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Year : 2020  |  Volume : 63  |  Issue : 1  |  Page : 131-133
Leptomeningeal involvement by relapsed follicular lymphoma detected by flow cytometry despite exceedingly low white blood cell counts in cerebrospinal fluid: A case report

Department of Pathology and Laboratory Medicine, Hartford Hospital, Hartford, Connecticut, USA

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Date of Web Publication31-Jan-2020


Follicular lymphoma is usually an indolent non-Hodgkin lymphoma that rarely involves the central nervous system (CNS) and flow cytometric detection of such lymphoma in cerebrospinal fluid (CSF) is often challenging because of low cellularity and viability of CSF samples. Here, we report our experience in a 52-year-old man whose relapsed follicular lymphoma with leptomeningeal involvement was confirmed by flow cytometric analysis of CSF, despite an exceedingly low white blood cell count (3/cumm).

Keywords: Cerebrospinal fluid, flow cytometry, follicular lymphoma, leptomeningeal involvement, low cellularity

How to cite this article:
Hafeez S, Cho WC, Shen P. Leptomeningeal involvement by relapsed follicular lymphoma detected by flow cytometry despite exceedingly low white blood cell counts in cerebrospinal fluid: A case report. Indian J Pathol Microbiol 2020;63:131-3

How to cite this URL:
Hafeez S, Cho WC, Shen P. Leptomeningeal involvement by relapsed follicular lymphoma detected by flow cytometry despite exceedingly low white blood cell counts in cerebrospinal fluid: A case report. Indian J Pathol Microbiol [serial online] 2020 [cited 2022 Oct 5];63:131-3. Available from:

   Introduction Top

Follicular lymphoma (FL) is the most common type of non-Hodgkin lymphoma (NHL) of germinal/follicular center B cell origin. Generally indolent, FL predominantly affects adults in the sixth decade of life and typically presents as generalized lymphadenopathy. It may also involve other extranodal sites, such as the spleen, bone marrow, peripheral blood, and less commonly Waldeyer ring. Involvement of the central nervous system (CNS) by such indolent NHL, however, is still rare and usually occurs following histologic transformation to a higher grade, more aggressive form of lymphoma. In patients with suspected CNS involvement by primary or secondary lymphomas, flow cytometric analysis (FCA) of cerebrospinal fluid (CSF) is frequently utilized to detect an aberrant clonal population, in conjunction with conventional cytomorphologic examination. However, the low cellularity and rapidly declining viability of white blood cells (WBCs) in CSF samples often pose a diagnostic challenge for pathologists. Herein, we describe a case of relapsed FL involving the CNS in a 52-year-old man whose leptomeningeal involvement was confirmed by concurrent cytologic examination and FCA, despite an exceedingly low WBC count of 3/cumm in CSF.

