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Keywords:

  • angioimmunoblastic;
  • CXCL13;
  • peripheral T-cell lymphoma;
  • bone marrow

Summary

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Bone marrow (BM) biopsy is often performed early in the evaluation of patients with angioimmunoblastic T-cell lymphoma (AITL), and may be the first diagnostic tissue sample; yet the BM histopathology associated with this disease has not been well described. In this study, BM specimens from 13 patients with AITL were reviewed. Seven (54%) were involved by AITL, which was characterised by paratrabecular and interstitial polymorphous infiltrates containing cytologically atypical lymphocytes, histiocytes and eosinophils. The neoplastic cells were positive for CD10 and CXCL13 by immunohistochemistry in a subset of cases. As in lymph nodes, the lymphomatous infiltrate in some BMs contained numerous small or scattered large B cells, resembling either benign lymphoid aggregates or T cell rich large B cell lymphoma, respectively. Secondary haematological changes were frequent and presented independent of BM involvement by AITL; these included trilineage haematopoietic hyperplasia and plasmacytosis. When BM biopsy preceded the diagnosis of AITL, these secondary changes were misinterpreted as chronic myeloproliferative disease (n = 2), or plasma cell dyscrasia (n = 2). In two cases, these changes obscured the presence of BM involvement by AITL. The spectrum of BM findings in AITL patients is important to recognise for early and accurate diagnosis in this disease.

Angioimmunoblastic T-cell lymphoma (AITL) often presents with a confusing clinical picture, as a systemic illness characterised by B symptoms, generalised lymphadenopathy, hepatosplenomegaly, polyclonal hypergammaglobulinemia, skin rash and haematological abnormalities in the peripheral blood (Jaffe & Ralfkiaer, 2001; Dogan et al, 2003). These protean manifestations can lead to a broad differential diagnosis including systemic infection, autoimmune disease and primary bone marrow (BM) disorders. Lymph node biopsy is typically required to establish the diagnosis of AITL, as the histological changes in this tissue are pathognomonic (Dogan et al, 2003). However, BM biopsy is frequently performed early in the evaluation of these patients and may precede the procurement of a diagnostic lymph node specimen. Although BM involvement in AITL is reportedly frequent (60–90% of patients) (Ghani & Krause, 1985; Gaulard et al, 1991; Merchant et al, 2006), the histopathological features have not been well described. Secondary haematological changes also appear to be common in AITL as might be expected from the systemic nature of this disease, and these also remain poorly characterised.

A number of recently published studies have further delineated the biological properties of the neoplastic T cells of AITL. Many of these properties, such as the expression of CD10 and the follicular chemokine CXCL13, are distinctive for this lymphoma subtype, and establish a link to a normal T-cell subset, the follicle centre T-helper cell (Attygalle et al, 2002; Grogg et al, 2005, 2006; DuPuis et al, 2006, ). In this study, the peripheral blood and BM features of a group of 13 patients with AITL were reviewed with two aims: to provide a more complete description of the peripheral blood and BM features of this disease, and to ascertain if the neoplastic cells in the BM showed immunophenotypic features similar to those described in lymph node specimens.

Materials and methods

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Peripheral blood smears and BM aspirate smear and core biopsy specimens from 13 patients with AITL in the Mayo Clinic pathology files were reviewed. The diagnosis of AITL was documented on lymph node biopsy in each case, either preceding or following the BM specimen. The sets of lymph node and BM specimens were obtained from an approximate 10-year period.

Immunohistochemical stains were performed on the paraffin-embedded BM core biopsies and lymph node specimens according to previously described techniques (Kurtin et al, 1999) with antibodies to CD3 (Clone PS1; Novocastra, Newcastle upon Tyne, UK), CD5 (Clone 4C7; Novocastra), CD10 (Clone 56C6; Novocastra), CD23 (Clone BU38; The Binding Site, San Diego, CA, USA), CD20 (Clone L26; Dako, Carpinteria, CA, USA), CXCL13 (Clone 53610; R&D Systems, Minneapolis, MN, USA), CD138 (Clone M115; Dako) and kappa and lambda immunoglobulin light chains(Polyclonal; Dako). In situ hybridisation studies were performed on paraffin sections of the BM core biopsies in each case using probes specific for Epstein–Barr virus (EBV)-encoded RNA (EBER) according to published methods (Chang et al, 1992).

