Coexistence of leukemic infiltration and extramedullary hematopoeisis in a lymph node: A cytological diagnosis.

Extramedullary hematopoeisis (EMH) occurs when function of the bone marrow is insufficient or destroyed. We report a case of lymph nodal mass in a young patient, diagnosed on fine needle aspiration cytology (FNAC) as infiltration by leukemia along with features of EMH. FNA smears from axillary lymph node revealed lymphoblasts with hand mirror cell and teat cell morphology. Also seen were occasional megakaryocytes and metamyelocytes.

Introduction

In leukemia, infiltration of lymph nodes by leukemia cells can occur at any stage of the disease, i.e. during the course of leukemia, prior to onset of marrow leukemia or during relapse.[1] Extramedullary hematopoeisis (EMH) occurs when function of the bone marrow is insufficient or destroyed. Most commonly it occurs secondarily to a variety of hematological disorders such as myelofibrosis, thalassaemia and infiltrative disorders including lymphomas.[2] Involvement of lymph nodes by leukemia and EMH is known; however, to the best of our knowledge, occurrence of both in the same lymph node has not been reported. We report a case of a young patient detected on fine needle aspiration cytology (FNAC) to have infiltration by lymphoblasts as well as evidence of EMH in the same lymph node and the diagnostic difficulties it posed.

Case Report

A 19-year-old male patient presented with fever and weakness for 18 days. On examination, he was febrile, pale and had enlargement of bilateral cervical, left axillary and left inguinal lymph nodes. There was mild splenomegaly. All the lymph nodes were discrete, soft to firm and mobile, measuring 1–2 cm in size. The left axillary lymph node was 2 × 1 cm and tender on palpation. FNAC was performed using 23 G needle from the left cervical and left axillary lymph node by non-aspiration technique. Two smears were air dried for May-Grünwald-Giemsa (MGG) stain and one was wet fixed in alcohol for hematoxylin and eosin staining. Peripheral blood film (PBF) was also prepared.

Cytology findings

FNA smears from the left axillary lymph node showed predominantly immature lymphoid cells, two to three times the size of small lymphocytes with scanty cytoplasm conforming to morphology of lymphoblasts. Many hand mirror cells and teat cells were also present [Figure 1]. Also seen were occasional giant cells with multilobated nuclei and abundant cytoplasm, nucleated red blood cells (RBCs) and occasional metamyelocytes [Figure 2]. Background showed few mature lymphocytes and numerous lymphoglandular bodies. The left cervical lymph node aspirate smears showed mixed population of lymphoid cells in varying stages of maturation comprising follicle centre cells and mature lymphocytes. The PBF was examined keenly and showed decreased cell counts with 12% lymphoblasts and reduced platelets with normocytic normochromic red cells.

Figure 1

FNA smear from left axillary lymph node showing infiltration by lymphoblasts. Occasional mature lymphocytes are also seen (MGG, × 600)

Figure 2

FNA smear from left axillary lymph node showing megakaryocyte (giant cell with multilobated nucleus without hyperchromasia or prominent nucleolus) (MGG, × 600)

In corroboration with the PBF findings, a diagnosis of partial infiltration by lymphoblastic leukemia and evidence of EMH with megakaryocytes in the left axillary lymph node was made. The cervical lymph node was diagnosed as reactive lymphoid hyperplasia. A complete hemogram with a bone marrow examination was advised.

The hemogram showed hemoglobin of 7.6 g/dL; total leucocyte count of 8900/μL; differential leucocyte count (DLC) neutrophils-17%, lymphocytes-64%, monocytes-02%, blasts 12%; platelet count -14,000/μL and nRBCs 2/100 white blood cells. Bone marrow smears were hypercellular and showed 96% blasts, which were small sized with high nucleus to cytoplasmic (N:C) ratio and 0–1 small nucleoli. Cytochemistry was performed and the blasts were negative for myeloperoxidase, Sudan Black B and Periodic acid Schiff stain. Total Binets score was two plus and a diagnosis of acute lymphoblastic leukemia (ALL)-L1 was given. The erythroid, myeloid and megakaryocytic series were markedly depressed. Bone marrow trephine biopsy showed diffuse replacement of marrow spaces by the lymphoblasts, with marked paucity of myeloid, megakaryocytic and erythroid precursors.

Discussion

Generalised or localized lymphadenopathy preceding or developing in association with leukemia is known, yet not very common.