   Case Report Top

A 52-year-old man, who had been in remission for 10 years following the initial diagnosis of FL and subsequent therapy with rituximab, presented with diffuse lymphadenopathies. Excisional left groin lymph node biopsy showed an effaced architecture composed of intermediate size lymphocytes with angulated nuclei, variably prominent nucleoli, and moderate cytoplasm arranged predominantly in nodules with expanded interfollicular areas. Mitotic activity was increased. FCA identified a CD10-positive, lambda-restricted, B-cell population. By immunohistochemistry, the neoplastic cells were CD20-positive with coexpression of BCL2 and CD10, and were located both in CD21-positive follicles and in the interfollicular distribution. Ki-67 revealed an elevated proliferation index of approximately 40%. The findings were most consistent with involvement by FL, World Health Organization grade 2-3A with a follicular growth pattern. Following the fifth cycle of chemotherapy with bendamustine and rituximab, however, the patient was found to have diplopia and left ptosis consistent with left third nerve palsy, raising the possibility of leptomeningeal involvement by relapsed FL. CSF obtained was grossly clear and colorless, measuring approximately 1 mL in volume. FCA of CSF, with a WBC count of 3/cumm, showed an abnormal B-cell population comprising 60% of total cells with slightly increased forward and side scatters. The abnormal B-cells displayed CD10, CD19 (dim partial), CD45, and lambda restriction [Figure 1]a in the absence of definitive CD20 or CD5 expression. T-cells were found to have both CD4-positive and CD8-positive subsets with a CD4:CD8 ratio of 1:1. Cytology revealed rare abnormal cells with scant cytoplasm and cleaved nuclei [Figure 1]b. FCA of peripheral blood also showed the same abnormal B-cell population as seen in CSF. The findings were most consistent with CNS involvement relapsed FL. Subsequent bone marrow aspirate and biopsy were unremarkable with normocellular marrow with trilineage hematopoiesis with no evidence of involvement by FL, however.
Figure 1: Flow cytometric analysis of cerebrospinal fluid (1 mL, white blood cell count of 3 cells per microliter) and cytologic examination. (a) By polychromatic flow cytometry, an abnormal B-cell population (approximately 60% of total cells) with slightly increased forward and side scatters was identified. These cells displayed CD10, CD19 (dim partial), CD45 (not shown), and lambda-restriction. (b) On cytologic examination, atypical lymphoid cells with cleaved or indented nuclei and scant cytoplasm were noted. 254 × 190 mm (96 × 96 DPI)

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Formal written informed consent was not required with a waiver by the appropriate institutional review board of Hartford Hospital and/or national research ethics committee.

   Discussion Top

Involvement of the CNS by lymphomas, regardless of whether it is primary or secondary, is an uncommon but nearly always fatal complication.[1] Primary CNS lymphomas account for approximately 3% of all primary CNS neoplasms and may involve the brain parenchyma, leptomeninges, spinal cord, and ocular adnexa.[2],[3] Secondary or systemic involvement of the CNS is seen in approximately 5% of patients with NHLs and is generally secondary to involvement by high-grade, aggressive NHLs either forming intraparenchymal masses or, more frequently, infiltrating the leptomeninges.[4] Secondary involvement by indolent NHLs, such as FL, however, is uncommon occurring in only approximately 3% of patients with indolent NHLs.[1]

Cytomorphologic examination of CSF, which long has been regarded as the “gold standard” for diagnosing CNS lymphoma, has a relatively low sensitivity with a reported false-negative rate ranging from 20-60%.[1] Morphologic distinction between neoplastic cells and background reactive lymphocytes on cytospin preparation may not always be straightforward, especially in CSF samples with low cell counts. Consequently, flow cytometry, a highly sensitive and objective tool capable of, for example, reliably detecting an aberrant monoclonal B-cell population constituting as few as 0.01-0.9% of total lymphocytes,[5],[6],[7] has been the increasingly popular method of choice in patients with suspected CNS involvement by hematologic malignancies. Currently, in patients with high clinical suspicion for either primary or secondary CNS lymphomas, concurrent cytologic assessment and FCA of CSF are recommended by the National Comprehensive Cancer Network.[3] In fact, a recent study by Pittman et al.[8] further demonstrated the efficacy of FCA of CSF samples as a screening tool for diagnosing CNS lymphomas; in their study, a positive diagnosis was more likely in the presence of either a history of hematologic malignancy or a radiographic suspicion for lymphoma, and the positive and negative predictive values of combined cytomorphologic examination and FCA in such settings were 92% and 89%, respectively, when compared with tissue biopsy. However, the low volume and paucity of cells in CSF samples, coupled with the rapidly declining WBC viability following lumbar puncture, are limitations frequently encountered when examining CSF samples via flow cytometry.[9]

In the presented case, the WBC count of CSF was only 3 cells/cumm, which may be considered by many laboratories as “within normal range” (<5 leukocytes per microliter), particularly in the absence of a clinical suspicion for leptomeningeal localization of hematologic malignancies.[9] Despite the paucity of leukocytes and low volume (approximately 1 mL) in our CSF sample, however, an abnormal CD10-positive, lambda-restricted, B-cell population suggestive of involvement by relapsed FL was still successfully captured. Furthermore, cytologic examination also further supported our flow cytometric findings, revealing abnormal lymphocytes, albeit rare, with occasional cleaved nuclei and scant cytoplasm. The minimum volume and number of WBCs required for detection of an aberrant clonal population in CSF samples is not well established. Subira et al.[10] previously demonstrated that identification of CSF T lymphocytes, CD4-positive, and CD8-positive T cells could reliably be achieved in CSF samples with as few as 1 leukocyte/3 mL; however, detection of B lymphocytes required at least 5 cells/mL in their study.

