Hematological Manifestations among Patients with Rheumatic Diseases

BACKGROUND

Rheumatic diseases have many hematological manifestations. Blood dyscrasias and other hematological abnormalities are sometimes the first sign of rheumatic disease. In addition, novel antirheumatic biological agents may cause cytopenias.

SUMMARY

The aim of this review was to discuss cytopenias caused by systemic lupus erythematosus and antirheumatic drugs, Felty's syndrome in rheumatoid arthritis, and autoimmune hemolytic anemia, thrombosis, and thrombotic microangiopathies related to rheumatological conditions such as catastrophic antiphospholipid syndrome and scleroderma renal crisis. Key Message: The differential diagnosis of various hematological disorders should include rheumatic autoimmune diseases among other causes of blood cell and hemostasis abnormalities. It is crucial that hematologists be aware of these presentations so that they are diagnosed and treated in a timely manner.

Chronic neutropenia in LGL leukemia and rheumatoid arthritis

This section reviews the diagnostic criteria and pathogenesis of large granular lymphocyte (LGL) leukemia. There is a particular focus on the overlap of LGL leukemia and rheumatoid arthritis (Felty's syndrome). Current understanding of the mechanisms of neutropenia in these disorders is discussed. Finally, treatment indications and therapeutic recommendations are outlined.

The spectrum of large granular lymphocyte leukemia and Felty's syndrome

PURPOSE OF REVIEW

Patients with chronic large granular lymphocyte (LGL) leukemia often have rheumatoid arthritis (RA), neutropenia and splenomegaly, thereby resembling the manifestations observed in patients with Felty's syndrome, which is a rare complication of RA characterized by neutropenia and splenomegaly. Both entities have similar clinical and laboratory presentation, as well as a common genetic determinant, HLA-DR4, indicating they may be part of the same disease spectrum. This review paper seeks to discuss the underlying pathogenesis and therapeutic algorithm of RA, neutropenia and splenomegaly in the spectrum of LGL leukemia and Felty's syndrome.

RECENT FINDINGS

We hypothesize that there may be a common pathogenic mechanism between LGL leukemia and typical Felty's syndrome. Phenotypic and functional data have strongly suggested that CD3 LGL leukemia is antigen-activated. Aberrations in the T-cell repertoire with the emergence of oligoclonal/clonal lymphoid populations have been found to play a pivotal role in pathogenesis of RA. The biologic properties of the pivotal T cell involved in RA pathogenesis are remarkably similar to those in leukemic LGL.

SUMMARY

RA-associated T-cell LGL leukemia and articular manifestations of typical Felty's syndrome are not distinguishable. A common pathogenetic link between LGL leukemia and RA is proposed.

The impact of HLA-DRB1 genes on extra-articular disease manifestations in rheumatoid arthritis

The objective of this study was to examine HLA-DRB1 and HLA-DQB1 genotypes in patients with severe extra-articular rheumatoid arthritis (ExRA) and to compare them with the genotypes of rheumatoid arthritis (RA) patients without extra-articular manifestations. Patients with severe ExRA were recruited from a large research database of patients with RA, from two cohorts of prevalent RA cases, and from a regional multicenter early RA cohort. Cases with ExRA manifestations (n = 159) were classified according to predefined criteria. Controls (n = 178) with RA but no ExRA were selected from the same sources. Cases and controls were matched for duration of RA and for clinical center. PCR based HLA-DRB1 and HLA-DQB1 genotyping was performed using the Biotest SSP kit, with additional sequencing in order to distinguish DRB1*04 subtypes. Associations between alleles and disease phenotypes were tested using multiple simulations of random distributions of alleles. There was no difference in global distribution of HLA-DRB1 and HLA-DQB1 alleles between patients with ExRA and controls. DRB1*0401 (P = 0.003) and 0401/0401 homozygosity (P = 0.002) were more frequent in Felty's syndrome than in controls. The presence of two HLA-DRB1*04 alleles encoding the shared epitope (SE) was associated with ExRA (overall odds ratio 1.79, 95% confidence interval 1.04-3.08) and with rheumatoid vasculitis (odds ratio 2.44, 95% confidence interval 1.22-4.89). In this large sample of patients with ExRA, Felty's syndrome was the only manifestation that was clearly associated with HLA-DRB1*0401. Other ExRA manifestations were not associated with individual alleles but with DRB1*04 SE double dose genotypes. This confirms that SE genes contribute to RA disease severity and ExRA. Other genetic and environmental factors may have a more specific impact on individual ExRA manifestations.

