the differential diagnosis of predominant plasmacytoid cells on thyroid fine - needle aspirates should also include ptl with extensive plasmacytic differentiation , besides plasmacytoma .
further studies are required to assess plasmacytic differentiation in various thyroid lymphomas so as to differentiate them from plasmacytomas , the two entities having a different line of management .
primary thyroid gland lymphomas ( ptls ) are uncommon tumors that have been estimated to represent approximately 5% of all thyroid neoplasms and 2.5 - 7% of all extranodal lymphomas .
studies have shown that ptls typically occur in middle - to older - aged women and arise in the setting of autoimmune thyroiditis ( lymphocytic thyroiditis , hashimoto 's disease ) . the term 
primary designates patients with lymphomatous involvement of the thyroid at diagnosis , the disease being localized or disseminated to nodal or extranodal sites .
patients present with a mass in the thyroid , usually noticeably enlarging , and commonly have symptoms related to compression of neck structures by the tumor .
with radioisotopic i scanning , a cold nodule or areas of decreased uptake are common .
( dlbcl ) and mucosa - associated lymphoid tissue lymphoma ( malt ) are the two most common histologic subtypes of ptl .
small lymphocytic b - cell lymphoma ( sll ) is an extremely rare type of thyroid lymphoma ( about 4% of cases ) .
cervical lymph nodes are the most frequently involved site , followed by a variety of other nodal and extranodal sites , including mediastinal lymph nodes , gastrointestinal tract , bone marrow , lung , bladder , liver , and spleen .
chronic lymphocytic leukemia / small lymphocytic lymphoma ( cll / sll ) presenting initially as a thyroid abnormality is extremely rare , with very few reported cases in the literature .
a 60-year - old postmenopausal female presented with swelling involving the midline of the neck measuring 6 cm in largest dimension for the past 1 month .
she also had an enlarged lymph node of 1.5 cm diameter in the left cervical region .
routine laboratory tests were normal and hormonal evaluation showed subclinical hypothyroidism ( serum thyroid - stimulating hormone ( tsh ) , 12.8 iu / ml ( normal range 0.25 - 5.25 iu / ml ) ; free t3 and free t4 were within normal range ) .
cytological examination of thyroid and left cervical lymph node obtained during fine - needle aspiration revealed a similar appearance with a predominant cell population of small - to medium - sized cells revealing paracentral to eccentric nuclei with clock - face chromatin and abundant sky - blue cytoplasm along with few hurthle cells ( fig . 1 , 2 ) .
a provisional diagnosis of lymphoma / plasmacytoma was made and patient was advised immunoelectrophoretic studies and skeletal imaging for confirmation , however all turned out to be normal . subsequently , a biopsy was performed from cervical lymph node .
histopathological and immunohistochemistry findings in the specimen led to the diagnosis of small lymphocytic b - cell lymphoma ( sll cd20 + , cd19 + , cd5 + , cd23 + , + , - ) ( fig .
3 ) . to confirm thyroid involvement , flow cytometry of the biopsy material sampled from the thyroid was performed showing b - cell immunophenotype with plasma cell differentiation : cd19+/cd20 + , cd23+/cd5 + , scd79b-+ , cd38 + , cd10- , + and -/weak reaction .
staging procedures including peripheral blood and bone marrow examination , ct scan of thorax , abdomen and pelvis did not reveal any other involvement .
the patient was started on chemotherapy according to a cop ( cyclophosphamide , vincristine and prednisolone ) regimen with good response and is still under follow - up .
ptl , with an estimated annual incidence of 2 cases per million , is a rare thyroid malignancy .
the most common clinical presentation is a rapidly growing neck mass , which is reported in 70% of patients , whereas compression symptoms and signs are present in 30% and b symptoms are reported in 10% of patients .
cervical / perithyroidal lymph nodes were the most common nodal sites involved , usually identified at , or shortly after initial surgery , followed by mediastinal and abdominal lymph nodes .
malt is the second most common subtype , and sll is one of the rarest .
a vast majority of cases of ptl arise in the setting of hashimoto 's thyroiditis .
it is estimated that the relative risk of developing a thyroid lymphoma is increased 67-to 80-fold in patients with hashimoto 's thyroiditis .
the few cases ( < 7% ) that did not have documented lymphocytic thyroiditis may have been either inadequately sampled or the lymphoma may have completely obliterated any residual thyroid tissue .
the initial diagnostic method for thyroid lymphoma should consist of a fine - needle aspiration biopsy with the use of ancillary techniques such as flow cytometry and immunohistochemistry for improved diagnostic accuracy .
cll / sll is one of the rarest subtypes of lymphoma that can involve the thyroid gland .
diagnosis of this entity is difficult , particularly before the recognition of systemic involvement , requiring the expertise of a multidisciplinary team for early detection and optimal management .
the cases previously reported in various studies as extramedullary plasmacytomas of the thyroid represented marginal zone b - cell lymphoma ( mzbl ) with extreme plasma cell differentiation .
overall , ptls have a favorable outcome with appropriate therapy , but prognosis depends on both clinical stage and histology .
mzbl and stage ie tumors have an excellent prognosis , whereas tumors with a large cell component or dlbcl or stage greater than ie have the greatest potential for a poor outcome .
the treatment of primary lymphomas of the thyroid gland , as well as infiltration changes associated with cll / sll , remains controversial .
the recommended strategy includes chemotherapy , radiotherapy , and in particular cases also surgery and immunochemotherapy with monoclonal antibodies .
it should be emphasized that the diagnosis of ptl based on fine - needle aspiration biopsy is not always possible with extensive plasmacytic differentiation posing a major diagnostic problem .
further studies are required to assess plasmacytic differentiation in various thyroid lymphomas so as to differentiate them from plasmacytoma  the two entities having a different line of management and prognosis .
the authors declare that no financial or other conflicts of interest exist in relation to the content of the article .
 primary thyroid gland lymphomas ( ptls ) typically occur in middle - to older - aged individuals in the setting of lymphocytic thyroiditis with a predilection for females . diffuse large b - cell lymphoma is the most frequent histologic subtype of thyroid lymphomas . 
 small lymphocytic lymphoma ( sll ) belongs to the least common subtypes of thyroid lymphoma . 
 it is often associated with the involvement of lymph nodes , bone marrow , spleen , liver and , extremely rarely , other organs . 
 ptls with plasmacytic differentiation or extensive infiltration by plasma cells have been observed in marginal zone b - cell lymphomas in the thyroid but have never been described in a setting of sll . 
 here , we present a case of primary sll of the thyroid mimicking extramedullary plasmacytoma on fine - needle aspiration cytology . 
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