Indian Journal of Pathology and Microbiology

ORIGINAL ARTICLE
Year
: 2011  |  Volume : 54  |  Issue : 3  |  Page : 464--471

Histopathologic and immunohistochemical features of Hashimoto thyroiditis


H Kazem Amani 
 Department of Pathology, Medical Research Institute, Alexandria University, Egypt

Correspondence Address:
H Kazem Amani
Deaprtment of Pathology, Medical Research Institute, Alexandria University, 67, Omar Loutfi Street, Alexandria
Egypt

Abstract

Background: Intrathyroid lymphoid tissue is accrued in Hashimoto thyroiditis (HT). Histologically, this acquired lymphoid tissue bears a close resemblance to mucosa-associated lymphoid tissue (MALT) and can evolve to lymphoma. Aim: To demonstrate the morphological, and immunohistochemical profiles of Hashimoto thyroiditis and to ascertain the importance of light chain restriction in distinguishing HT with extensive lymphoplasmacytoid infiltrate from MALT lymphoma. Materials and Methods: We studied histopathologically and immunohistochemically (CD20, CD3, Igk, Igl and cytokeratin) 30 cases of HT for evaluation of the lymphoid infiltrate and the presence of lymphoepithelial lesions (LELs). Distinguishing between early thyroid lymphoma and HT was evaluated by light chain restriction. These findings were compared with two cases of primary thyroid lymphoma. Results: The histopathological findings were characteristic of HT. Immunohistochemistry confirmed inconspicuous, rare B-cell LELs as well as a prominent T-lymphocyte population. Testing for light chain restriction showed polyclonal population of plasma cells. The cases of MALT lymphoma had distinct destructive lymphoepithelial lesions, B-cell immunophenotyping and showed kappa light chain restriction in the plasmacytoid population. Conclusions: Hashimoto thyroiditis differs both histopathologically and immunohistochemically from thyroid lymphoma. In suspicious cases, immunohistochemistry could be helpful in reaching a definitive diagnosis.



How to cite this article:
Amani H K. Histopathologic and immunohistochemical features of Hashimoto thyroiditis.Indian J Pathol Microbiol 2011;54:464-471


How to cite this URL:
Amani H K. Histopathologic and immunohistochemical features of Hashimoto thyroiditis. Indian J Pathol Microbiol [serial online] 2011 [cited 2019 Aug 19 ];54:464-471
Available from: http://www.ijpmonline.org/text.asp?2011/54/3/464/85076


Full Text

 

Introduction



Several studies have linked certain autoimmune and chronic inflammatory conditions to an increased occurrence of lymphoma. [1] However, the magnitude of the average lymphoma risk increase in each disorder varies considerably among studies. [2] It is well known that almost all thyroid lymphomas arise in the setting of Hashimoto thyroiditis (HT), which induces reactive lymphoid proliferation leading to the development of mucosa-associated lymphoid tissue (MALT) lymphoma, which can lead to an aggressive lymphoma. [3],[4],[5],[6],[7],[8],[9]

We need to learn how to identify individuals who are at substantially increased lymphoma risk and how to intervene against this risk. [10]

The coexistence of reactive and neoplastic processes in the thyroid may cause difficulty in diagnosing mucosa associated lymphoid tissue lymphoma (MALTOMA) using cytology or histology. This has led to the use of immunohistochemistry and molecular techniques to confirm or exclude the diagnosis. [11]

The aims of our study were to demonstrate the morphological and immunohistochemical profiles of HT, and to ascertain the importance of clonality in distinguishing HT from MALT lymphoma.

We used morphology and immunohistochemistry to study 30 cases of HT. Clonality was assessed by immunostaining for kappa (k) and lambda (l) light chains of immunoglobulins (Ig). The findings were compared with two cases of primary thyroid lymphoma.

 Materials and Methods



Specimens

The present study was performed on 32 thyroidectomy specimens corresponding to 30 cases of HT and two cases of primary thyroid non-Hodgkin's lymphoma, received at the Pathology Department of the Medical Research Institute, Alexandria University, Egypt. The procedures followed in the study were in accordance with the ethical standards of the Medical Research Institute committee on human experimentation.

Formalin-fixed, paraffin-embedded 3 to 4-mm tissue sections were prepared from each case and stained routinely by hematoxylin and eosin (H and E) stain for histopathologic diagnosis and evaluation of the lymphoid infiltrate, and the presence of lymphoepithelial lesions (LELs). Lymphoepithelial lesions were defined as clusters of three or more lymphocytes in the glandular epithelium.

Immunohistochemistry

Further sections on coated slides were prepared for immunohistochemical staining using avidin biotin peroxidase complex method. [12] Briefly, after the inhibition of endogenous peroxidases with 3% hydrogen peroxide, slides were treated by microwave in 10mM citrate buffer for 15 min. After washing the slides in Tris-Buffer saline (TBS), they were incubated with 10% normal goat serum at 23°C for 30 min. Slides were then incubated at 4°C overnight with the following primary antibodies: CD20 (L-26), CD3, Igk, Igl and anti-cytokeratin antibody (AE1/AE3) (Dako, Denmark).