The Mayo Foundation Institutional Review Board approved this study.

Results

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Paraffin-embedded lymph node biopsies from each of the study cases biopsied were reviewed and confirmed the accepted morphological and immunophenotypic criteria for the diagnosis of AITL (Jaffe & Ralfkiaer, 2001). In each case, the lymph node architecture was partially effaced by a polymorphous paracortical infiltrate, consisting of lymphocytes, immunoblasts, plasma cells, eosinophils and histiocytes. Frequently, the neoplastic CD3 and CD5 positive T cells were present in a perifollicular or perivascular distribution and possessed abundant clear cytoplasm. The cytologically atypical T-cell population was CD10-positive in seven of 10 lymph nodes tested, and co-expressed the follicular chemokine CXCL13 in five of eight cases that had material available for retrospective immunostaining. The CD20-positive B cells present consisted of few to frequent numbers of small to medium-sized cells often associated with depleted lymphoid follicles, as well as large immunoblasts in the expanded paracortex. All lymph node specimens showed a proliferation of follicular dendritic cells (FDCs), which were CD23 positive in the 10 cases stained with this antibody. Significantly increased numbers of EBV-positive immunoblasts was observed in four of nine lymph nodes evaluated by in situ hybridisation, with an additional three of the nine lymph node specimens containing rare EBV-positive cells.

Of 13 BM specimens, seven (54%) were involved by AITL (Table I); a distinctly paratrabecular pattern of involvement was seen in five of these cases (Fig 1). In all cases there were vaguely nodular and poorly circumscribed polymorphous BM infiltrates that included cytologically atypical lymphocytes, histiocytes and eosinophils, with associated reticulin fibrosis (Fig 2A and B). The histiocytic component of the infiltrate varied, and in one case was more prominent, giving a vague granulomatous appearance. These histological features of the BM infiltrates were similar to those seen in the corresponding lymph nodes. Of the seven cases with lymphomatous BM involvement, four were known to show CD10 expression by the lymphoma in the corresponding lymph nodes; two of these specimens showed similar CD10 expression in the lymphomatous BM infiltrates (Cases 1, 6; Fig 2C). Although in many of these cases the status of CXCL13 expression in the lymph node was unknown, the large majority (90%) of AITL cases have been shown to express this marker (Grogg et al, 2005, 2006; DuPuis et al, 2006). Therefore it was not surprising that all six of the bone marrow specimens involved by lymphoma and stained for CXCL13 showed at least focal positivity in cytologically atypical cells (Fig 2D). Although it was not confirmed that CXCL13 staining was present in T cells by double immunostaining techniques, expression of this chemokine is limited to follicle centre T-helper cells and FDCs. The possibility that the CXCL13 positive cells were FDCs was excluded by morphology as well as the lack of significant staining for CD23 in any of the BM specimens.

Table I.   Bone marrow findings in 13 patients with AITL.
 AITL known before BM biopsyOriginal BM diagnosisDiagnosis after reviewPatternCD10CXCL13EBVOther findings
  1. AITL, angioimmunoblastic T-cell lymphoma; BM, bone marrow; PT, paratrabecular; RS, ringed sideroblasts; PRCA, pure red cell aplasia; CMPD, chronic myeloproliferative disorder; HES, hypereosinophilic syndrome; AEC, absolute eosinophil count (×109/l); NA, not applicable; ND, not done.

  2. *Negative in corresponding lymph node.

  3. †Status unknown in corresponding lymph node.

