'Hairy' cell leukaemia (leukaemic reticuloendotheliosis): a scanning electron microscopic study of eight cases

Hairy Cell Leukemia Presenting with Isolated Skeletal Involvement Successfully Treated by Radiation Therapy and Cladribine: A Case Report and Review of the Literature

We describe an unusual case of hairy cell leukemia (HCL) in a 55-year-old male presenting with isolated skeletal disease as the initial manifestation without abnormal peripheral blood counts, bone marrow involvement, or splenomegaly. To the best of our knowledge, there have been only two previous reports of a similar case. The patient presented with pain in the right femur. Anteroposterior radiographs of both femurs revealed mixed lytic-sclerotic lesions. PET scan showed multiple metastatic lesions on axial skeleton, pelvis, and both femurs. Histopathological examination of the bone biopsy revealed an infiltrate of HCL. Localized radiation therapy to both proximal femurs and subsequently 4 weeks later, a 7-day course of 0.1 mg/kg/day cladribine provided complete remission with relief of symptoms and resolution of bone lesions. We addressed the manifestations and management of HCL patients with skeletal involvement.

Clinical features and diagnosis of hairy cell leukemia

Significant advances in the diagnosis and treatment of hairy cell leukemia (HCL) have recently been made. Improved distinction of HCL from its mimics though clinical presentations, morphologic and immunophenotypic features, and more recently molecular biology, has highlighted marked differences in treatment response and overall prognosis between these disorders. As our understanding of the unique pathobiology of HCL has grown, exciting new avenues of treatment as well as insight into immune function have been obtained. This review provides an overview of the clinical features and diagnostic attributes of HCL, with contrast to other mature B cell lymphoproliferative disorders with overlapping features.

Hairy cell leukemia and allied chronic lymphoid leukemias: current knowledge and new therapeutic options

This review deals mainly with the essentials of hairy cell leukemia (HCL) detailing clinical aspects, laboratory findings and morphology. Rare manifestations of HCL are listed. Newer aspects relating to cytokines, soluble interleukin receptors and TNF are reviewed. Differential diagnosis including HCL-variant, SLVL, PLL and CLL/PLL are discussed. Prognostic factors and in particular therapeutic aspects are detailed with particular emphasis on the new purine analogues Pentostatin and 2-CdA. A list of suggested reading is offered.

Intractable chronic lymphocytic leukemia and interferon

The hypothesis that interferon may be useful for intractable chronic lymphocytic leukemia (CLL) is based on two incidental findings: first, the similarity in the in vitro radioresistance of the blood lymphocytes of intractable CLL and of hairy cells; secondly, the similarity of the incidence of intractable CLL patients and the incidence of CLL patients who respond to interferon treatment.

Hairy cell leukemia. Electron microscopic observations of two cases

Electron microscopic studies were done on two cases of hairy cell leukemia. Although scanning electron microscopy did reveal typical features of hairy cells, in most abnormal cells, transmission electron microscopy clearly showed that there are two distinct types of cell populations. These two types of leukemic cells with respective lymphoid and non-lymphoid characteristics warrant further investigation.

Hairy cell leukaemia: effects of phorbol ester on cell morphology and adherence and comparison with other B-cell neoplasias

This report documents phorbol ester-induced changes in cell morphology in 9 patients with hairy cell leukaemia (HCL) and contrasts them with those obtained in cells from 20 patients with B-type chronic lymphocytic leukaemia (CLL) and non-Hodgkin's lymphoma in leukaemic phase (NHL). The phorbol ester caused hairy cells to adhere strongly and produce thin elongated cytoplasmic extensions. Other cells showed marked surface ruffling, and contained increased numbers of phagolysosomes, although cells still retained ribosomal lamellar complexes. This in vitro growth pattern differed from that observed in B-CLL and NHL cells, which readily detached in clumps with minimal adherence. CLL and NHL-cells did not show macrophage features but developed plasmacytoid and hairy cell-like features. It is suggested that these different growth patterns may aid in distinguishing HCL from other B-cell neoplasias.

