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December 2014 - Test your knowledge in the quiz!

What causes this mild lymphocytosis and thrombocytopenia? Healthy individual
Post-infectious lymphocytosis
Idiopathic thrombocytopenic purpura (ITP)
B-cell chronic lymphatic leukaemia (B-CLL)


Online version of this month`s case:

THE CORRECT ANSWER TO DECEMBER’S QUIZ IS:

B-cell chronic lymphatic leukaemia (B-CLL)

Scattergrams and microscopy

The WDF scattergram showed the presence of conspicuous lymphatic cells located between the lymphocyte and monocyte populations. This would have triggered the ‘Blasts/Abn Lympho?’ flag.
Although abnormal lymphocytes were not visible in the WPC scattergram, a large population of lymphocytes with a high lipid content were observed in the SSC-FSC scattergram of the WPC channel. This resulted in the ‘Abn Lympho?’ flag.
Lymphocytes with a high lipid content were visible as a population of cells with a low side scatter (SSC) and forward scatter (FSC). Blasts were not detected.
PLT-F analysis showed slight thrombocytopenia but with a normal platelet population shape and a normal immature platelet fraction (IPF).
Peripheral blood smear
Peripheral blood smear

Table

Interpretation and Differential Diagnosis

The answer can be inferred from…

  • Lymphocytosis: increased LYMPH# and LYMPH%
  • Presence of malignant lymphocytes: ‘Abn Lympho?’ flag
  • Absence of reactive lymphocytes: no ‘Atypical Lympho?’ flag, no high fluorescence lymphocytes (HFLC)
  • Impaired megakaryopoiesis: mild thrombocytopenia combined with a low immature platelet count (IPF#)

 

Case history

A 61-year old man visited his physician for a routine health check. When the physician detected enlarged lymph nodes she ordered a complete blood count.

Case results

Although WBC counts were normal, an absolute and relative lymphocytosis was observed. In addition, conspicuous lymphocytic cells were detected between the lymphocyte and monocyte populations in the WDF scattergram. In the absence of a WPC channel these cells would have triggered the ‘Blasts/Abn Lympho?’ and ‘Atypical Lympho?’ flags but in this case a WPC reflex measurement was triggered. Blasts were not detected in the flagging areas of the WPC scattergrams but an abnormal ratio of the two lymphocyte populations was visible in the SSC-FSC scattergram: the ‘lower’ lymphocyte population with increased membrane lipids and low forward scatter was comparatively large, indicating the presence of abnormal lymphocytes. This triggered the appearance of the ‘Abn Lympho?’ flag and not the ‘Atypical Lympho?’ flag. In case of reactive lymphocytes, a lower lymphocyte population would have been present in the WPC scattergram as well but always combined with an increased population of reactive lymphocytes in the WDF scattergram. The peripheral blood smear showed the presence of small, abnormal lymphocytes but these cells are very difficult to recognise in an early-phase B-cell chronic lymphocytic leukaemia (B-CLL). No reactive neutrophils or monocytes were observed. Immunotyping using flow cytometry showed a monoclonal CD19 kappa-positive cell clone.

The following answers are incorrect for the described reasons

Healthy individual

Most haematological parameters are normal in this patient and even the mild lymphocytosis may have been induced by a past viral infection. However, the mild thrombocytopenia and low absolute IPF indicate impaired bone marrow activity, and the presence of abnormal, malignant lymphocytes, visible between the lymphocyte and monocyte populations in the WDF scattergram, clearly indicates a pathological condition so this individual is unquestionably sick.