In the current case, the patient was referred to cytology clinic for FNA and initial diagnostic work-up. Clinically, both an infectious etiology and neoplastic pathology were suspected. The axillary lymph node was tender and larger than the other nodes. In the interpretation of the axillary lymph node aspirate smears, two main difficulties were encountered, (1) Recognition of the lymphoblasts as leukemia cells (neoplastic process): Since lymphoblasts are present in a reactive lymph node, it was difficult to distinguish whether the lymphoblasts were part of the florid reactive process of the lymph node or infiltration by the leukaemic blasts. A major part of the smear showed monomorphic population of lymphoblasts with hand mirror cells, teat cells with lymphoglandular bodies in the background, with very few interspersed mature lymphocytes. Lymphohistiocytic clusters and follicle centre cells (centroblasts and centrocytes) were absent. These features favored the diagnosis of lymphoma–leukemia rather than a reactive process, analogous to a non-Hodgkin's lymphoma. However, with the presence of pancytopenia and lymphoid blasts in the peripheral smear, first possibility kept was of acute leukemia. This was confirmed on the bone marrow, which revealed acute leukemia. (2) Recognition of the giant cells as megakaryocytes: Anumber of differential diagnoses were kept for large cells with polylobated nuclei in lymph node aspirate smears, which included variant of Reed–Sternberg (RS) cells, syncytial giant cells due to viral infection, megakaryocytes and metastatic carcinoma cells. In our case, the cells had uniform chromatin with absence of large prominent nucleoli, which was an important distinguishing feature to exclude RS cells and metastatic malignant cells.

Cells of other hematopoietic series, i.e. metamyelocytes and nucleated RBCs, were also present in the smears. Thus, the large cells were recognized to be megakaryocytes, as a part of extramedullary hematopoietic process. Subsequent bone marrow findings of infiltration by leukaemic blasts with marked paucity of the myeloid and megakaryocytic series support the diagnosis.

Diagnosis of leukemic lymphadenopathy is necessary for planning treatment. FNA diagnosis is straightforward in patients with prior diagnosis of leukemia. In suspected cases of lymphoproliferative disorders, during FNA of the lymph nodes, it is advisable to make a peripheral smear along with FNA to rule out leukemic infiltration as was done in the present case. It is necessary because often FNA is the first investigation and no information is usually available on hematological status.

Without the relevant hematological investigations, differential diagnosis on FNAC smears is that of non-Hodgkin's lymphoma (NHL) and metastatic carcinoma. In a study by Kumar et al.,[1] FNA smears from lymph nodes of 14 cases of ALL were diagnosed as NHL during the initial screening. In four cases of ALL-L1, smears showed a monomorphic population of large lymphocytes (two to three times larger than RBCs) with inconspicuous cytoplasm. The nucleus occupied the entire cell and showed smooth chromatin. These cases were diagnosed as NHL, large cell, noncleaved type. On histopathological examination also, a diagnosis of NHL was given. However, after considering the clinical history and marrow diagnosis, all of them were rediagnosed as leukemic infiltration. The precise nature of the cells was identified more accurately with Wright-Giemsa stain and the cell morphology was better preserved in FNA smears than in biopsy material. Thus, clinical and hematological findings are essential for the differentiation of leukaemic smears from lymphoma.

Chen et al.[3] studied the diagnostic accuracy of FNAC in assessing extramedullary leukemic infiltration. Out of the 65 cases studied, there were 24 cases of ALL, 25 cases of acute myelogenous leukemia (AML), 6 cases of chronic lymphocytic leukemia (CLL) and 10 cases of chronic granulocytic leukemia (CML). The commonest site of infiltration was lymph node, which accounted for 73.8% of all cases. Morphological assessment under oil immersion lens and examination of peripheral blood smears was useful to distinguish leukemic infiltration from NHL.

In cases of CML, rarely, the first manifestation of blast crisis is at an extramedullary site, such as the lymph node, and it is difficult to differentiate CML from malignant lymphoma on routine lymph node biopsy.[2] Under such circumstances, FNA of the lymph node may help in rapid diagnosis because of the good morphological detail of blasts and other granulocytic cells on MGG stain.

EMH occurs when normal bone marrow function is insufficient or destroyed. It often involves the spleen, liver, lymph nodes and less frequently other organs such as the kidney, retroperitoneum, lungs, etc.[2] On FNA, Romanowsky stains are especially helpful in recognition of different hematopoietic cells such as granulocytic precursors, eosinophils, and megakaryocytes. Many theories concerning the pathogenesis of these lesions have been proposed, including the extrusion of bone marrow cells consequent to marrow fibrosis/replacement by other cells.[4] Others suggest reactivation of hematopoiesis in organs where it occurred in embryonic and fetal life, and increased number of circulating hematopoietic stem cells which embolise to different organs.[4]

Megakaryocytes can resemble multinucleated RS cells as RS cells can have a large, bilobed or multilobated nucleus with abundant, pale and fragile cytoplasm. However, the smears in Hodgkin's disease reveal a background of lymphocytes, plasma cells, histiocytes and eosinophils and the RS cells have huge prominent nucleoli.[5] A diagnosis of metastatic tumors can be ruled out by the recognition of distinct cytological features of megakaryocytes without hyperchromasia and prominence of nucleoli. Factor VIII immunoperoxidase stain can also be used to confirm the megakaryocytic lineage of the multinucleated cells.

To conclude, this was a unique case of a lymph nodal mass, diagnosed on FNAC as infiltration by leukemia along with features of EMH. Recognition of the different cells was possible with MGG staining. Clinical and PBF findings were crucial for the diagnosis.