Hashimoto's thyroiditis manifesting monoclonal lymphocytic infiltration

Observations on hematogones with light chain restriction

Light-chain restricted hematogones (LCR HGs) detected by flow cytometry (FC) may, occur in bone marrow mimicking involvement by a B-cell lymphoma. This phenomenon can present a diagnostic pitfall and negatively impact patient management, and may occur in other organs, including lymph nodes, For this reason, it is recommended to utilize, in case of LCR in lymph node, one additional morphological, phenotypical or molecular criteria for the diagnosis of lymphoma on cytological samples.

Hematogones with light chain restriction: A potential diagnostic pitfall when using flow cytometry analysis to assess bone marrow specimens

Light-chain restricted hematogones (LCR HGs) detected by flow cytometry analysis can mimic bone marrow involvement by B-cell lymphoma. This phenomenon can present a diagnostic pitfall and negatively impact patient management, as misinterpretation may upgrade disease stage. In this study, we characterized the immunophenotype of LCR HGs with an aim to differentiate them from B-cell lymphoma. We analyzed 24 patients with LCR HGs, 12 (50 %) were kappa light chain restricted and 12 (50 %) were lambda light chain restricted. LCR HGs account for 51 % (range, 1.5%-99%) of B cells, and 0.5 % (range, 0.1%-3.7%) of total cells. In 15 patients in whom multiple specimens were analyzed, 10 (67 %) showed persistent LCR HGs in more than 1 specimen, and the duration of the light chain restriction ranged from 4 months to 2 years. Among 24 patients, 4 (16.6 %) cases were concurrently involved by B-cell lymphoma/myeloma in addition to LCR HGs. With the exception of light chain restriction, LCR HGs showed a similar immunophenotype as normal HGs and had a distinct location on the CD45/Side Scatter (SSC) plot. They were also consistently positive for CD10, CD19, CD38 (bright), CD43, and CD200. CD20 expression showed a spectrum from dim/negative to positive.

Extranodal Lymphoproliferative Processes and Flow Cytometry

OBJECTIVE

Fine-needle aspiration (FNA) cytology is a safe and cost-effective technique for the diagnosis of lymphoproliferative processes, especially when correlated with clinical and imaging studies. However, cytology alone may be unable to detect a lymphoid neoplastic process, as architectural features are less obvious than in histologic preparations and, in certain cases, reactive processes may mimic lymphoma. Flow cytometry (FC) has been recognized as an important ancillary technique in the diagnosis of lymphoid neoplasms and it can be used in conjunction with FNA in the evaluation of lymphoproliferative processes.

STUDY DESIGN

We performed a review of the published literature concerning FC applied to the detection of salivary glands and thyroid lymphoproliferative processes, which are frequently related to autoimmune diseases and difficult to diagnose by cytomorphology alone.

RESULTS

FC is able to detect and subtype non-Hodgkin lymphomas and may contribute to the exclusion of a neoplastic process in cytologically unclear cases.

CONCLUSIONS

FC can be successfully applied in the differential diagnosis of lymphoproliferative processes in the head and neck region. The FNA-FC combined approach can reduce time to therapy and may prevent unnecessary surgical biopsies.

Myasthenia Gravis: paradox versus paradigm in autoimmunity

Myasthenia Gravis (MG) is a paradigm of organ-specific autoimmune disease (AID). It is mediated by antibodies that target the neuromuscular junction. The purpose of this review is to place MG in the general context of autoimmunity, to summarize the common mechanisms between MG and other AIDs, and to describe the specific mechanisms of MG. We have chosen the most common organ-specific AIDs to compare with MG: type 1 diabetes mellitus (T1DM), autoimmune thyroid diseases (AITD), multiple sclerosis (MS), some systemic AIDs (systemic lupus erythematous (SLE), rheumatoid arthritis (RA), Sjogren's syndrome (SS)), as well as inflammatory diseases of the gut and liver (celiac disease (CeD), Crohn's disease (CD), and primary biliary cirrhosis (PBC)). Several features are similar between all AIDs, suggesting that common pathogenic mechanisms lead to their development. In this review, we address the predisposing factors (genetic, epigenetic, hormones, vitamin D, microbiota), the triggering components (infections, drugs) and their interactions with the immune system [1,2]. The dysregulation of the immune system is detailed and includes the role of B cells, Treg cells, Th17 and cytokines. We particularly focused on the role of TNF-α and interferon type I whose role in MG is very analogous to that in several other AIDS. The implication of AIRE, a key factor in central tolerance is also discussed. Finally, if MG is a prototype of AIDS, it has a clear specificity compared to the other AIDS, by the fact that the target organ, the muscle, is not the site of immune infiltration and B cell expansion, but exclusively that of antibody-mediated pathogenic mechanisms. By contrast, the thymus in the early onset subtype frequently undergoes tissue remodeling, resulting in the development of ectopic germinal centers surrounded by high endothelial venules (HEV), as observed in the target organs of many other AIDs.