Post-infectious lymphocytosis

The mild lymphocytosis observed here could have been induced by a past infection from which the patient had already recovered. Viral infections trigger an acute phase cellular immune response by the activation of CD8-positive cytotoxic T-cells, CD4-positive T helper 1 cells and natural killer cells as the first cellular defence. This results in a highly increased fluorescence intensity of the lymphocyte population. In the presented case the fluorescence intensity of the lymphocytes is only slightly increased, so both the ‘Blasts/Abn Lympho?’ and ‘Atypical Lympho?’ flags would have been shown if only a WDF measurement (without WPC) would have been performed. Furthermore, the predominant lymphocyte populations in a post-infectious lymphocytosis are CD4-positive T helper 2 cells and activated B-cells (plasma cells), which are activated during the humoral immune response. This would have resulted in a normal fluorescence intensity of the lower lymphocyte population containing T helper 2 cells, and a separate highly-fluorescent population in the WDF scattergram containing the plasma cells. In addition, the population of lymphocytes with low lipid content (the ‘upper’ lymphocyte population in the SSC-FSC scattergram of the WPC channel) would have been bigger. The ‘lower’ lymphocyte population in this patient is comparatively large, so a post-infectious lymphocytosis is unlikely. The presence of abnormal, monomorphic lymphocytes in the presented patient (rather than reactive, atypical lymphocytes) also makes a reactive condition such as a post-infectious lymphocytosis unlikely.

Idiopathic thrombocytopenic purpura (ITP)

ITP is an autoimmune haematological disorder in which autoantibodies against platelet antigens induce accelerated platelet destruction, leading to a reduction in peripheral blood platelets. ITP causes a characteristic purpuric rash and a tendency to bleed, for example from the nose or periodontal gums. It is difficult to distinguish ITP from other causes of thrombocytopenia so diagnosis is a process of exclusion. The presented patient has a mild thrombocytopenia but the normal immature platelet fraction (IPF) and low absolute IPF count (IPF#) indicate a production problem rather than accelerated platelet destruction. In addition, ITP is not associated with the presence of abnormal lymphocytes so it can be excluded here.

Underlying Disease

B-cell chronic lymphocytic leukaemia (B-CLL; 1)

B-CLL is a chronic lymphoproliferative disorder that is probably caused by auto-antigens promoting cell division of B-cell precursors. It is characterised by the presence of uniformly round to somewhat irregular CD5- and CD23-positive B-cells in the peripheral blood. The designation small lymphocytic lymphoma is used when lymphadenopathy is observed, lymphocyte counts are below 5 x 109/L and no cytopenias are observed as a result of bone marrow infiltration. In the presented case the lymphocyte counts are below 5 x 109/L but a thrombocytopenia with reduced megakaryopoiesis was also found, suggesting bone marrow infiltration. Environmental risk factors for B-CLL are not known: risk factors for other types of leukaemia have no proven association with this condition. Genetics, however, is believed to play an important role in B-CLL, which affects Western populations to a much greater extent than far Eastern populations and has a male predominance of 1.5-2 to 1.

 

Classification of lymphoid tumours

Lymphomas are diverse, biologically complex neoplasms of the immune system and comprise approximately 4% of new cancers. Historically, several lymphoma classification schemes have been developed based exclusively on morphologic features but this limited approach has proved unreliable and immunophenotyping, by flow cytometry and/or immunohistochemistry, has emerged as a valuable addition to morphologic diagnosis. By combining light scatter characteristics, patterns of antigen expression and DNA content, flow cytometry provides information that is useful for making a diagnosis and subsequently assessing a prognosis.

Literature

  1. Müller-Hermelink HK, Montserrat E, Catovsky D et al (2007): Chronic Lymphocytic Leukaemia/Small Lymphocytic Lymphoma. In: Swerdlow SH, Campo E, Harris NL, et al (Editors): World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues. 4th Edition. Lyon, France. International Agency for Research on Cancer (IARC) Press: 157-166
  2. Shinton NK (2007): CRC Desk Reference for Hematology, second edition.
  3. Jaffe ES, Harris NL, Stein H et al (2007): Introduction and Overview of the Classification of Lymphoid Neoplasms. In: Swerdlow SH, Campo E, Harris NL, et al (Editors): World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues. 4th Edition. Lyon, France. International Agency for Research on Cancer (IARC) Press: 157-166
  4. Harris NL, Jaffe ES, Stein H et al (1994): A Revised European-American Classification of Lymphoid Neoplasms: a proposal from the International Lymphoma Study Group. Blood 84(5): 1361-1392
  5. The Non-Hodgkin’s Lymphoma Classification Project (1997): A clinical evaluation of the International Lymphoma Study Group classification of Non-Hodgkin’s Lymphoma. Blood 89(11): 3909-3918
  6. Cogliatti SB, Schmid U (2002): Who is WHO and what was REAL? Swiss Med Wkly 132(43-44): 607-617

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