Longterm outcome of treatment of Felty's syndrome with intramuscular gold: case reports and recommendations for management

OBJECTIVE

To evaluate the incidence, complications, and course of Felty's syndrome (FS) in patients treated with intramuscular (IM) gold.

METHODS

Retrospective chart review of all FS cases (1979 to 2003) was conducted in the Mary Pack Arthritis Centre (MPAC) gold clinic. FS was diagnosed if patients had rheumatoid arthritis (RA; American College of Rheumatology criteria) and persistent leukopenia [white blood cell (WBC) count < 4] in the absence of other known causes of leukopenia. Splenomegaly was not part of the inclusion criteria.

RESULTS

Thirteen patients with FS were identified in the gold clinic population. The mean age at diagnosis of FS was 58.7 years and the mean duration of RA at time of diagnosis was 6.9 years. The weekly dose of gold ranged from 10 mg to 50 mg depending on tolerability. Gold therapy resulted in normalization of the WBC count in 9 of 13 patients. The mean time to normalization of the WBC was 40 weeks. Only one patient with FS had experienced recurrent infectious complications from FS, and this did not recur after gold treatment was initiated. No patient had vasculitis.

CONCLUSION

In our gold clinic population FS is a mild disease and is rarely associated with infectious complications. Gold is an effective treatment of FS.

Felty's syndrome

Felty's syndrome (FS) comprises a triad of rheumatoid arthritis (RA), neutropenia and splenomegaly, occurring in less than 1% of RA patients. Clinically it is characterized by severe joint destruction contrasting with moderate or absent joint inflammation and severe extra-articular disease, including a high frequency of rheumatoid nodules, lymphadenopathy, hepatopathy, vasculitis, leg ulcers, skin pigmentation etc. Recurrent bacterial infections are mostly due to the severe, otherwise unexplained neutropenia. The cause of neutropenia lies in both decreased granulopoiesis and increased peripheral destruction of granulocytes. Recurrent infections may lead to increased mortality. Spontaneous remission of the syndrome also occurs. Over 95% of FS patients are positive for rheumatoid factor (RF), 47-100% are positive for antinuclear antibody (ANA), and 78% of patients have the HLA-DR4*0401 antigen. Some 30% of FS patients have large granular lymphocyte (LGL) expansion. LGL expansion associated with uncomplicated RA is immunogenetically and phenotypically very similar to but clinically different from FS. Neutropenia of FS can be effectively treated with disease-modifying anti-rheumatic drugs (DMARDs), the widest experience being with methotrexate (MTX). Results of treatment with granulocyte colony-stimulating factor (G-CSF) are encouraging, but there is no experience with other biological agents. Splenectomy results in immediate improvement of neutropenia in 80% of the patients, but the rate of infection decreases to a lesser degree.

Association of autoantibodies to glucose-6-phosphate isomerase with extraarticular complications in rheumatoid arthritis

OBJECTIVE

In the K/BxN mouse model, autoantibodies against glucose-6-phosphate isomerase (GPI) cause arthritis. The relevance of this model for human disease remains a subject of controversy. We set out to determine whether GPI autoantibodies occur in patients with rheumatoid arthritis (RA) and, if so, at what stage of the RA.

METHODS

Using an enzyme-linked immunosorbent assay, serum from 131 RA patients and 28 healthy controls was tested for autoantibodies against recombinant human GPI. Patients were grouped according to disease duration and presence of rheumatoid nodules, rheumatoid vasculitis, and Felty's syndrome, which are extraarticular complications of RA.

RESULTS

Elevated levels of autoantibodies against GPI were present in 5% of patients with uncomplicated RA and 4% of controls. In RA complicated by extraarticular manifestations, anti-GPI antibodies were observed in 18% of patients with rheumatoid nodules, 45% of patients with rheumatoid vasculitis, and 92% of patients with Felty's syndrome.

CONCLUSION

In patients with RA, autoantibodies to GPI are associated with the occurrence of extraarticular complications.