CD8+ T-Cell Deficiency, Epstein-Barr Virus Infection, Vitamin D Deficiency, and Steps to Autoimmunity: A Unifying Hypothesis

CD8+ T-cell deficiency is a feature of many chronic autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's syndrome, systemic sclerosis, dermatomyositis, primary biliary cirrhosis, primary sclerosing cholangitis, ulcerative colitis, Crohn's disease, psoriasis, vitiligo, bullous pemphigoid, alopecia areata, idiopathic dilated cardiomyopathy, type 1 diabetes mellitus, Graves' disease, Hashimoto's thyroiditis, myasthenia gravis, IgA nephropathy, membranous nephropathy, and pernicious anaemia. It also occurs in healthy blood relatives of patients with autoimmune diseases, suggesting it is genetically determined. Here it is proposed that this CD8+ T-cell deficiency underlies the development of chronic autoimmune diseases by impairing CD8+ T-cell control of Epstein-Barr virus (EBV) infection, with the result that EBV-infected autoreactive B cells accumulate in the target organ where they produce pathogenic autoantibodies and provide costimulatory survival signals to autoreactive T cells which would otherwise die in the target organ by activation-induced apoptosis. Autoimmunity is postulated to evolve in the following steps: (1) CD8+ T-cell deficiency, (2) primary EBV infection, (3) decreased CD8+ T-cell control of EBV, (4) increased EBV load and increased anti-EBV antibodies, (5) EBV infection in the target organ, (6) clonal expansion of EBV-infected autoreactive B cells in the target organ, (7) infiltration of autoreactive T cells into the target organ, and (8) development of ectopic lymphoid follicles in the target organ. It is also proposed that deprivation of sunlight and vitamin D at higher latitudes facilitates the development of autoimmune diseases by aggravating the CD8+ T-cell deficiency and thereby further impairing control of EBV. The hypothesis makes predictions which can be tested, including the prevention and successful treatment of chronic autoimmune diseases by controlling EBV infection.

High response rate and improvement of long-term survival with combined treatment modalities in patients with poor-risk primary thyroid diffuse large B-cell lymphoma: an International Extranodal Lymphoma Study Group and Intergruppo Italiano Linfomi study

The impact of different treatment modalities and prognostic factors on the clinical course of primary thyroid diffuse large B-cell lymphoma (PTDLBCL) is still the subject of research. This study was conducted to clarify these clinical aspects of this disorder. The clinical parameters of 48 patients with PTDLBCL at time of diagnosis were comparable to those of previous studies. Patients underwent either radiotherapy (RT)  ±  surgery (SX), chemotherapy (CHT) alone or in combination with local treatments (RT or SX), or SX followed by CHT and RT. A 90% complete remission (CR) rate was observed among patients who underwent combined treatment modalities (CTM), compared to 76% among the others. The 5-year progression-free survival differed significantly between both groups (p = 0.028). Poor performance status and advanced age correlated with decreased survival. PTDLBCL is a curable disease prevalent in elderly patients. Combined treatment modalities were able to induce an elevated rate of CR, improving long-term survival in younger patients. However, the outcome in elderly patients still remains unsatisfactory.

Nodal and extranodal plasmacytomas expressing immunoglobulin a: an indolent lymphoproliferative disorder with a low risk of clinical progression