Cytochemistry and ultrastructure in lymphoma and leukemia: utility in the diagnosis of different leukemias and the recognition of subtypes of lymphoproliferative disorders

This review is based on the findings of multiparameter studies performed on cells obtained from over 200 cases of leukemia and illustrates the wide range of laboratory tests currently available for cell phenotype identification. Immunological techniques are not discussed and the review deals mainly with light and electron microscopic cytochemistry, transmission (TEM) and scanning electron microscopy (SEM). The importance of light microscopic cytochemistry is clearly demonstrated. In particular, paranuclear acid phosphatase, non-specific esterase (NSE) and diaminopeptidase staining are recommended as reliable T-cell markers. Ultrastructural identification of unclassified leukemic cells using techniques to detect myeloperoxidase, acid phosphatase, platelet peroxide (PPO) and NSE, is shown to be of great importance in cases of early myelo-monoblastic differentiation with negative light microscopic cytochemistry. SEM is also shown to be a reliable means of distinguishing lymphoid and non-lymphoid leukemia when some degree of differentiation is present. However SEM does not appear to contribute in the diagnosis of unclassified leukemia. The new scanning immunoelectron microscopy (SIEM) technique employing heteroantisera or monoclonal antibodies conjugated to latex microspheres (immunolatex) to detect surface receptors and specific antigens is also illustrated. This technique displays the topography of surface antigens on the cell surface of leukemic cells in 3-dimension and facilitates simultaneous visualization of the surface architecture of the labelled cells.

Phagocytic capacity of hairy cells from seventeen patients

Hairy cells from 17 patients diagnosed as having hairy cell leukemia were evaluated with both light and transmission electron microscopy for their capacity to phagocytose zymosan, latex, Staphylococcus aureus, and Pseudomonas aeruginosa. The hairy cells of fifteen of the sixteen patients which were tested with latex showed significant phagocytosis. Cells of thirteen of the seventeen patients showed phagocytosis of staphylococcus; six of the seventeen, phagocytosis of zymosan; and four of seventeen, phagocytosis of pseudomonas. Of the four substances tested, staphylococcus and latex yielded consistently higher numbers of ingested particles per hairy cell than did zymosan or pseudomonas. Observation of serial sections by transmission electron microscopy revealed that each type of particle is fully enclosed within the cytoplasm of the hairy cell. A Lysostaphin assay performed on the hairy cells of two patients showed that lysis of the phagocytosed particles by the hairy cell differs significantly from that by normal mononuclear cells. The results support our earlier study which suggested that hairy cells have phagocytic capabilities which differ not only among patients, but also within a single patient over time.

The contribution of scanning electron microscopy in haematology: its role in defining leucocyte and erythrocyte disorders

This report reviews the contribution of scanning electron microscopy (SEM) in haematology. Important observations regarding red cell shape and deformities are referred to and contributions in the definition and classification erythrocyte disorders are stressed. In this field there is no doubt that SEM has contributed much to the three-dimensional visualization of RBC disorders. As far as leucocyte pathology is concerned the situation is less clear. SEM has contributed much to current knowledge and understanding of the surface properties of white blood cells. Normal leucocytes have different surface features and can be distinguished under the SEM. However, some overlap does occur, making individual distinction on the basis of surface architecture alone extremely difficult. The difficulties in this regard are discussed in this review and factors influencing the variability of surface microprojections are reviewed briefly. Leukaemic cells of different origins may also be distinguished under the SEM. However, while "hairy' cells have typical surface features and non-lymphoid leukaemic cells, in particular monocytes, are readily distinguished from lymphoid leukaemic cells, there is much overlap of surface topography. Undifferentiated cells and early myeloblasts and lymphoblasts have similar surface features and cannot be distinguished under the SEM. While SEM adds a valuable third dimension to morphology and ultrastructure, it cannot be used alone in the definition of difficult cases of acute leukaemia.