Pure red cell aplasia in Felty's syndrome: a case report of successful reversal after cyclosporin A treatment

We describe the first report of a patient with Felty's syndrome who developed pure red cell aplasia, likely not attributable to medication, that was successfully treated with cyclosporin A.

Development of rheumatoid arthritis after treatment of large granular lymphocyte leukemia with deoxycoformycin

The association of T-cell large granular lymphocyte (LGL) leukemia and rheumatoid arthritis is well described and it is now recognized that these patients and patients with Felty's syndrome represent different aspects of a single disease process. Most patients have rheumatoid arthritis at the time of diagnosis of LGL leukemia. This is the first detailed report of the development of rheumatoid arthritis after the diagnosis and treatment of LGL leukemia as well as the first report of rheumatoid arthritis that occurred in association with deoxycoformycin treatment. It is likely that the beneficial sustained normalization of neutrophil counts as a result of deoxycoformycin treatment played a significant role in the development of this complication. Hematological improvement occurred despite molecular genetic evidence of persistence of the abnormal T-cell clone. The role of the clonally expanded T cells in the pathogenesis of neutropenia and rheumatoid arthritis is discussed.

[Rheumatoid arthritis, neutropenia and splenomegaly: the Felty syndrome]

HISTORY AND FINDINGS

A 59-year-old asymptomatic man, first diagnosed to have rheumatoid arthritis 27 years ago, was admitted to hospital because of splenomegaly and neutropenia, first noted 2 years ago. Physical examination confirmed splenomegaly and also revealed pretibial hyperpigmentation, but no evidence of active rheumatoid arthritis.

EXAMINATIONS

Biochemical tests showed relative and absolute neutropenia (white blood cell count 2200/microliters; 1% neutrophils), thrombocytopenia and polyclonal hypergammaglobulinaemia. He also had increased erythrocyte sedimentation rate (38/92), a high titre of rheumatic factor (2128 IU/ml) and increased circulating immune-complexes (74%). Thoracic and abdominal computed tomography provided no evidence of malignant tumor. The spleen measured 15 x 7 x 10 cm. Bone-marrow biopsy from the iliac crest revealed abnormal maturation of granulopoiesis and marked lymphoid infiltration. The clinical triad of rheumatoid arthritis, splenomegaly and neutropenia are diagnostic of Felty's syndrome. As the patient was asymptomatic there was no indication for treatment.

CONCLUSION

Felty's syndrome is a rare condition demanding considerable effort in differential diagnosis.

Hematologic and cytofluorographic analysis of patients with Felty's syndrome. A hypothesis that a discrete event leads to large granular lymphocyte expansions in this condition

OBJECTIVE

To compare hematologic and cytofluorographic features in Felty's syndrome (FS) patients with and without the large granular lymphocyte (LGL) syndrome.

METHODS

Peripheral blood cells from FS patients and from 2 control groups (rheumatoid arthritis [RA] patients and subjects without symptoms of a rheumatic disease) were analyzed by hematologic and cytofluorographic techniques. A separate assessment of disease activity was performed.

RESULTS

FS patients had reduced lymphocyte and platelet counts, with a parallel reduction in lymphocyte subsets examined. CD4 counts were reduced in all FS patients, including those with the LGL syndrome. Disease activity was lower in FS patients than in RA control patients. Treatment was similar in all patient groups. No direct association was seen between LGL numbers and duration of RA or neutrophil counts in RA groups.

CONCLUSION

Hematologic abnormalities in FS extend beyond neutropenia. Although similarities were seen between FS patients and FS patients with the LGL syndrome (e.g., CD4 lymphopenia), evidence for a gradation from FS to the LGL syndrome was not seen, thus favoring the hypothesis that a "transforming event" is required.

Liver disease in twins with Felty's syndrome

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Primary T cell lymphoma of the liver in a patient with Felty's syndrome

We describe a case of primary T cell lymphoma of the liver developing in a patient with Felty's syndrome (FS). We discuss the possible relationship of the two conditions with particular reference to liver disease in FS, and the role of the T cell in RA.

