Primary pulmonary lymphoma

Bronchial mucosa-associated lymphoid tissue

MALT is a lymphoid tissue specialising in mucosal defence 1. It was first described in the gastrointestinal tract of animal models, then in the human ileum. It comprises of Peyer's patches, a lamina propria, intra-epithelial lymphocytes and mesenteric lymph nodes. Peyer's patches are lymphoid nodules with an architecture similar to that of lymph node follicles, except that the marginal B zone is more highly developed in the former. The lamina propria contains immunoglobulin (Ig) A-secreting plasmocytes and T lymphocytes. Phenotypically, intra-epithelial lymphocytes are CD8+ T-cells. The stomach is the most frequent site of MALT lymphoma and serves as a model for pulmonary MALT lymphoma. As in the stomach, MALT is absent from the lung in physiological circumstances. During chronic antigenic stimulation (by Helicobacter pylori, for example), MALT can develop in the stomach and undergo secondary lymphomatous transformation arising from marginal zone B-cells. In order to develop, the malignant B-cell clone requires the presence of T-cells specifically directed against H. pylori antigens. Thus, H. pylori eradication can lead to lengthy complete remission of gastric lymphoma 23. No triggering antigens have so far been identified in the lung, but chronic antigenic stimulation in certain autoimmune disorders (systemic lupus erythematosus, multiple sclerosis, Hashimoto's thyroiditis and particularly Gougerot-Sjögren's syndrome) are considered to affect the onset of pulmonary MALT lymphoma 23.

Epidemiology

Low-grade NHL-B accounts for 58–87% of cases of PPL in pathological series 5, 12, 15, 17. Nearly 90% of these cases correspond to MALT-type NHL 12, 15, 17. Age of onset is ∼50–60 yrs (12–79 yrs) and subjects <30 yrs are rarely affected [5, 9, 11, 13, 14, 16, 24]. The two sexes are equally affected [5, 9, 11, 13, 14, 16, 24].

Clinical and radiological signs

Nearly half these patients are asymptomatic at diagnosis and are identified fortuitously on the basis of a radiological pulmonary anomaly [5, 11, 13, 14, 24]. When present, symptoms, such as cough, mild dyspnoea, chest pain and occasionally haemoptysis, are nonspecific [5, 9, 11, 13, 14, 16, 24]. Pulmonary auscultation reveals crackles in <20% of cases 24. By definition, extra-pulmonary manifestations are restricted to general signs (fever and weight loss) and occur in less than one quarter of patients [5, 11, 13, 14, 24]. The usual radiological aspect (50–90% of cases) is a localised alveolar opacity, with a diameter of <5 cm and blurred or well-defined contours (according to the series); it is associated in nearly 50% of cases with an air bronchogram (fig. 1a⇓) [13, 14, 24]. Computed tomography (CT) (figs. 1b and c⇓), which is more sensitive than standard radiography, has demonstrated that the lesions are usually bilateral (60–70%) and multiple (70–77%) 25, 26. Nearly all these lesions contain clear areas corresponding to an intact bronchial lumen (fig. 2⇓). The presence of distended bronchi within the lesions is a good diagnostic sign, although the underlying mechanism is unexplained 26. Less than 10% of patients have bilateral diffuse reticulonodular opacities, atelectasia or pleural effusion [13, 14, 24]. CT can reveal hilar and mediastinal adenopathies 9, 24. The interval between the first clinical or radiological manifestations and diagnosis ranges from 5 months to 8 yrs [5, 11, 13, 14, 24].