Surface immunoglobulin, lectin-induced cap formation, and phagocytic function in five patients with the leukemic phase of hairy cell leukemia

Hairy cells from 5 patients with greater than 25% hairy cells in the peripheral blood (4 had greater than 45% hairy cells and white blood cell counts (WBC) greater than 10,000/mm3) were studied for surface immunoglobulin (SIg) presence and distribution by two methods, for lectin-induced cap formation, and for phagocytosis of zymosan. Hairy cells from all 5 cases were found to have distinct monoclonal patterns, 2 Gk, 1 MDk, 1 Dk, and 1 GMDk, as well as cap formation with SIg. All 5 cases showed distinct lectin-induced cap formation in a percentage of cells similar to the percentage of hairy cells, and 2 of the 5 patients had hairy cells which phagocytosed zymosan. These findings contrasted with the malignant cells from 4 patients with CLL, which had monoclonal SIg but no SIg cap formation and no significant percentage of lectin-induced cap formation. Cells from 2 cases of T cell lymphomas had no SIg and no lectin-induced cap formation as did cells from 2 cases of non-lymphocytic leukemia. Hairy cells not only appear to have SIg cap formation similar to some B-lymphocytes, which in some patients also phagocytose zymosan, but also demonstrate strong lectin-induced cap formation.

Hairy cell leukemia: differences in phagocytic capacity of cells in vitro

Hairy cells from eight patients with hairy cell leukemia were evaluated with both light and transmission electron microscopy for their capacity to phagocytose zymosan, latex, staphylococcus aureus, and pseudomonas aeruginosa. In two patients, there was no phagocytosis of any of these substances; cells from three patients phagocytosed only latex; two, all except pseudomonas; and one, all 4 substances. Hairy cells became relatively smooth while in culture with staphylococcus, but no surface changes were noted during incubation with the other substances. Of the eight patients studied, one died of pseudomonas pneumonia and sepsis; pseudomonas was the only substance which her hairy cells did not phagocytose. The one patient whose hairy cells phagocytosed all 4 test substances developed a disseminated Mycobacterium intracellulare infection; culture of his hairy cells with this atypical myocbacterium showed no phagocytosis. Hairy cells have different phagocytic capabilities from patient to patient, and the evaluation of these capabilities in vitro might provide early identification of potential infectious complications.

Hairy cell leukemia: an autopsy study

Autopsy material from 5 patients with hairy cell leukemia was examined. In addition to the expected widespread involvement of the hematopoietic system and of the liver, all of the patients had various amounts of pulmonary infiltration by leukemic cells. This infiltration was so severe in one instance that the resulting pulmonary insufficiency was the cause of death. Other areas of hairy cell infiltration included the peripancreatic connective tissue in all cases, kidneys in 3 cases, pericardium in 2 cases, and skin in 1 case. Association of plasma cells with the infiltrating neoplastic cells was prominent. In one patient, foci of large, bizarre cells were found in several lymph nodes and in the pericardium. Whether these cells represent transformation of the hairy cells into a larger, less differentiated cell type, or the emergence of a second hematopoietic neoplasm, is unknown.

Hairy cell leukemia: an analysis of the chromosomes of 26 patients

We studied the chromosomes from 26 patients with hairy cell leukemia (HCL) to ascertain the frequency and types of consistent chromosomal abnormalities. Samples from 21 patients were obtained from peripheral blood cultures grown 24 and 48 h without phytohemagglutinin, or from bone marrow samples. Two male patients had similar, consistent abnormalities; one patient's karyotype was 46, X, +12; that of the second was 46, X, +C marker. In the latter case, the distal long arm of the C marker most closely resembled chromosome No. 12 from band q14 to q terminal, but the short arm and proximal long arm were of undetermined origin. Both karyotypes lacked the Y chromosome. Nine of the 21 patients had abnormalities in single cells. One patient had, in one sample, a single abnormal cell with an extra No. 3 and an extra No. 12 (48, XY, +3, +12), and in a later sample, a second cell of poor morphology which also could have been trisomic for No. 12. Another patient had one cell with an unusually bright short arm, as well as two cells, with different abnormalities, both involving the short arm of chromosome No. 1. The two patients with consistent chromosome abnormalities had rapidly progressive disease in spite of splenectomy, and their clinical course from the time of diagnosis was relatively short (5 and 7 months, respectively).