Sequential administration of cyclophosphamide and granulocyte-colony stimulating factor relieves impaired myeloid maturation in Felty's syndrome

A patient with Felty's syndrome (FS) and persistent profound neutropenia developed recurrent infections and sepsis syndrome. No impairment of granulocyte-macrophage colony development was observed in vitro. Marrow morphology revealed an absence of mature neutrophil forms despite administration of granulocyte-colony stimulating factor (G-CSF). However, pretreatment with bolus cyclophosphamide (CY) permitted the growth factor to relieve this impairment of late myeloid maturation and resulted in a brisk, albeit short, burst of neutrophilia. This suggests that immune interference in myelopoiesis can be overcome by growth factor administration if immune activity is adequately dampened by immunosuppressive therapy.

Analysis of lymphocyte phenotype and T cell receptor genotype in Felty's syndrome

Natural killer (NK) cells and CD3+ large granular lymphocytes (LGL) were investigated in patients with Felty's syndrome (FS), rheumatoid arthritis (RA) and healthy controls. In most patients with FS, NK cell number and activity were decreased. CD3+ LGL were unchanged. However, in one patient a marked expansion of CD3- CD16+ CD56+ (NK) cells was seen and in a second, an expansion of CD3+ LGL. In FS there was also an increase in HLA- DR+ and CD8+ but not gamma delta+ T cells. Three of 11 patients with FS studied demonstrated a dominant rearrangement of the T cell receptor beta gene constant region consistent with oligoclonal T cell expansion.

The pathogenesis of nodular regenerative hyperplasia of the liver associated with rheumatoid vasculitis

Nodular regenerative hyperplasia (NRH) is an uncommon liver disease that typically develops in the setting of a chronic illness such as Felty's syndrome. Although the pathogenesis of NRH has not been defined, vasculitis has been postulated to play an important pathogenetic role in some cases of NRH, even though the association of NRH and vasculitis has been reported rarely. We describe two unusual cases of NRH in patients with Felty's syndrome complicated by rheumatoid vasculitis. Morphometric analysis demonstrated evidence of injury to the hepatic vasculature in the form of loss of small intrahepatic arteries and portal spaces, findings that support the hypothesis that hepatic arteritis plays a role in the development of NRH in cases associated with systemic vasculitis.

Coexistent Felty's syndrome and palindromic rheumatism

Palindromic rheumatism is a syndrome of intermittent abrupt onset monoarthritis with asymptomatic intercritical periods of variable duration, which commonly evolves into rheumatoid arthritis. Felty's syndrome consists of leucopenia (selective neutropenia) and splenomegaly, usually occurring in longstanding classic rheumatoid arthritis. Felty's syndrome can be confused with the more recently recognised rheumatoid arthritis associated large granular lymphocyte proliferative disease. This paper describes a patient with palindromic rheumatism presenting with Felty's syndrome in whom large granular lymphocyte proliferative disease was ruled out by lymphocyte phenotyping.

The clinical course of Felty's syndrome compared to matched controls

In a cohort of 919 patients with definite or classic rheumatoid arthritis followed prospectively since 1966, we identified 36 patients with Felty's syndrome (FS). Their clinical course was compared to that of 72 matched controls from the same cohort. Patients with FS had more extraarticular features and more infections than control patients. The presence of joint erosions, serial Lansbury indices, and death rates were similar in both groups. Cardiovascular disease was the commonest cause of death in both groups, accounting for 32% of all deaths. Sepsis accounted for 10% of deaths in the group with FS and 13% of deaths in the controls.

The Felty syndrome: a case-matched study of clinical manifestations and outcome, serologic features, and immunogenetic associations

Thirty-two patients with the Felty syndrome, defined by the presence of rheumatoid arthritis, splenomegaly, and neutropenia, have been studied in comparison with 32 patients with rheumatoid arthritis matched for age, sex, and disease duration, and 9 patients with rheumatoid arthritis and idiopathic neutropenia. Patients with the Felty syndrome had severe destructive arthritis, which progressed during follow-up despite little evidence of objective synovitis, and a higher frequency of extra-articular manifestations, including vasculitis. Bacterial infection tended to occur in patients with the lowest neutrophil count but continued to occur in some despite normalization of the WBC. Prognosis was poor and 8 deaths occurred, predominantly from sepsis. Serologic features were prominent. High titers of IgG rheumatoid factor and circulating immune complexes characterized patients with persistent neutropenia. A family history of rheumatoid arthritis was more common in patients with the Felty syndrome. The association with HLA DR4 was very strong; in addition there was an increased frequency of the DQw3 variant, 3b, suggesting that HLA Class II genes in linkage with DR4 may contribute to disease expression.