The incubation was followed by addition of biotin-conjugated goat anti-mouse, anti-rabbit IgG diluted 1:200 for 20 min. A final 45-min incubation with streptavidin-conjugated horseradish peroxidase diluted 1:200 in TBS was performed. The reaction product was developed for 5 min with diaminobenzidine tetrahydrochloride (DAB) and the sections were lightly counterstained with Mayer's Hematoxylin.

Monoclonality is assumed when there is a ratio of 10:1 or greater between [kappa] and [lambda] staining cells. [13]

 Results



A summary of the clinicopathologic characteristics is shown in [Table 1].{Table 1}

Clinical Findings

The present study was undertaken on 30 cases of HT. Twenty-five patients were females. The mean age at diagnosis was 44.63 years (range, 15-70 years). All patients presented with goiter (18 cases diffuse and 12 nodular) of average size 3.7 cm. Two female patients aged 65 and 80 years with primary thyroid lymphoma were included as a control, they presented with a rapidly growing fixed nodular goiter (6 x 5 x 4 cm) and (8 x 5 x 3 cm), extending beyond the thyroid with clinical consequences such as pressure symptoms in the neck and dyspnea.

Histopathological Findings

Hashimoto thyroiditis

All cases showed classic features of HT; a lymphoid infiltrate arranged in lymphoid follicles with interfollicular small round lymphocytes, plasma cells, scattered lymphoplasmacytoid cells, and a few large transformed cells [Figure 1]a and b. Most lymphoid follicles had a well-defined germinal centre and mantle zone with absent marginal zone. An extensive lymphoplasmacytoid infiltrate with focal effacement of architecture by atypical cells was seen in two cases with atrophy of thyroid follicles [Figure 1]c. Hurthle cell metaplasia was a constant feature [Figure 1]d. Lymphoepithelial-like lesions were rarely seen [Figure 1]e.{Figure 1}

Primary thyroid lymphoma

In the cases of primary thyroid lymphoma, the parenchyma was diffusely replaced by a dense, atypical lymphoproliferative infiltrate, composed of monocytoid lymphocytes with small, slightly irregular folded or centrocyte-like nuclear contours, condensed nuclear chromatin, inconspicuous nucleoli, and abundant pale cytoplasm [Figure 2]a. The lymphoepithelial lesions were frequent [Figure 2]b. An admixture of lymphoplasmacytoid cells having abundant, eccentrically placed brightly eosinophilic cytoplasm was identified. Residual thyroid epithelium was present in the lymphoid infiltrate; this took the form of small follicles containing colloid or of small acinar structures without colloid. The capsule was invaded as well as the adjacent adipose tissue and skeletal muscles.{Figure 2}

Immunohistochemical Findings

Hashimoto thyroiditis : Was composed of numerous small lymphocytes (a mixture of T and B-cells, but often with a predominance of T-cells). Most of the lymphoid infiltrate in HT was arranged as lymphoid follicles composed of B-cells (CD20+, CD3-) [Figure 3]a. The interfollicular lymphoid infiltrate was composed predominantly of T-cells (CD3+, CD20-) admixed with a very small number of B-cells and plasma cells [Figure 3]b-e. In the scant lymphoepithelial lesions seen, the invading lymphocytes were T-cells (CD3+) [Figure 3]f. Cytokeratin demonstrated the preserved thyroid follicles [Figure 3]g. The two lymphocyte rich thyroiditis cases showed increase in CD20-positive lymphocytes with well-circumscribed germinal centers surrounded by mantle zone. The follicles were connected by interfollicular dense lymphoid infiltrate widely separating the follicular acini [Figure 3]h. However, the lymphoid population was polyclonal as evidenced by dual positivity for k and l immunostaining. In these polyclonal infiltrates, the lambda/kappa ratio never exceeded 1:5. [Figure 4]a and b.{Figure 3}{Figure 4}

Primary thyroid lymphoma: The two cases of MALT lymphoma were characterized by predominance of B-cells that were not confined to germinal centers. The small and large neoplastic cells in the marginal zone and in the diffuse areas expressed CD20, and were negative for CD3 confirming B-cell lineage [Figure 2]c and d. Rare intact thyroid follicles were identified due to the abundance of destructive lymphoepithelial lesions [Figure 2]e. These lymphoepithelial lesions were more numerous than in HT cases and showed prominent follicular stuffing, with focal packing of follicular lumina by centrocyte-like lymphoid cells [Figure 2]f. Cytokeratin decorated the residual atrophic thyroid follicular elements [Figure 2]g and h. Immunostaining for k and l confirmed the morphologic diagnosis, where the lymphoid population was clear-cut monoclonal for k with at least a 10:1 ratio, counted in 10 high-power fields [Figure 4]c and d.