Hairy cell leukemia: an unusual lymphoproliferative disease: a study of 24 patients

A laboratory and clinical evaluation of 24 patients with hairy cell leukemia was carried out over a 23-month period. Most patients had splenomegaly without adenopathy or pancyotpenia. Nine of the patients had undergone splenectomy prior to referral; their median WBC count was 6600/mm3. The median WBC count for the 14 patients who had no prior therapy was 3550/mm3, and their median platelet count was 80,500/mm3. Spleen weights ranged from 618 to 3780 g; there appeared to be no relationship between the size of the spleen and the response in the blood counts after splenectomy. Four patients in whom the majority of the WBC were hairy cells underwent splenectomy, which produced no real change in their WBC count; however, there was improvement in the platelet count in three. In contrast, the presence of leukopenia with a low percentage of hairy cells predicted a beneficial response to splenectomy. The study of surface immunoglobulins (SIg) in 16 patients demonstrated that resynthesis had occurred in each case. Phagocytosis of zymosan was studied in 15 patients; in 8 of these, 25% or more of the hair cells were capable of phagocytosis; in 6 others, 0--9%; and in one, 13%. The resynthesis of SIg is a feature usually associated with B-lymphocytes, but the phagocytosis of zymosan is not. Thus, the existence of either a spectrum of functional capabilities of hairy cells or several distinct subtypes is suggested by these data. Platelet aggregation with epinephrine was abnormal in 7 of 14 patients studied but there were no clinically significant bleeding problems. A chromosome abnormality was present in 2 of the 19 patients from whom adequate samples were obtained; the abnormality probably involved chromsome 12 in both patients as well as absent Y and was associated with a rapidly progressive clinical course. The presence of a predominant number of hairy cells with a normal or increased peripheral blood WBC count or of a chromosomal abnormality suggests that splenectomy might not be beneficial as the initial therapy and that chemotherapy should be considered.

Scanning electron microscopy and the surface morphology of human lymphocytes

The surface of the human lymphocyte as seen by the scanning electron microscope shows variations which may reflect the functional state or environment of the cell. Preparative techniques and future developments in this area are reviewed.

Leukemic reticuloendotheliosis: polyclonal surface immunoglobulin on "hairy" cells

The cytochemistry, surface markers and functional properties of purified mononuclear cells obtained from the peripheral blood and spleen of a patient with leukemic reticuloendotheliosis were studied. Nonspecific esterase activity, a monocyte marker, was demonstrable in 83% of the peripheral blood mononuclear cells and 84% of the splenic mononuclear cells. Rosetting techniques failed to detect T or B lymphocyte surface markers on the majority of the cells. Direct immunofluorescence revealed capped, noncytophilic surface immunoglobulin on the cells with all immunoglobulin classes being detectable. Since noncapping conditions ahd been used during immunofluorescence staining, the observed caps were attributed to in vivo binding of autoantibodies to the "hairy" cells. This conclusion was supported by the demonstration of susceptibility of the "hairy" cells to lysis mediated by normal allogeneic lymphocytes. It is postulated that the "hairy" cells in this patient are leukemic monocytes which bear autoantibodies directed against leukemia associated antigens.