Contribution of bronchial endoscopy

Bronchial endoscopy usually shows a normal macroscopic aspect 24, although abnormalities ranging from mucosal inflammation to bronchial stenosis can be observed 24. The diagnostic yield of bronchial, and especially transbronchial, biopsy is higher when it targets visible endobronchial lesions or radiographic abnormalities 24. However, the absence of specific signs in most of these samples necessitates further diagnostic investigations [5, 9, 11, 13, 14, 16, 24]. Bronchoalveolar lavage (BAL) is very useful for differential diagnosis of chronic alveolar opacities 27. In contrast, its value for the positive diagnosis of PPL is inadequately assessed. BAL has proven useful in isolated cases of PPL 28–, while its use is not always mentioned in large published series [5, 9, 11, 13, 14, 16]. BAL appears to be particularly valuable if it shows lymphocytic alveolitis (lymphocytes >20% of total cells), which is found in about two-thirds of these patients 24, 27, 29, 31. This lymphocytosis, which is usually composed principally of T-cells, is only a specific sign when >10% of B lymphocytes are present 24, 29, 32. B-cell alveolitis is particularly valuable when its clonal nature can be demonstrated by the detection of Ig gene clonal rearrangements using molecular biology-based methods (Southern blot or reverse transcriptase-polymerase chain reaction) 35–, 39, 40. However, these methods are not widely used in routine practice and require further evaluation of their sensitivity and specificity. They can already be used to diagnose a recurrence of histologically proven PPL. Screening for monoclonal Ig in the BAL supernatant by immunoelectrophoresis 24, 33, 38, 41 and restricted membranous or intracytoplasmic Ig light-chain expression by slide immunohistochemistry or flow cytometry 29–, 38 have been used but have been replaced by molecular biology-based methods.

Diagnostic criteria

The diagnosis of MALT-type NHL is based on histological examination of surgical samples or bronchial, transbronchial or transthoracic biopsy material.

Differential diagnosis

Differential diagnosis of MALT-type PPL is based on clinical and histological grounds. Clinically, the problem boils down to diagnosing MALT-type PPL after radiological identification of a chronic localised or diffuse alveolar or interstitial opacity, which can have a wide range of aetiologies (table 1⇓).

Histologically, especially when the sample is small, the main difficulty is distinguishing MALT-type NHL from diffuse lymphoid hyperplasia or interstitial lymphoid pneumonia (ILP), and follicular bronchitis (FB). This distinction may seem irrelevant to the clinician, because the radiological and clinical features of these disorders often differ from those of MALT-type PPL 47. Other histological entities, such as extrinsic allergic alveolitis, can be considered, owing to their similar radiological expression and the presence of a lymphoid lesion. Some other nodular pulmonary lesions also have a lymphoid contingent, such as plasmocyte granuloma, inflammatory pseudotumours, fibrous histiocytoma, pulmonary hyalinising granuloma, intrapulmonary adenopathies, and Castleman's disease 48.

Pretreatment extension work-up

Nodal lymphoma is ruled out by abdominal and thoracic CT with contrast enhancement. Although bone marrow involvement is far more frequent in lymphoma of the nodal or splenic marginal zone 21, bone marrow biopsy is crucial, showing signs of invasion in ≤20–30% of patients in recent series of MALT lymphoma [49, 50]. Similarly, these series showed concomitant involvement of other mucosal lymphoid sites in 25–35% of cases 47–, and even more frequently in patients with MALT lymphoma not involving the gastrointestinal tract. The search for other mucosal sites must include ophthalmological and ear, nose and throat (ENT) examinations (with magnetic resonance imaging (MRI) or CT of the salivary and lacrimal glands in suspect cases), plus upper gastrointestinal endoscopy (and coloscopy plus small-intestinal transit, according to some authors). The only useful laboratory tests in the pretreatment work-up are serum electrophoresis and immunoelectrophoresis. Monoclonal gammopathy (IgM in eight out of 10 cases) is found in 20–60% of cases, especially in forms with plasmocyte differentiation 5, 9, 14, 24. A recent study showed that an elevated β2 microglobulin level is an independent predictor of poor survival 50.

Course, prognosis and treatment

Low-grade B-cell primary pulmonary lymphoma

In <10% of cases, low-grade PPL-B does not meet the histological criteria of MALT-type NHL. According to the WHO classification 18, these cases can correspond to follicular or mantel lymphocytic NHL or CLL. The clinical and pulmonary radiological aspects are similar to those of MALT-type PPL 12, 15.

High-grade primary pulmonary lymphoma-B

High-grade NHL-B represents 11–19% of cases of PPL in published series 12, 15, 17; MALT-type NHL coexists in ∼50% of cases. High-grade NHL-B often occurs in patients with underlying disorders, such as solid organ (heart/lung) transplantation with cyclosporine A or OKT3 immunosuppression 56–, human immunodeficiency virus (HIV) infection 60– and Gougerot-Sjögren's syndrome 64. It is reminiscent of high-grade pleural NHL in acquired immune deficiency syndrome (AIDS) patients 60, 65 and in patients with pleural sequelae of collapsotherapy. Epstein-Barr virus (EBV) has been implicated in the onset of some of these high-grade NHL affecting the lung 62, 63, 65–.