Plasmacytomas expressing immunoglobulin A are rare and not well characterized. In this study, 9 cases of IgA-positive plasmacytoma presenting in lymph node and 3 in extranodal sites were analyzed by morphology, immunohistochemistry, and polymerase chain reaction examination of immunoglobulin heavy and κ light chain genes. Laboratory features were correlated with clinical findings. There were 7 males and 5 females; age range was 10 to 66 years (median, 32 y). Six of the patients were younger than 30 years of age, 5 of whom had nodal disease. About 67% (6 of 9) of the patients with nodal disease had evidence of immune system dysfunction, including human immunodeficiency virus infection, T-cell deficiency, autoantibodies, arthritis, Sjögren syndrome, and decreased B cells. An IgA M-spike was detected in 6 of 11 cases, and the M-protein was nearly always less than 30 g/L. All patients had an indolent clinical course without progression to plasma cell myeloma. Histologically, nodal IgA plasmacytomas showed an interfollicular or diffuse pattern of plasma cell infiltration. The plasma cells were generally of mature Marschalko type with little or mild pleomorphism and exclusive expression of monotypic IgA. There was an equal expression of κ and λ light chains (ratio 6:6). Clonality was showed in 9 of 12 cases: by polymerase chain reaction in 7 cases, by cytogenetic analysis in 1 case, and by immunofixation in 1 case. Clonality did not correlate with pattern of lymph node infiltration. Our results suggest that IgA plasmacytomas may represent a distinct form of extramedullary plasmacytoma characterized by younger age at presentation, frequent lymph node involvement, and low risk of progression to plasma cell myeloma.

Clonal B-cell population in a reactive lymph node in acquired immunodeficiency syndrome

A 40-year-old female, HIV positive, stage C, since 4 years, complained of a right cervical lymph node swelling. Two years before, the patient had been diagnosed with follicular B-cell non-Hodgkin lymphoma (FL); she had been treated with four cycles of multiagent chemotherapy plus rituximab, the last cycle being administered 10 months before coming to our attention. An ultrasound (US) guided fine-needle cytology (FNC) showed an atypical lymphoid cell proliferation. The phenotype evidenced by flow cytometry (FC) analysis was D5: 10%, CD19: 49%, CD23: 10%, FMC7: 0%, CD10: 40%, CD10/19: 40%, lambda light chain 40%, kappa light chain 0%. FDG-positron emission tomography (PET/CT) scan showed positivity in the corresponding cervical area. Since low LDH values and a reduced lymph node size were observed, the lymph node was therefore excised; the histology revealed a reactive hyperplastic lymph node with florid follicular pattern. A subsequent PCR analysis, performed on DNA extracted from a whole histological section, did not evidence IgH rearrangement. The patient is currently undergoing strict clinical and instrumental follow-up, including PET every 3 months; after 13 months, she is alive without recurrence of lymphoma. Clonal B-cell populations in non-lymphomatous processes have been described in mucosa-associated lymphoid cell populations and reactive lymph nodes, and are considered non-malignant, antigen driven, proliferations of B-lymphocytes determined by an abnormal response to bacterial or viral antigen stimulation. The present case occurred in an HIV patient and was clinically complex because of the patient's history of FL. This experience suggests much attention in the evaluation of radiological, cytological, and FC data and in clinical correlation in patients suffering from autoimmune or immunodeficiency syndromes.

Cytologic, flow cytometry, and molecular assessment of lymphoid infiltrate in fine-needle cytology samples of Hashimoto thyroiditis

BACKGROUND

The thyroidal lymphoid infiltrate (TLI) in Hashimoto thyroiditis (HT) represents the substrate from which thyroid lymphoma may arise. The objective of the current study was to classify the TLI in HT by comparing the cytologic features with flow cytometry (FC) data and evaluating the kappa/lambda light chain ratio and its molecular assessment.

METHODS

Fine-needle aspiration cytology (FNAC) was performed in 34 patients with HT with nodular or diffuse palpable enlargement of the gland. Two or 3 passes were performed to prepare traditional smears, FC, and immunophenotyping, and RNAlater suspensions for molecular assessment. FC was performed using the following antibodies: CD3, CD5, CD4, CD8, CD10, CD19, and kappa and lambda light chains. In 4 cases, high molecular weight DNA was extracted and used for polymerase chain reaction (PCR) to amplify the variable diversity joining region of the heavy chain immunoglobulin (Ig) genes (IgH). Statistical analysis was performed to evaluate possible associations between clinical ultrasound presentation, cytologic pattern, and TLI phenotype. Light chain expression was evaluated as the percentage of the expressing cells (</=20% and >20%) and as the kappa/lambda ratio.

RESULTS

Smears were classified as "lymphocytic," "lymph node-like," or "mixed." FC demonstrated T cells (CD3 positive [+], CD5+) in all cases, and T cells and B cell (CD19+, CD10+/-) lymphocytes in 22 cases. Light chains were expressed in 30 cases (in <20% of the gated cells in 13 cases and in >20% of the gated cells in 17 cases). Five cases demonstrated small kappa/lambda ratio imbalances and PCR analysis demonstrated diffuse bands in the gel and Gaussian curves at the heteroduplex. Statistical analysis indicated significant associations between the "lymphocytic" pattern and T-cell phenotype and between the "lymph node-like" pattern and B-cell phenotype. A significant association also was observed between light chain restriction and low light chain expression (P < .005).