Hairy cell leukaemia: seven cases with probable B-lymphocytic origin

Mononuclear cells from seven patients with hairy cells leukaemia were examined for features suggestive of either a lymphocytic or monocytic origin. Immunofluorescent staining of both methanol fixed and incubated cells, using monospecific antisera, revealed a predominant cell-associated immunoglobulin in each case. Three were positive for mu and kappa chains, two for gamma and kappa chains, one for delta and kappa chain determinants and one reacted only with antigamma chain serum. Formation of EAC rosettes, a feature of both B lymphocytes and monocytes, was variable. T cells, as judged by E rosettes, were not elevated in any patient. Phytohaemagglutinin reactivity was normal in six and depressed in one case. With the exception of minimal activity in assays for glass adherence and latex particle phagocytosis, none of the cells showed features typical of monocytes. Hairy cells were negative by peroxidase stain and lacked the electron microscopic characteristics of monocytes. They did not react in either rosette or phagocytic assays with anti-A or anti-D coated erythrocytes nor did they elaborate granulocyte colony stimulating factor, a monocyte-derived in vitro granulopoietin. Although unequivocal classification of these abnormal cells is not possible, the data storngly suggests that this represents a variant of a B lymphocytic neoplasm.

Malignant histiocytosis with chronic course. Ultrastructural and ultrastructural cytochemical studies

Four cases of malignant histiocytosis with leukemic manifestations and chronic course were reported. Light microscopic, ultrastructural and ultrastructural cytochemical details of these atypical cells were demonstrated. Ultrastructurally these cells resembled hairy cells most closely among the known varieties of leukemic cells. However, ribosome-lamella complexes were not found and some atypical cells had a few short cytoplasmic projections. In addition, tartrate-resistant acid phosphatase was absent from these cells. We speculate that this leukemic reticuloendotheliosis with a chronic course seen in Japan seems to be analogous to malignant histiocytosis with massive splenomegaly reported by Vardiman et al.

Hairy cell leukemia. Enzyme histochemical characterization, with special reference to splenic stromal changes

Seven spleens and two peripheral blood specimens from eight patients with hairy cell leukemia were examined with enzyme cytochemical and histochemical methods. Hairy cells consistently exhibited acid phosphatase and tartrate-resistant acid phosphatase. However, nonspecific esterases characteristic of monocytes and histiocytes were consistently absent or very weak. beta-glucuronidase and cytoplasmic membrane-bound ATPase were positive in four cases, suggesting a possible relationship to the B-lymphocytic series. Fundamental splenic changes were accumulation of hairy cells and benign macrophages within the pulp cords, with resulting extreme expansion of the cords. Abnormally well developed ellipsoids were identified around the sheathed arteries within the cords. Sinuses, specifically delineated with the NASDA reaction, were atrophic and often destroyed. No cytogeneologic relationship was found between sinus endothelial cells and hairy cells. The pulp cords are the primary site of involvement of the spleen in hairy cell leukemia. A simultaneous proliferation of neoplastic cells, histiocytes and reticulum fibers accounts for the splenomegaly and clinical hypersplenism characteristic of the disease.

Surface features of Sezary cells: A scanning electron microscopy study of 5 cases

The surface features of circulating cells from 5 patients with typical Sezary's Syndrome (SS) are described using scanning electron microscopy (SEM). Sezary cells prepared by different methods, with and without prior fixation in cell suspension, showed similar surface architectures. SS cells were mostly spherical and moderate to markedly villous in appearance, and in this respect, resembled the majority of circulating lymphocytes from patients with chronic lymphocytic leukaemia (CLL). A proportion of cells were larger and more irregular in shape while others had small extensions of cytoplasm resembling small uropods with clusters of polarised microvilli. Despite the latter findings, most SS cells cannot be distinguished from CLL cells on the basis of their surface architecture under the SEM.

Hairy cell leukemia. An immunologic and ultrastructural study

A case of hairy cell leukemia in a 39-year-old man is reported. Hairy cells from the peripheral blood, spleen, and bone marrow had lambda-type immunoglobulin on their surfaces; those from the peripheral blood and bone marrow also had IgD on their cell membranes. Frozen sections of spleen reacted with IgGEA, but not IgMEA or IgMEAC markers. Transmission electron microscopy revealed ribosome-lamella complexes in cells from the spleen, but not the peripheral blood. Scanning electron microscopy demonstrated a spectrum of cell surface morphology with many cells characterized by ridges and ruffles. The significance of these findings is considered and it is suggested that the hairy cell is a B lymphocyte.