Excluding HIV-infected subjects, mean age at onset is ∼60 yrs (30–80 yrs) 5, 9, 10, 15, 24. Patients are usually symptomatic, with respiratory manifestations, fever or weight loss 5, 9, 10, 15, 24. Radiological investigations usually show a single pulmonary mass or atelectasia. Pleural effusion is also often present 5, 9, 10, 15, 24. In the current authors' experience, multiple and/or excavated opacities are frequently found in HIV-infected patients 61–. Bronchial endoscopy is often abnormal, with budding or infiltrative stenosis with a tumoural aspect 5, 9, 24. The histological diagnosis is generally easy, even with very small samples (bronchial, transbronchial or transthoracic biopsy), owing to the presence of blast-like lymphoid cells with strong mitotic activity, clearly indicative of malignancy 5, 9, 24, 69. The lymphoid infiltrate aggresses the bronchial, vascular (endoluminal invasion) or pleural structures, and necrosis is usually found. Most cases are immunoblastic and centroblastic NHL 5, 9, 12, 15, 17, 24. Histology has a limited role in differential diagnosis 48. The highly atypical cytological aspect means that immunohistochemistry is required to rule out carcinoma, melanoma or sarcoma if there is a marked fibroblastic reaction, and especially extension of a nodal lymphoma or leukemic involvement. Markedly angiotropic lesions raise the possibility of lymphomatoid granulomatosis.

Survival is poorer in high-grade PPL than in low-grade PPL. Overall, the median survival time is ∼8–10 yrs 5, 9, 24, but it is far lower in patients with underlying disorders (HIV infection, transplantation, collapsotherapy). Progression and local or distant relapse occur earlier and are more frequently 5, 9, 24. Treatment after surgical resection is often based on the combination chemotherapy regimens used for high-grade nodal NHL 5, 9, 24.

Primary pulmonary plasmocytoma

Primary pulmonary plasmocytoma is extremely rare. Less than 50 cases have been reported in the literature 70, 71. Age at onset is ∼40 yrs, although cases have been described in children and older patients 70, 71. The two sexes are equally affected. Patients are usually asymptomatic, but fever, weight loss, chest pain, dyspnoea, cough and even haemoptysis have occasionally been described 70, 71. The most common radiological aspect is that of an isolated pulmonary nodule, but a case of bilateral diffuse lung disease has been reported 72. A hilar adenopathy is observed in <10% of cases 70. Bronchial endoscopy is always normal and the diagnosis is almost always based on thoracotomy findings 70. Histologically, the lesions are composed solely of plasmocytes with variable degrees of cytological anomalies 70, 71. Amyloid lesions can be present 73. By definition, immunohistochemical studies show monoclonal intracytoplasmic immunoglobulin expression 70, 71, 73. This differentiates these cases from low-grade lymphoma, which always contains small lymphocytes and reactive plasmocytes expressing polyclonal Ig 70, 71, 73.

In patients with suspected primary pulmonary plasmocytoma, myeloma must be ruled out by normal bone marrow and skeletal examination 70. Treatment is mainly based on surgical excision of the plasmocytoma. If surgery is contraindicated, most plasmocytomas are radiosensitive. The overall 2- and 5-yr survivals of primary pulmonary plasmocytoma are 66% and 40%, respectively 71. Despite complete tumour excision, 15–30% of patients develop multiple myeloma within a few years 70.

Pulmonary intravascular lymphoma

Pulmonary intravascular lymphoma is due to proliferation of atypical lymphoid cells within the lumen of capillaries, arterioles, venules and lymph ducts, with little or no invasion of the adjacent parenchyma. It is usually located in the central nervous system and skin. The underlying mechanism appears to be the loss of certain surface receptors on lymphoid cells, preventing their extravascular migration. Pulmonary involvement is rare 74, 75, with about 15 cases reported in the literature. Usually, the clinical and radiological picture is that of diffuse interstitial lung disease with hypoxemia and fever 75, 76. There is no mediastinal node involvement. There is frequently an altered general state and a lactate dehydrogenase elevation 77, and cerebral, renal or cutaneous involvement is almost always present 74, 75. A case of pulmonary arterial hypertension 76 and a case of respiratory insufficiency with air trapping 77 have been reported. Transbronchial biopsies can assist with the diagnosis 77, as can cytological analysis of pulmonary capillary blood cells 78. Combination chemotherapy regimens used in high-grade NHL have some efficacy, giving a complete response rate of ∼50%.