CONCLUSIONS

The cytologic pattern of TLI in HT is quite representative of the clinical presentation and phenotypic cell type. Small light chain imbalances are not sustained by heavy chain Ig gene (IgH) rearrangements. FNA coupled with FC may contribute to making the distinction between florid TLI and non-Hodgkin lymphoma.

Pitfalls of diagnosis based on abnormal flow cytometry and [(18)F]fluorodeoxyglucose positron emission tomography

A 30-year-old, HIV-positive man with a previous history of an atypical nasopharyngeal Burkitt lymphoma developed fluorodeoxyglucose (FDG) avidity on a routine FDG-positron emission tomography (PET)/computed tomography scan performed 10 months after the completion of all treatment. This new FDG-avid disease was in the area of his initial disease. Flow cytometric assessment of a fine needle aspiration showed a CD10-expressing B-cell population with kappa predominance. The corresponding cytology smears had large atypical lymphoid cells along with smaller lymphocytes and macrophages. Because of the patient's previous history of a CD10(+), high-grade B-cell lymphoma, the cytologic and flow cytometric findings were considered highly suspicious for a B-cell lymphoma. Because the differential diagnosis included a relapsed Burkitt lymphoma versus a second, unrelated lymphoma (the former with a dismal prognosis) it was deemed prudent to obtain more tissue via an open biopsy for confirmation of diagnosis and exact subclassification. An open biopsy, however, revealed a reactive lymph node with enlarged geographic follicles; no lymphoma was demonstrable and c-Myc studies were negative. The patient remains without evidence of disease. Retrospectively, the original flow cytometric assessment was believed to likely represent sampling of hyperplastic germinal centers with significantly expanded CD10(+) B cells. The FDG uptake and the kappa predominance further confounded the interpretation. This case illustrates the pitfalls of standard diagnostic techniques, including PET scanning, cytology, and flow cytometry, particularly in the setting of HIV. It further underscores the importance of adequate clinical correlation and a low threshold for performing open biopsies in such patients.

Clonal relationship between Hashimoto thyroiditis and thyroid lymphoma

BACKGROUND

Although Hashimoto thyroiditis (HT) is a predisposing factor for B-lineage thyroid lymphoma, clonal B-cell populations in HT are rare.

AIM

To investigate whether there is a clonal relationship between HT and primary thyroid lymphoma.

METHODS

Clonalilty and sequence similarity was determined by PCR followed by sequencing and comparing immunoglobulin heavy chain (IgH) gene rearrangement sequences to germline sequences and to each other.

RESULTS

12/20 patients with primary thyroid lymphoma had a previous history and histological diagnosis of HT. Clonal IgH bands associated with a polyclonal background were present in four of these 12 cases of HT; of these four, three had reproducible clonal IgH bands from the subsequently developed lymphoma. The range of similarity (homology) of multiple clonal bands in HT with the germline IgH varied from 90% to 96.3%. Multiple clonal bands in HT had sequence similarity (homology) of 62-100% with the clonal band in the lymphoma from the same patient. At least one clonal band in HT had more than 96% similarity (homology) with the clonal band of lymphoma in all three cases.

CONCLUSION

Sequence similarity between the clonal bands in HT and subsequently developed thyroid lymphoma is supportive of the argument that primary thyroid lymphoma may evolve from HT.