Leukemic reticuloendotheliosis. A failure of monocyte production

In five cases of leukemic reticuloendotheliosis studied, profound monocytopenia was demonstrable. In 48 normal subjects, monocyte counts ranged from 215 to 921 per cubic millimeter, whereas in the five patients with leukemic reticuloendotheliosis, the counts ranged from 0 to 17 per cubic millimeter. The properties of the "hairy" cell are consistent with those of an incompletely developed monocyte. The susceptibility to infection, characteristics of these patients, may result from a lack of normal monocytes in blood and tissues.

Hairy cell leukemia. Bone marrow findings in 24 patients

In 24 patients with hairy cell leukemia, histological and fine structural findings from biopsies of the bone marrow are reported and their validity is compared with other diagnostic procedures available. Diagnosis by light microscopy of anterior iliac crest biopsies obtained by the method of myelotomy is possible with a high degree of accuracy. The differentiation of hairy cell leukemia from other myelo- or lymphoproliferative disorders based on cytomorphology as well as patterns of growth is emphasized. Morphological differences between fibrosis in this entity and other lesions such as malignant lymphomas, Hodgkin's disease, osteomyelofibrosis and -sclerosis are emphasized. Electron microscopy of the bone marrow shows single fibroblastic cells with numerous slender cytoplasmic processes randomly dispersed among the hairy cells. These fibroblasts are probably responsible for the synthesis of the reticulin and collagen fibres in their surroundings. Moreover fine structur of the hairy cells demonstrates pinocytic activity but no apparent phagocytosis in contrast to the phagocytic reticulum cells (histiocytes, macrophages). In the bone marrow the precursor cells and the many immature forms of hairy cells exhibit an overall lymphocytoid appearance during their maturation, suggesting a lymphocytic origin.

Hairy cell leukemia (leukemic reticuloendotheliosis) II. Ultrastructure of the spleen

Seven surgically removed spleens from patients with hairy cell leukemia and hypersplenism were examined ultrastructurally. In all spleens the pulp cords were diffusely and compactly infiltrated by hairy cells. Numerous hairy cells were also evident in the often distended sinuses. The hairy projections were readily visible in electron micrographs and tended to interdigitate to form syncytium-like aggregates. Compression of hairy cells within the cords flattened the projections against the cell bodies and may account for the surface alterations reported by scanning electron microscopic studies. Controversy over the cytogenesis of hairy cells has not been resolved by ultrastructural studies. Although all seven patients had hypersplenism, the hairy cells showed no evidence of phagocytic activity. However, active phagocytosis by cordal macrophages was observed and there is a probable absolute increase in their number contributing to the splenomegaly. The dense infiltrate of hairy cells causes marked widening of the cords and retards the passage of formed elements of the blood through the red pulp. Prolonged sojourn of these elements in a metabolically unfavorable environment results in cellular damage, increased exposure to cordal macrophages, and premature destruction with the evolution of a hypersplenic syndrome.

The effects of preparative procedures for scanning electron microscopy on the size of isolated lymphocytes

The diameter of lymphocytes, isolated from a sample of peripheral blood by Ficoll-Hypaque sedimentation, was determined after eight different steps in the preparative procedure for scanning electron microscopy (SEM). There was a 43% total reduction in mean cellular diameter of the lymphocytes studied, the diameter dropping from 8.4 mum prior to fixation, to a final diameter of 4.8 mum in the cells examined under the scanning electron microscope. The bulk of this shrinkage occurred during critical-point drying. In view of this finding, caution should be exercised in describing detailed cell surface morphology by SEM when similar preparative procedures are employed.

The scanning electron microscopy of normal human peripheral blood lymphocytes

A study of the effects of various sample preparation techniques for scanning electron microscopy has been undertaken in an attempt to resolve conflicting descriptions of the surface topography of human peripheral blood lymphocytes. By fixing cells in suspension--a technique thought most likely to avoid the production of artefacts--no clearly defined morphological classification of lymphocytes could be made, and when T- and B-lymphocyte enriched preparations were studied their surfaces appeared similar. Both T- and B-rosetted cells showed identical morphological changes as a result of their interaction with red blood cells. The smooth cells described in other reports were found only under certain conditions of preparation. It is therefore not possible to distinguish between T- and B-cell populations, using the S.E.M., on the basis of surface morphology alone.