 1YesAITL (50%)SamePT++Clusters of small/medium size B cells, with kappa-predominance, 5% plasma cells
 2YesAITL (10%)SameNodular, focal PT+1–3% RS
 3NoPRCA, negative for lymphomaPRCA, AITL (10%)Interstitial, nodularRare+–*Scattered large B immunoblasts
 4YesAITL (5%)SameNodular, focal PT–*ND*ND† 
 5YesAITL (40%)SameNodular, PT++†ND*51% plasma cells, scattered large B immunoblasts, 5% RS
 6NoMultiple myelomaAITL (20%), reactive plasma-cytosisNodular++Rare+Large B immunoblasts, 37% plasma cells
 7NoNegative for lymphomaAITL (5%)Nodular, PTND†Rare+†ND†Moderate numbers of small B cells, rare large B cells, 15% plasma cells
 8NoCMPDReactive hyper-cellular marrowNA–*Granulocytic and megakaryocytic hyperplasia
 9NoHESReactive eosino-philiaNA–*–*Rare+Panhyperplasia with 20% eos, AEC 37
10NoNegative for lymphomaSameNARare+7% plasma cells with strong CD20
11YesNegative for lymphomaSameNAND 
12YesNegative for lymphomaSameNAND†Rare+†ND† 
13NoAtypical plasma-cytosisReactive plasma-cytosisNAND†–†ND†20% plasma cells
image

Figure 1.  The polymorphous lymphomatous infiltrate had a propensity for a paratrabecular distribution in the bone marrow (Case 7). Original magnification ×200.

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image

Figure 2.  (A) Interstitial bone marrow infiltrates by angioimmunoblastic T-cell lymphoma showing characteristic polymorphous mixture of atypical lymphoid cells, histiocytes and eosinophils (Case 6). (B) An immunostain for CD3 highlighted a T-cell population with irregular nuclear contours. (C) An immunostain for CD10 highlighted an atypical lymphocyte population that corresponded to the CD3-positive T cells. The lymph node from this patient also demonstrated abnormal numbers of CD10 positive cells (not shown). (D) An immunostain for the follicular chemokine CXCL13 stains atypical lymphoid cells corresponding to the CD10, CD3 positive subset. A cluster of atypical cells is seen in the inset. (E) An immunostain for CD20 demonstrated scattered medium to large-size B cells in the infiltrate. (F) Rare cells showed nuclear positivity for EBV within the infiltrate by in situ hybridisation studies. The lymph node from this patient also showed increased numbers of EBV-positive cells (not shown). (G) An immunostain for CD138 demonstrated the increase in plasma cells within the bone marrow (51% of cellularity by aspirate differential count). These plasma cells were polyclonal by immunophenotyping studies. Note the even distribution throughout the bone marrow, with relative exclusion of plasma cells from the area of lymphomatous infiltrate (left). Panels A–G, original magnification ×100.

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As in lymph nodes, the nodular infiltrate in some BM cases contained moderate numbers of small B cells or scattered large B immunoblasts (Fig 2E). The prominence of B cells in these infiltrates might be misconstrued as either benign lymphoid aggregates or T-cell rich large B cell lymphoma, respectively. Indeed, two of the involved cases were initially misinterpreted as negative for lymphoma due to the polymorphous nature of the lymphoid infiltrate and the presence of numerous B cells. Of four cases known to have increased EBV-positive cells in lymph node specimens, only one showed rare EBV-positive cells within the lymphomatous infiltrate in the BM (Case 6, Fig 2F). An additional case without definite BM involvement by lymphoma contained rare EBV-positive cells in the BM (Case 9).

Anaemia was the most common peripheral blood abnormality, present in nine of 13 patients (69%). It was more common, as well as more severe, in patients with BM involvement by AITL compared with those without marrow involvement (Table II). Other peripheral blood abnormalities including neutrophilia, lymphopenia and thrombocytopenia were present in 40–50% of patients regardless of whether or not the lymphoma involved the bone marrow.

Table II.   Peripheral blood findings (A) and secondary bone marrow changes (B) in AITL patients with and without marrow involvement by lymphoma.
Number of patients (n)Involved BMUninvolved BM
76
  1. Hb, haemoglobin; ANC, absolute neutrophil count; ALC, absolute lymphocyte count.