Is lymphomatoid granulomatosis a lymphoid malignancy?

Clinically, LG is characterised by the absence of node, hepatosplenic or bone marrow involvement evocative of NHL. Its natural course is extremely variable. Spontaneous remissions have been reported 34, 81, 82 and prolonged complete remissions have been obtained in nearly 50% of patients with steroids and cyclophosphamide 83, 84. However, in most published series the prognosis is grim, with death occurring in >50% of cases, despite combination chemotherapy 34, 79, 81, 84, 85. Histologically, the lesions sometimes have a lymphomatous aspect, with areas of large atypical lymphoid cells. Authentic high-grade NHL is diagnosed during the course of the disease or at autopsy in from 10% to nearly 50% of patients. Immunohistochemical and molecular biology-based analyses performed in two series showed evidence of clonality in five out of 11 and six out of nine cases of LG 86, 87. Given this variable clinical course and lesional aspect, some authors grade the lesions from 1 (minimal anomalies) to 3 (maximal anomalies), based on the proportions of atypical and inflammatory cells 81, 85, 88, 89. A recent study showed a correlation between lesional grade and the B-cell proliferation index, but not the T-cell, macrophage or natural killer-cell proliferation index. The proliferation index of grade-3 lesions appears to be identical to that of large B-cell NHL 90.

Is lymphomatoid granulomatosis a lymphoid lesion of the T or B phenotype?

The definition of LG as an immunoproliferative T-cell disorder is now being challenged. The T-lymphomatous nature of some cases of LG had been suggested on the basis of an aberrant T-cell phenotype or a chromosomal abnormality, but clonal rearrangement of T-cell receptor genes has never been demonstrated 83, 87, 91–. Other studies based on immunohistochemistry and molecular biology showed, in fact, that most LG correspond to the definition of B-cell NHL. In these studies, the large atypical cells expressed B-cell markers (CD20) and showed restricted Ig light-chain expression (K or L) 87, 91, 92, 95, 96. Molecular biology studies usually show clonal rearrangement of Ig genes 86, 87, 91, 96.

Is lymphomatoid granulomatosis induced by Epstein-Barr virus?

A large number of studies point to a role of EBV in the pathogenesis of LG, as in post-transplant and HIV-related lymphoproliferative syndromes 86, 87, 97, 98. Viral proteins (lysosome-associated membrane protein (LMP) and EBV-associated nuclear antigen (EBNA)) or viral genomic sequences (EBR1 and EBR2) have been found within the lymphoid infiltrate in 59–72% of cases of LG studied so far 86, 87, 97, 98. A recent study showed that EBV-infected tumour cells bear B-cell markers 98. Viral proteins (LMP1 and EBNA2) normally induce a cytotoxic T-cell response, which appears to be deficient in LG 98.

Epidemiology

LG is rare. Between 500–600 cases have been reported in the literature, in the form of case reports and series of 10–150 patients 34, 79, 82, 84, 85, 88, 99–. Age at onset is ∼30–50 yrs (2.5–85 yrs) 34, 79, 80, 84, 85, 88, 99–. Males seem to be more susceptible than females, with a sex ratio of between 1–6.5 males per female 34, 79, 82, 84, 85, 88, 99–. No geographical or ethnic susceptibility factors have been found.

Clinical and radiological pulmonary signs

Nearly 90% of patients are symptomatic at diagnosis and present with a 4- to 8-month history of general and respiratory symptoms 34, 79, 82, 84, 85, 88, 99–. Respiratory symptoms are found in 54% to >80% of cases, and mainly consist of cough and dyspnoea. Chest pain and potentially life-threatening haemoptysis can occur 79, 82, 99. Fever, weight loss or sweating occur in 30–70% of cases. Cases of acute respiratory distress have been reported. In one series, the average oxygen tension in arterial blood was 8.9 kPa (67 mmHg (40–100 mmHg)) and there was a restrictive, obstructive or mixed syndrome in 40%, 20% and 15% of cases, respectively 34.