Surface features of cells in human lymphoproliferative disorders. An immunoelectron microscopy study

Peroxidase conjugated antibodies were applied to cell suspensions in order to detect surface associated immunoglobulins. Cell suspensions were fixed prior to incubation with reagents, a procedure avoiding membrane alterations induced by antibodies to surface component. By immunoelectron microscopy an identification of B lymphocytes could be made with simultaneous observation of their surface architecture. Basic findings were that normal circulating human B lymphocytes had a villous surface. This relationship was not confirmed however by examinating samples from various B and T cell proliferations establishing that surface morphology is not sufficient to categorize cells in disease. Specimens from hairy cell leukemia were also examined. Despite salient surface characteristics as revealed by the present method, the categorization of cells remains unclear.

A scanning electron microscopy and immunological study of 84 cases of lymphocytic leukaemia and related lymphoproliferative disorders

The surface features of cells from 84 cases of lymphocytic leukaemia, and related lymphoproliferative disorders are described as seen by scanning electron microscopy (SEM). Most of the 46 cases of CLL were shown to be B-derived, but rare cases of mixed B and T cell leukaemia and leukaemia with cells bearing both B and T markers were also encountered. Despite the existence of a spectrum of cell surface morphology, it was possible in many cases to identify a dominant cell type. Cells from cases of B derived malignancies were most frequently of the 'predominantly villous' type while a smaller proportion of cases were of the predominantly 'smoother' or 'mixed villous and smooth' type. Variations in surface morphology also occurred with progression of the disease. In most cases of acute lymphoblastic leukaemia (ALL) 'smoother' cells predominated. However, more cases of ALL and T derived leukaemia need to be examined before definite conclusions can be drawn concerning the surface of these cell types. This study also illustrates the importance of examining large numbers of cases of leukaemia, before conclusions are drawn concerning their surface features and indicates that SEM cannot consistently distinguish between leukaemic B and T cells. It will be of interest to determine whether the surface architecture of the leukaemic cell is related to the degree of cell differentiation and eventual prognosis in these cases.

A scanning electron microscopic study of 34 cases of acute granulocytic, myelomonocytic, monoblastic and histiocytic leukemia

This report describes the surface architecture of leukemic cells, as seen by scanning electron microscopy in 34 patients with acute nonlymphoblastic leukemia. Six patients with myeloblastic, 4 with promyelocytic, 10 with myelomonocytic, 8 with monocytic, 4 with histiocytic and 2 with undifferentiated leukemia were studied. Under the scanning electron microscope most leukemia histiocytes and monocytes appeared similar and were characterized by the presence of large, well developed broad-based ruffled membranes or prominent raised ridge-like profiles, resembling ithis respect normal monocytes. Most cells from patients with acute promyelocytic or myeloblastic leukemia exhibited narrower ridge-like profiles whereas some showed ruffles or microvilli. Patients with myelomonocytic leukemia showed mixed populations of cells with ridge-like profiles and ruffled membranes whereas cells from two patients with undifferentiated leukemia had smooth surfaces, similar to those encountered in cells from patients with acute lymphoblastic leukemia. It appears that nonlymphoblastic and lymphoblastic leukemia cells (particularly histiocytes and monocytes) can frequently be distinquished on the basis of their surface architecture. The surface features of leukemic histiocytes and monocytes are similar, suggesting that they may belong to the same cell series. The monocytes seem to have characteristic surface features recognizable with the scanning electron microscope and differ from most cells from patients with acute granulocytic leukemia. Although overlap of surface features and misidentification can occur, scanning electron microscopy is a useful adjunct to other modes of microscopy in the study and diagnosis of acute leukemia.