(A) Peripheral blood findings
 Hb (g/l), median (range)93 (83–125)117 (96–140)
  Hb<120 g/l, n (%)6 (86)3 (50)
 ANC (×109/l), median (range)3·9 (1·2–14·7)7·6 (3·0–14·1)
  ANC<1·7 × 109/l, n (%)1 (14)0 (0)
  ANC>7·0 × 109/l, n (%)3 (43)3 (50)
 Lymphocyte count (×109/l), median (range)1·3 (0·34–2·10)1·24 (0·25–3·25)
  ALC<0·9 × 109/l, n (%)3 (43)3 (50)
 Platelet count (×109/l), median (range)172 (21–285)170 (109–477)
  Platelet count <150 × 109/l, n (%)3 (43)1 (17)
 Circulating plasma cells present, n (%)3 (43)1 (17)
(B) Secondary bone marrow changes
 Hypercellular marrow, n (%)6 (86)5 (83)
 Increased erythroid precursors, n (%)4 (57)2 (33)
 Increased granulocytic precursors, n (%)6 (86)4 (67)
 Increased eosinophilic precursors, n (%)3 (43)1 (17)
 Increased megakaryocytes, n (%)4 (57)4 (67)
 Increased plasma cells, n (%)4 (57)3 (50)

Secondary changes in the haematopoetic marrow were present independent of lymphomatous BM involvement (Table II). These changes usually resulted in hyperplasia of one or more marrow elements. Erythroid hyperplasia was more frequent in patients with lymphomatous BM involvement, corresponding to the greater frequency of anaemia in this group. Polyclonal plasmacytosis was common in the BM of both those involved (four of seven) and uninvolved (three of six) by AITL, and was extreme at times (up to 51% of cellularity, average 20%). The plasma cells were evenly distributed throughout the BM, and in fact were relatively excluded from the lymphomatous infiltrates (Fig 2G). These findings were associated with circulating plasma cells in three cases. When BM biopsy preceded the diagnosis of AITL (n = 7), these secondary changes led to a number of misinterpretations including a chronic myeloproliferative disorder (n = 2) and atypical plasmacytosis/plasma cell dyscrasia (n = 2). One patient had pure red cell aplasia in addition to lymphomatous BM involvement (Case 3).

Discussion

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The diagnosis of AITL requires a lymph node biopsy for the assessment of architectural, cytomorphological and immunophenotypic features (Jaffe & Ralfkiaer, 2001), and often confirmation of T-cell clonality by molecular genetic studies. However, patients with AITL commonly present with a systemic illness and haematological abnormalities, leading to a BM biopsy as the first diagnostic procedure. Familiarity with the spectrum of BM changes found in patients with AITL is thus crucial to allow for recognition and early, accurate diagnosis.

Only a few previous reports have described the pathological features of BM involvement by peripheral T-cell lymphomas, and even fewer have included specific features of BM involvement by AITL. In our series of 13 AITL patients, 54% had lymphomatous BM involvement, a frequency similar to previous reports that range from 60–90% (Pangalis et al, 1978; Diebold et al, 1984; Ghani & Krause, 1985; Gaulard et al, 1991; Attygalle et al, 2004; Merchant et al, 2006). The composition of the lymphomatous infiltrate was similar to that seen in involved lymph nodes, consisting of a polymorphous cell population including small lymphocytes, histiocytes, immunoblasts, eosinophils and plasma cells. Three previous reports have noted a paratrabecular distribution (Pangalis et al, 1978; Attygalle et al, 2004; Merchant et al, 2006), with another study describing a ‘granulomatoid appearance with clusters of prominent epithelioid cells’ as the predominant pattern (Ghani & Krause, 1985). We found that a paratrabecular distribution in the marrow with associated reticulin fibrosis was typical in AITL, being seen at least focally in five of seven (71%) involved BMs. The histiocytic component of the infiltrate varied, and in one case was more prominent, giving a vague granulomatous appearance.

Recent studies have provided evidence that the germinal centre T-helper cell represents the normal counterpart to the neoplastic cell of AITL, based on similar gene and protein expression patterns, which include frequent expression of both CD10 and the follicular chemokine CXCL13 (Attygalle et al, 2002; Grogg et al, 2005, 2006; DuPuis et al, 2006). Immunohistochemical detection of these proteins in lymph node specimens has proven diagnostically useful. Attygalle et al (2004) also evaluated the expression of CD10 in the neoplastic cells of AITL involving extranodal sites, and found that CD10 expression was retained in many extranodal sites with the exception of the BM, where it was seen in only one of six cases. Our findings were similar, with only two cases showing CD10 expression in the involved BM. While Attygalle et al (2004) noted an association with FDCs in the case retaining BM CD10 expression, we did not find definite morphological or immunophenotypic evidence of FDCs in the lymphomatous infiltrates containing CD10-positive cells. Immunohistochemical staining for CXCL13 appeared to be more useful for characterisation of AITL in the bone marrow, although the staining was often focal, with the atypical CXCL13-positive cells usually representing a minor component of the polymorphous infiltrate. This feature may limit the diagnostic utility in bone marrows compared to lymph node biopsies. It should also be noted that expression of CD10 and CXCL13 in reactive BM T-cell infiltrates has not been extensively studied.

