13 July 2016 - Case of the Week #394

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Case of the Week #394

Clinical history:
A 71 year old man presented with a painless, right sided neck mass increasing in size for three months. He had mild dysphagia but was otherwise asymptomatic. Ultrasound revealed three hypoechoic thyroid nodules, all within the right lobe, measuring 4.2 cm, 3.0 cm and 1.0 cm. As fine needle aspiration was suspicious for neoplasia, he underwent a total thyroidectomy.


Gross description:
Gross examination showed 3 non encapsulated, well circumscribed white masses. No necrosis was seen.


Micro images:

10x

20x

40x




What is your diagnosis?































Diagnosis:
Solitary extramedullary plasmacytoma of the thyroid


Discussion:

Immunohistochemistry:
The neoplastic plasma cells were positive for CD138, CD79a and kappa light chain, but were negative for lambda light chain, as well as TTF1, thyroglobulin, synaptophysin, chromogranin and calcitonin.

CD79a

CD138

Kappa

Lambda



Micro description:
Plasma cell dyscrasias are separated into six distinct classes: plasmacytoma, multiple myeloma, lymphoplasmacytic lymphoma, heavy chain disease, primary or immunocyte associated amyloidosis and monoclonal gammopathy of undetermined significance (MGUS, Case Rep Otolaryngol 2012;2012:282784). Plasmacytoma is further divided into two subtypes, solitary plasmacytoma of the bone (SPB) and extramedullary plasmacytoma (EMP). EMP involves the soft tissue without systemic involvement (Blood Res 2014;49:280).

Solitary EMP is a rare neoplasm that occurs most frequently in the head and neck region, especially the upper aerodigestive tract. It occurs only rarely in the thyroid gland (Thyroid 2012;22:861, Acta Clin Belg 2015;70:133, J Cytol 2014;31:53). Avila et al., have documented a slight female predominance with a median age of 64 years (Ann Diagn Pathol 2009;13:119).

Specific diagnostic criteria for extramedullary plasmacytoma are required to ensure that multiple myeloma has been excluded. These include monoclonal plasma cell histology at tissue biopsy, plasma cell infiltration of less than 5% of all nucleated cells at bone marrow biopsy, a low serum M protein concentration, and the absence of osteolytic bone lesions, hypercalcemia, anemia and renal failure (Haematologica 2000;85:47).

Histopathology shows discohesive cells with few entrapped atrophic thyroid follicles. The neoplastic cells demonstrate plasma cell morphology, featuring eccentric, round nuclei with clumped, "cartwheel" chromatin and abundant basophilic cytoplasm with perinuclear clearing. Sporadic binucleated and multinucleated plasma cells may be noted. The thyroid parenchyma often shows significant lymphocytic infiltration with germinal centers (background of lymphocytic thyroiditis).

The histologic differential diagnosis includes thyroid medullary carcinoma, as well as involvement of the thyroid by multiple myeloma and plasma cell granuloma. Medullary carcinoma of the thyroid may present as a solid proliferation with plasmacytoid cells, but will have a different immunochemical profile (positive for synaptophysin, chromogranin and calcitonin, Diagn Cytopathol 2000;23:354). Differentiating EMP from secondary thyroid involvement by multiple myeloma requires additional clinical information (ScientificWorldJournal 2012;2012:895765). Similar to EMP, plasma cell granuloma may arise in a background of Hashimito thyroiditis, but unlike EMP, it is polyclonal on immunohistochemistry (Endocr Pract 2008;14:611).

The prognosis of extramedullary plasmacytoma is favorable. All sites included, the 10 year overall survival rate is 70%. Only 11% of cases progress to multiple myeloma over a 10 year period (Clin Oncol (R Coll Radiol) 2004;16:405).


Discussion edited by: Dr. Jennifer R. Kaley, University of Arkansas for Medical Sciences (USA).