 Discussion



Hashimoto thyroiditis is an established risk factor for the development of lymphoma in the thyroid. [4] These patients have a threefold excess risk of developing lymphoma, and an 80 fold increased risk of thyroid lymphoma (the overall lymphoma risk is 0.1% of patients). [3] Indeed, lymphocytic thyroiditis is present in the background in 94% of thyroid lymphomas. [14] Even if endocrinologists are aware of the increased risk of lymphoma in these pathologies, diagnosis of thyroid lymphoma remains difficult because the clinical history, the physical examination, the thyroid function tests, and the ultrasound examination are not specific to detect the occurrence of lymphoproliferative disorders. Furthermore, it is sometimes difficult to recognize the low-grade lesions as distinct from lymphocytic thyroiditis. Distinguishing severe chronic lymphocytic thyroiditis from lymphoma can, at times, pose great difficulty. [15]

The present work was undertaken on 30 cases of HT in order to characterize them, both morphologically and by immunohistochemistry. Two cases of MALT thyroid lymphoma were studied in parallel by the same methods, in order to highlight and establish the difference between them. The aims of the work were to find the precise criteria that could enable us to differentiate between HT and early lymphoma. The second aim was to determine if monoclonal lymphoid population could occur in otherwise bland HT, as it can occur in Helicobacter pylori-associated gastritis and Sjφgren disease. [16],[17]

In this study, cases of HT were characterized by frequent lymphoid follicles with reactive wide germinal centers. The mantle zone was prominent and the interfollicular tissue was widened by a dense infiltrate of lymphocytes and plasma cells. The thyroid follicles showed atrophy and Hurthle cell metaplasia. Two cases showed partial effacement of the thyroid architecture by the lymphoid infiltrate with focal lymphoepithelial-like lesions; however, areas typical of HT often predominate. Similar findings have been reported in the literature, [18] where it was noted that thyroiditis can create an effacement of the normal thyroid follicular architecture, even with the formation of what could be classified as lymphoepithelial lesions. Several researches [18],[19] indicated that the germinal centers, often a prominent component of thyroiditis, can be scanty and appear over-run in some severe  cases.

A predominant reactive lymphoid population might mask an early lymphomatous transformation. On the other hand serologic markers such as lactic dehydrogenase (LDH) and ί 2 -microglobulin became significantly elevated only in advanced lymphomas. Therefore, a thyroid biopsy would be more appropriate in such a situation to reach the proper diagnosis. [20],[21]

In accord with others, [16],[22] all the cases of HT studied in this work showed an admixture of B and T-lymphocytes with the latter predominating. CD20 highlighted the germinal centers, while CD3 demonstrated the well-developed mantle zone as well as the interfollicular population. The cases showing apparent lymphoepithelial lesions were formed mainly of T-lymphocytes thus excluding MALT lymphoma. Cytokeratin was also done which indicated the rarity of destructive lymphoepithelial lesions in thyroiditis cases.

In the literature others have detected clonal B-cell proliferation in HT by several means (immunohistochemistry (IHC), southern blot hybridization, polymerase chain reaction (PCR), and PCR + sequencing). [5],[22],[23],[24],[25] Some explained the presence of such clones as a selective proliferation of a small number of B-cell clones as part of the autoimmune response in HT. [22],[26] Others confirmed that thyroid lymphomas do develop in patients previously diagnosed as HT. [27] Furthermore, D'Antonio et al.,[28] have reported the existence of a minute focus of extranodal marginal zone lymphoma about 4 mm in diameter in a case of HT, and recommended careful examination of thyroid specimens to disclose small foci of lymphomatous transformation.

In the present study two cases of HT showed focal effacement of architecture by atypical lymphocytes. Therefore, the possibility is raised that these cases might be harboring a clone that may later on develop into lymphoma. However, k and l immunostaining demonstrated polyclonal staining of lymphocytes, meaning that the infiltrating lymphocytes were a reactive proliferation, thus excluding the possibility of early lymphoma.

In accord with others, the two cases of MALT lymphoma included in this work were characterized by effacement of thyroid architecture by diffuse lymphoid infiltrate extending to extrathyroid tissues and the infiltrate mainly composed of monocytoid cells having cleaved nuclei and abundant clear cytoplasm. Admixed were plasmacytoid lymphocytes. [17],[21] Destructive LELs were abundant, completely replacing the thyroid follicles. The residual follicles were highlighted by anticytokeratin, CD20 was uniformly positive, whereas CD3 was negative, confirming the B-cell nature of lymphoma. Kappa and lambda immunostaining revealed strong homogenous positivity for k immunostaining and negative l immunostaining.

In conclusion, strict morphological and immunohistochemical criteria differentiate HT from MALT lymphoma. For morphologically borderline cases (florid lymphoid infiltrate), cytokeratin, CD20, CD3 in addition to k and l immunostaining could contribute in making the distinction.

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