Another common feature in lymph nodes involved by AITL is the presence of increased numbers of EBV-infected cells. In contrast, this was not a common finding within the lymphomatous infiltrate in the BM, being definitively seen in only one case. Thus, although CD10 and CXCL13 expression, FDC proliferation, and increased numbers of EBV-infected cells are important elements in establishing a diagnosis of AITL in lymph nodes, they are less useful in recognising BM involvement by this disease. Rather, the characteristic polymorphous paratrabecular infiltrate with associated reticulin fibrosis should suggest AITL even in the absence of an established lymph node diagnosis, although a lymph node biopsy is still necessary for most precise lymphoma classification.

AITL is unique among peripheral T-cell lymphomas in that numerous B cells can be present in involved lymph nodes (Dogan et al, 2003; Dogan & Morice, 2004). These B cells are present in some cases within hyperplastic or regressed lymphoid follicles, and in others as numerous immunoblast-like or Reed-Sternberg-like cells in the interfollicular zones. The interfollicular B cells usually correspond to the EBV-infected population, and in some cases an EBV-driven B-cell lymphoproliferative disorder can arise from this population. As in the lymph node, we observed that the AITL infiltrate in the BM could contain moderate numbers of small B cells in nodular aggregates, or scattered immunoblast-like B cells. Without an established diagnosis of AITL, these findings can lead to misinterpretation of BM AITL infiltrates as benign lymphoid aggregates or T-cell rich large B-cell lymphoma respectively. This again emphasises the importance of recognising features that suggest BM involvement by AITL, including the presence of cytologically atypical T cells, which would not be found in either benign lymphoid aggregates or large B-cell lymphomas with a prominent host response.

The secondary bone marrow changes that can occur in the setting of AITL have not been emphasised in the literature. The most frequent changes seen include hyperplasia of the haematopoietic precursors, and polyclonal plasmacytosis. We observed these changes in AITL patients both with and without lymphomatous BM involvement. The precise mechanisms of these alterations in haematopoiesis are unclear, but are probably a reflection of elevated systemic levels of cytokines that have been demonstrated in AITL patients (Foss et al, 1995; Yamaguchi et al, 2000). Regardless of the underlying physiologic mechanisms, it is important to recognise the occurrence of these reactive changes in AITL, to avoid misinterpretation as chronic myeloproliferative disease or multiple myeloma.

Bone marrow evaluation in one patient led to a diagnosis of pure red cell aplasia (PRCA). Subsequent lymph node biopsy from this patient established a diagnosis of AITL, and BM involvement by lymphoma was determined retrospectively. A few cases of AITL with PRCA have been reported (Lynch et al, 1994; Higuchi et al, 1996; Tsujimura et al, 1999). In the study by Tsujimura et al (1999), serum from the patient was shown to inhibit growth of cultured CD34-positive progenitor cells before, but not after, chemotherapy, consistent with a humoral factor causing inhibition at the stem cell level. Although the development of PRCA in this disease is rare, AITL should be included in the differential diagnosis of patients presenting with PRCA.

In conclusion, although the BM is frequently involved by AITL, the histological features are subtle and may be obscured by secondary changes in haematopoiesis that are common. Given the complex clinical manifestations of AITL, which often lead to early BM examination, it is important to recognise the morphological and immunophenotypic features that characterise this disease in the BM biopsy specimen.

Acknowledgements

  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

This research was supported in part by the University of Iowa/Mayo Clinic Lymphoma Specialized Program of Research Excellence (SPORE P50 CA97274). Presented at the United States and Canadian Academy of Pathology Annual Meeting in San Antonio, Texas, 2005.

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  1. Top of page
  2. Summary
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
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