Isolation of thyroid cells obtained by fine-needle aspiration biopsy

Usually thyroid cells isolated from tissue obtained by surgery or thyroid cell lines are used to investigate the pathogenesis of autoimmune thyroid diseases. Isolation and cultivation of thyrocytes from fine-needle aspiration biopsy (FNAB) has not yet been published. The aim of this study was to isolate and cultivate thyrocytes from samples of FNAB. FNAB samples were obtained from nine adults and nine children with Hashimoto's thyroiditis (HT). The aspiration material was filtered resulting in small samples of tissue on the surface of the filter membrane. These tissue fragments were digested by collagenase I and dispase II. The yielding cells were cultivated for 3 weeks in Ham's F12 Kaighn's Modification medium in presence of 1 mU/mL bovine thyrotropin (TSH), 10 microg/mL human insulin, 6 microg/mL transferrin, and 10(-8) M hydrocortisone. Finally, isolated thyroid cells were characterized by determination of gene expression of thyrotropin receptor (TSHR), thyroperoxidase (TPO), and thyroglobulin (Tg) using a nested reverse transcriptase-polymerase chain reaction (RT-PCR). Thyroid cells obtained by FNAB can be maintained over a time period of approximately 3 weeks. Depending on the sample size a final number of 1000-14,000 cells was gained per FNAB. In addition, all cells isolated by the described method expressed TPO mRNA. TSHR mRNA was found in 4 samples, whereas 15 samples were Tg mRNA-positive. There were no differences with respect to the expression TSHR and TPO mRNA between samples from adults and children. The isolation and cultivation of thyroid cells obtained by FNAB has been established. In contrast to surgical specimen, this technique provides an easy access to thyrocytes derived from individual patients allowing repeated sampling to investigate the time progression of the chronic disease or the effect of treatment over time.

Clonal B cell populations in a minority of patients with Hashimoto's thyroiditis

BACKGROUND

Hashimoto's thyroiditis (HT) is a risk factor for thyroid lymphoma, and clonal B cell populations in HT support this link. The literature on B cell clonality in HT is controversial.

AIMS

To identify clonal B cell populations in HT and to assess their usefulness in differentiating HT from mucosa associated lymphoid tissue (MALT) lymphoma and predicting future development of lymphoma.

METHODS

DNA from formalin fixed, paraffin wax embedded blocks of thyroid specimens from 10 patients with HT and two thyroid MALT lymphomas was analysed for B cell clonality by seminested polymerase chain reaction (PCR) using FRIII/LJH and FRIII/VLJH primers to amplify the IgH gene VDJ region. In one case, PCR products were sequenced. Immunohistochemistry was performed by labelled streptavidin-biotin technique using antibodies to: CD45, CD45RO, CD3, CD20, and cytokeratin.

RESULTS

The histopathological and clinical findings were characteristic of HT. Clonal bands were seen in three and a polyclonal smear pattern was seen in seven cases. The clonal bands in HT were associated with a background smear, and could not be reproduced from other blocks from the same case or from deeper sections of the same block. The clonal bands in thyroid lymphomas were not associated with a background smear and were reproducible. None of the patients with clonal B cells has developed malignant lymphoma during a follow up of 10-13 years.

CONCLUSIONS

B cell clonal bands in HT have different features from those in lymphoma (non-pure and non-reproducible) and do not predict future development of lymphoma.

Infection of autoreactive B lymphocytes with EBV, causing chronic autoimmune diseases

I hypothesize that human chronic autoimmune diseases are based on infection of autoreactive B lymphocytes by Epstein-Barr virus (EBV), in the following proposed scenario. During primary infection, autoreactive B cells are infected by EBV, proliferate and become latently infected memory B cells, which are resistant to the apoptosis that occurs during normal B-cell homeostasis because they express virus-encoded anti-apoptotic molecules. Genetic susceptibility to the effects of B-cell infection by EBV leads to an increased number of latently infected autoreactive memory B cells, which lodge in organs where their target antigen is expressed, and act there as antigen-presenting cells. When CD4(+) T cells that recognize antigens within the target organ are activated in lymphoid organs by cross-reactivity with infectious agents, they migrate to the target organ but fail to undergo activation-induced apoptosis because they receive a co-stimulatory survival signal from the infected B cells. The autoreactive T cells proliferate and produce cytokines, which recruit other inflammatory cells, with resultant target organ damage and chronic autoimmune disease.

Molecular genetics of extranodal marginal zone (MALT-type) B-cell lymphoma

Mucosa-associated lymphoid tissue lymphoma is now classified as extranodal marginal zone B-cell lymphoma. We reviewed the current literature on the biological and genetic mechanisms that lead to the development and progression of this unusual lymphoma. Particular attention was given to the clinical and biological significance of the immunoglobulin genes rearrangement, that has been proposed and widely used both diagnostically and as a tool to monitor the response to antibiotic treatment.