In conclusion, we report a rare example of relapsed indolent NHL involving the CNS which was successfully detected by combination of cytologic examination and FCA of CSF despite an exceedingly low WBC count. To the best of our knowledge, this is the first reported case wherein leptomeningeal involvement by FL was captured via CSF flow cytometry with a WBC count of 3 cells/cumm, the lowest cell count in CSF ever reported to date. Our case also highlights the efficacy of FCA of CSF, when combined with a right clinical context and a positive cytologic finding, which may also be useful for screening for leptomeningeal involvement by indolent NHLs, such as FL.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Colocci N, Glantz M, Recht L. Prevention and treatment of central nervous system involvement by non-Hodgkin's lymphoma: A review of the literature. Semin Neurol 2004;24:395-404.  Back to cited text no. 1
Gerstner ER, Batchelor TT. Primary central nervous system lymphoma. Arch Neurol 2010;67:291-7.  Back to cited text no. 2
Brem SS, Bierman PJ, Brem H, Butowski N, Chamberlain MC, Chiocca EA, et al. National Comprehensive Cancer Network. Central nervous system cancers. J Natl Compr Canc Netw 2011;9:352-400.  Back to cited text no. 3
Bishop PC, Wilson WH, Pearson D, Janik J, Jaffe ES, Elwood PC. CNS involvement in primary mediastinal large B-cell lymphoma. J Clin Oncol 1999;17:2479-85.  Back to cited text no. 4
French CA, Dorfman DM, Shaheen G, Cibas ES. Diagnosing lymphoproliferative disorders involving the cerebrospinal fluid: Increased sensitivity using flow cytometric analysis. Diagn Cytopathol 2000;23:369-74.  Back to cited text no. 5
Bromberg JEC, Breems DA, Kraan J, Bikker G, van der Holt B, Smitt PS, et al. CSF flow cytometry greatly improves diagnostic accuracy in CNS hematologic malignancies. Neurology 2007;68:1674-9.  Back to cited text no. 6
Hegde U, Filie A, Little RF, Janik JE, Grant N, Steinberg SM, et al. High incidence of occult leptomeningeal disease detected by flow cytometry in newly diagnosed aggressive B-cell lymphomas at risk for central nervous system involvement: The role of flow cytometry versus cytology. Blood 2005;105:496-502.  Back to cited text no. 7
Pittman M, Treese S, Chen L, Frater JL, Nguyen TT, Hassan A, et al. Utility of flow cytometry of cerebrospinal fluid as a screening tool in the diagnosis of central nervous system lymphoma. Arch Pathol Lab Med 2013;137:1610-8.  Back to cited text no. 8
de Graaf MT, de Jongste AH, Kraan J, Boonstra JG, Sillevis Smitt PA, Gratama JW. Flow cytometric characterization of cerebrospinal fluid cells. Cytometry B Clin Cytom 2011;80:271-81.  Back to cited text no. 9
Subira D, Castanon S, Aceituno E, Hernández J, Jiménez-Garófano C, Jiménez A, et al. Flow cytometric analysis of cerebrospinal fluid samples and its usefulness in routine clinical practice. Am J Clin Pathol 2002;117:952-8.  Back to cited text no. 10

Correspondence Address:
Safina Hafeez
Department of Pathology and Laboratory Medicine, Hartford Hospital, 80 Seymour Street, Hartford, Connecticut 06102-5037
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_67_19

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