Phenotypic and genotypic analysis of mononuclear cells from patients with Felty's syndrome

Phenotypic and genotypic characteristics of the peripheral blood mononuclear cells in nine patients with Felty's syndrome have been examined. One patient had an increased number and percentage of peripheral blood mononuclear cells with the phenotype CD3+ Leu-7+ CD16+ and showed a clonal rearrangement of the T cell receptor B chain gene. The remaining eight patients all showed a germline configuration of the T cell receptor B chain gene. In two patients an increased proportion of CD3+ Leu-7+ CD16- peripheral blood mononuclear cells (45 (SD 11)% of peripheral blood mononuclear cells) were found, while the remaining six patients had proportions of CD3+ Leu-7+ cells similar to those of patients with uncomplicated rheumatoid arthritis. These data confirm that patients with Felty's syndrome are heterogeneous, with at least three different peripheral blood mononuclear cell phenotypic subsets. One subset is characterised by a clonal expansion of an unusual lymphocyte subpopulation, another by polyclonal expansion, and the third subset has the same proportions of peripheral blood mononuclear cells as patients with uncomplicated rheumatoid arthritis.

Sinusoidal lymphocytosis of the liver in Felty's syndrome with a review of the liver involvement in Felty's syndrome

A 68-year-old woman with Felty's syndrome had massive hepatomegaly. Liver biopsy showed diffuse infiltration of the sinusoids with mature lymphocytes (sinusoidal lymphocytosis of the liver). Nodular regenerative hyperplasia of the liver and portal fibrosis were not found. Although liver involvement is frequent in association with Felty's syndrome, sinusoidal lymphocytosis of the liver is unusual.

The spleen in Felty's syndrome: a histological, morphometrical, and immunohistochemical study

A histological study employing morphometrical and immunohistochemical methods was performed in 3 spleens removed because of Felty's syndrome (FS). A comparison was made with control spleens and with spleens removed from patients with idiopathic thrombocytopenic purpura (ITP) or autoimmune hemolytic anemia (AIHA). In FS, the spleen is enlarged, mainly due to expansion of the red pulp. The sinuses are enlarged, too, and contain many macrophages. 2 of our specimens showed many hyperplastic germinal centers; the 3rd contained no germinal centers. Only in the former cases did splenectomy lead to an increase in the number of circulating granulocytes. Immunohistologically, FS spleens differed from the control, the ITP, and the AIHA spleens. The results have provided further evidence indicating that the pathogenesis of granulocytopenia in FS differs from that of autoimmune hematocytopenias, and have given rise to the hypothesis that, in FS, the spleen is the site of interaction between immune complexes and granulocytes.

Clonal proliferation of large granular lymphocytes in rheumatoid arthritis

Some patients with chronically elevated large granular lymphocyte (LGL) numbers have rheumatoid arthritis (RA). Since these patients also may have neutropenia and splenomegaly, their symptoms resemble those of patients diagnosed as having Felty's syndrome (FS). We studied the immunophenotypic and genotypic characteristics of mononuclear cells from patients with RA and neutropenia to better determine the extent of heterogeneity in this condition. Four patients had markedly increased numbers of LGLs, which expressed HNK-1 antigen and IgG Fc receptors. In contrast, the remaining 8 patients, who had FS, had normal LGL counts, and surface marker studies showed normal numbers of HNK-1 and IgG Fc receptor positive cells. Clonal rearrangement of the T cell receptor beta chain gene was demonstrated in all 4 patients with excess LGLs, whereas a germline configuration of this gene was present in all 6 FS patients in whom this was studied. These results suggest that there are diverse groups among patients with RA and neutropenia. Since prognosis may differ, it is important to recognize that some patients who are considered to have Felty's syndrome may have a clonal proliferation of LGLs.

High dose intravenous gamma globulin for Felty's syndrome

High dose intravenous gamma globulin (IV-IgG) was given to 5 patients with Felty's syndrome. The neutrophil count did not change with IV-IgG therapy and no side effects were encountered. We conclude that neutropenia in Felty's syndrome is not comparable to autoimmune hemocytopenia with respect to the response to IV-IgG.