Computer-assisted image analysis of small cell lymphoma of the thyroid gland. Comparison of nuclear parameters of small lymphocytes in lymphomas and Hashimoto's thyroiditis

The nuclear parameters of the small lymphocytes in nine cases of small cell lymphomas of the thyroid gland and 17 cases of Hashimoto's thyroiditis were assessed by computer-assisted image analysis. The nuclear area, maximal, minimal and averaged Ferret diameters, perimeter, regularity factor and elongation factor were gauged. Statistically, the nuclear area was ascertained to be the optimum descriptor discriminating between small neoplastic and reactive lymphocytes. Application of a novel variable, combining a nuclear area cut-off value of 14 microm2 with a nuclear averaged Ferret diameter cut-off value of 4.5 micron, allows for the distinction - with a high degree of sensitivity and specificity - between small neoplastic lymphocytes in thyroidal lymphomas and the reactive lymphocytes in Hashimoto's thyroiditis.

Usefulness of surface phenotype study of intrathyroidal lymphocytes obtained by fine needle aspiration cytology in autoimmune thyroid disease and malignant lymphoma of the thyroid

OBJECTIVES

The surface phenotypes of intrathyroidal lymphocytes have been studied in various thyroid diseases. In most of the previous reports, intrathyroidal lymphocytes were obtained by surgical operation. We evaluated the usefulness of surface phenotype study of intrathyroidal lymphocytes obtained by fine needle aspiration in the diagnosis of Graves' disease, chronic thyroiditis, and malignant lymphoma of the thyroid.

PATIENTS AND DESIGN

Eighty-seven untreated patients including 24 with Graves' disease, 59 with chronic thyroiditis, and 4 with malignant lymphoma of the thyroid, and 2 treated patients with malignant lymphoma of the thyroid were studied. Surface phenotypes of the peripheral lymphocytes and the intrathyroidal lymphocytes obtained by fine needle aspiration were analyzed using a FACScan and the monoclonal antibodies: anti-Leu5b/CD2, Leu4/CD3, Leu3a/CD4, Leu2a/CD8, and Leu12/CD19. Percentages of cells positive for each monoclonal antibody were calculated. In one case with malignant lymphoma, monoclonal antibodies to surface-immunoglobulin markers were also studied.

RESULTS

In peripheral lymphocytes, the percentage of positive cells in each phenotype was almost normal in each disease. In intrathyroidal lymphocytes, the percentage of CD19 positive cells was increased, and the percentage of CD2 and CD3 positive cells was reduced compared to those of peripheral lymphocytes in each disease. The percentage of intrathyroidal CD19 positive cells was remarkably high in malignant lymphoma, constituting more than 70% of cells. In Graves' disease, a relative decrease in the percentage of intrathyroidal CD4 positive cells and an increase in CD8 positive cells compared to peripheral lymphocytes were observed. In 2 treated patients with malignant lymphoma of the thyroid, the intrathyroidal CD19 positive cells almost disappeared in a patient shortly after successful treatment, and reappeared to constitute 76% of cells in a patient in relapse. In one case with malignant lymphoma in which monoclonal antibodies to surface-immunoglobulin markers were studied, the clonality of the affected cells could be demonstrated; more than 70% of the cells were positive for kappa light-chain and mu and delta heavy-chain. This finding was proved by subsequent immunohistochemical study based on open biopsy.

CONCLUSIONS

Surface phenotype study of intrathyroid lymphocytes obtained by fine needle aspiration has limited utility in the evaluation or diagnosis of Graves' disease and chronic thyroiditis. However, this simple rapid method is very helpful in the diagnosis and follow up of malignant lymphoma of the thyroid.

Flow cytometry in diagnostic cytology

Flow cytometry (FCM) is a useful adjunct to cytologic examination, because the quantitative biochemical information it provides complements the morphologic information gained during visual examination. It aids in the interpretation of bladder washings, and is particularly useful for the assessment of lymphoid lesions, whether they originate from fine-needle aspiration, cerebrospinal fluid, or effusions. Optimal use of FCM frequently requires assessment of more than one parameter; simultaneous use of cell differentiation markers and nuclear DNA quantitation is often significantly more useful than either alone. Despite the utility of FCM, however, the potential for future development appears to be limited. Improvements in image cytometry allow reasonable assessment of ploidy and S-fraction to be made from specimens prepared on glass slides. Multiparameter measurements may also be accomplished with imaging techniques, which allow the further advantage of visual identification of cells with equivocal morphologic changes. The development of artificial intelligence methods for use with imaging technology has also significantly exceeded that of FCM. Finally, image cytometry is often more useful for samples with few cells. Other challenges are posed by immunocytochemical methods which compete with flow cytometry as tools for assessment of proliferation. Given the relatively high cost of FCM instrumentation, survival of FCM as an ancillary technique in cytopathology will require further technical refinements to offset the advantages currently associated with image cytometry and immunocytochemistry.