. 
In another study conducted by Sharp et al, guinea pigs that received a passive transfer of rabbit antiserum to guinea pig thyroglobulin developed an eosinophilic infiltrate of the thyroid. The infiltration varied in intensity in different guinea pigs, developed over a 1-24-h period, and resolved in 4-9 days. The study proposed that thyroglobulin is also present in the interstitial areas either normally or as a result of the antiserum injection and that the eosinophils appeared in response to the presence of thyroglobulin-antithyroglobulin complexes in these areas. 
Not only has iodine-induced thyroiditis increased in prevalence, the histological features of chronic lymphocytic thyroiditis has also changed to a certain degree. , Eosinophilic infiltration of the thyroid gland may reflect one such change.
Hence, we conclude that eosinophilic infiltration of the thyroid gland has higher association with Hashimoto thyroiditis. We sincerely hope that further larger and independent studies will help us in understanding the significance of eosinophilic infiltration of the thyroid gland in cases of Hashimoto's thyroiditis.
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