[Biological screening of immuno-mediated marrow insufficiency by means of the CFU-GM assay]

We studied in agar growth behaviour of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) in 16 patients with marrow failure in order to discriminate patients with cells inhibiting granulopoiesis both in bone marrow and peripheral blood. Our experimental design was based on: a) agar culture of bone marrow cells before and after treatment with antilymphocyte globulin (AGL); b) agar co-culture of marrow cells with autologous lymphocytes from peripheral blood. ALG treatment of marrow cells determined CFU-GM growth increase in 4 out of 10 patients; in the same patients co-culture with autologous lymphocytes showed a significant inhibition of CFU-GM growth. The growth enhancement induced by ALG treatment "in vitro" associated with growth inhibition in the coculture suggests the existence of a lymphocyte population suppressing the granulopoiesis both in bone marrow and peripheral blood. With this work we propose an experimental model in order to discriminate marrow failure based on cell-mediated suppression of CFU-GM growth in patient susceptible of immunosuppressive therapy with ALG.

Felty's syndrome presenting without arthritis

A patient with splenomegaly, severe granulocytopenia and a strongly positive rheumatoid factor test initially had no clinical evidence of rheumatoid arthritis. Leukopenia responded to splenectomy and did not recur during one year of follow up. Symmetrical metacarpophalangeal joint swelling developed after nine months. This case emphasizes that arthritis may occasionally be a late and minor manifestation of Felty's syndrome.

Pasteurella multocida septicaemia complicating Felty's syndrome: A case report

A patient with Felty's syndrome complicated by septicaemia due to Pasteurella multocida is presented. Disease caused by this organism is unusual in humans and its occurrence in the absence of trauma, as was the case in our patient, even more so.

Portal hypertension in Felty's syndrome

Idiopathic portal hypertension, usually with esophageal varices, minimal but definitely abnormal liver tests and subtle or no changes on percutaneous liver biopsy has been reported in only a few patients. A case associated with Felty's syndrome in a 65-year old woman with a 44-year history of rheumatoid arthritis is reported in which the liver tests and liver biopsy were normal. Portal hypertension, varices and a patent portal venous system were documented. No surgical procedure was undertaken and she has done well in the 18 months since these studies were performed. A conservative approach is probably warranted in such cases.

Felty's syndrome

An unusual case is presented in which a patient complained of oral ulceration and soreness of the mouth and throat. The results of clinical and laboratory investigations are reported and it was concluded that these oral symptoms were associated with Felty's Syndrome. After treatment of oral infection and a dental clearance the patient was virtually symptom-free for five months. The patient had a relapse and was admitted to hospital for treatment of overwhelming infection. Splenectomy was performed without sustained benefit and the patient died six weeks later.

Splenectomy for Felty's syndrome. Clinicopathological study of 27 patients

The major clinical and pathological features and the long-term follow-up of 27 patients with Felty's syndrome who were treated with splenectomy for sever granulocytpenia and for acute, chronic, or recurrent infection were studied. Granulocyte counts rose within days in most patients, although slow responses and transient granulocytopenia did occur; only 12% of the patients had persistent or recurrent granulocytopenia. Infections resolved promptly in 77% of the patients, more slowly in the remainder, and only one patient had new problems of infection after aplenectomy. Splenic enlargement, present in all but one case, was attributable to expansion of the sinusoidal pulp. The most substantial pathological features of immune stimulation included germinal center hyperplasia and prominent clusters of plasma and preplasma cells within sinuses.

Noncirrhotic portal hypertension in Felty's syndrome

A case of Felty's syndrome with nodular regenerative hyperplasia of the liver, presinusoidal portal hypertension, and bleeding esophageal varices is reported. Increased splenic blood flow may be a contributing factor to the development of the regenerative nodules. The portal hypertension is postulated to be a result of intrahepatic vascular compression.

Nodular, non-cirrhotic liver associated with portal hypertension in a patient with rheumatoid arthritis

A patient with rheumatoid arthritis developed portal hypertension and died from bleeding oesophageal varices. The liver was small and showed a nodular, non-cirrhotic pattern similar to that described by Blendis et al (1970 and 1974) in association with Felty's syndrome. This appears to be the first report of a patient with this liver lesion associated with rheumatoid arthritis in the absence of Felty's syndrome. The liver lesions described here are compared with partial nodular transformation and nodular regenerative hyperplasia; in spite of some differences it is not proven that these are distinct entities and further study is required to settle this question.