The radiological aspect in >80% of cases is that of multiple poorly-defined nodular opacities measuring 1–8 cm in diameter. They are bilateral and predominate in the lower lobes 34, 79, 81, 82, 84, 85, 88, 99, 102–. The nodules have a peribronchovascular distribution and tend to converge to form pseudotumoural masses and excavate, and can disappear or migrate spontaneously (“wax and wane”) 82, 88, 103 (fig. 4⇓). Anatomical-radiological correlation studies have shown that excavated masses correspond to infarcted granulomatosis lesions 104, 105. Unilateral or single nodules, alveolar opacities, and bilateral reticulonodular involvement are more unusual. Mild pleurisy is observed in 40% of cases 34, 79, 82, 85, 99, 102, 106 and pneumothorax has only been described in patients with excavated nodules 82. Hilar adenopathies are found in 25% of cases 81, 82, 102.

Extrapulmonary manifestations

Extrapulmonary manifestations mainly affect the skin, nervous system or ENT sphere. They can precede, coincide with or follow the onset of respiratory manifestations 34, 79, 81, 82, 84, 85, 88, 99. Cutaneous involvement is observed in 36–53% of cases, and consists of erythema, nodules and, more rarely, mucosal ulceration 85. Neurological involvement takes the form of central deficits (blindness, hemiparesis, ataxia, convulsions, coma, headache, confusions, etc.), sensory-motor neuropathies affecting the limbs or cranial nerves, and, far more rarely, hypothalamic-pituitary involvement, and occurs in 10–35% of cases 34, 79, 81, 82, 84, 85, 88, 99. Ulceration of the upper airways is described in 10–30% of cases 34, 81, 84, 85. The frequency of renal involvement is variously reported; it is ∼0–10% at diagnosis and increases during the course of the disease, reaching 30–40% in some autopsy series 79, 81, 84. It is almost always due to a mass syndrome; creatinemia and the urinary sediment are usually normal. Specific peripheral adenopathies are also infrequent, being observed in 5–8% of cases 34, 79, 81, 84. Other extrapulmonary manifestations, such as arthralgia and ocular or gastrointestinal involvement, were observed in ∼10% of cases in some series 34, 79, 81, 84. There have been anecdotal reports of involvement of numerous other organs 34, 79, 81, 84, 85, including muscle, thyroid, liver, spleen, testicle, bone marrow, adrenal glands, heart, prostate, ovaries, etc.

Diagnostic criteria

The diagnosis of LG is based on histological examination of surgical pulmonary samples. Endoscopic samples are rarely positive 34. Other histological samples of adequate size can sometimes be obtained by biopsy of skin lesions (positive in 44% of cases) or ENT tissues (86%) 34. It is recommended to biopsy all accessible sites, owing to the variable proportions of atypical cells found at a given time in the different lesions.

Differential diagnosis

Clinically, the main difficulty is in diagnosing LG in patients with multiple excavated nodular opacities and subacute general and respiratory signs (table 2⇓). An infectious cause must be ruled out in localised forms, by histochemical staining (Ziehl, Grocott, Gram). Some aetiologies are more difficult to identify, owing to radiological-clinical and/or histological features resembling those of LG. These aetiologies include Wegener's granulomatosis, necrotising sarcoidosis, and benign granulomatous and lymphocytic angiitis 6, 34, 79, 80, 85, 88, 108. Other histological entities can also be discussed, owing to their clinical expression and the possibility of lymphoid lesions. Given the therapeutic implications, it is essential to rule out Hodgkin's disease and high-grade angiotropic NHL before diagnosing LG.

Pretreatment extension work-up

The extension work-up comprises a search for cutaneous and especially neurological involvement, by cerebral MRI. Owing to their relative frequency, renal and ENT lesions should also be sought. Finally, node and bone marrow involvement must be searched for, as it makes the diagnosis of LG/diffuse NHL highly probable 81.

No particular laboratory test is required for diagnosis or prognostication in this setting. Anaemia, a biological inflammatory syndrome, hyperleukocytosis or, on the contrary, leucopenia or lymphopenia are often present 34, 81, 82, 84, 85, 88. The immunological work-up shows only nonspecific abnormalities 85, 88. Antinuclear antibodies and rheumatoid factor are very rarely positive 81, 82. Hypogammaglobulinaemia or hypergammaglobulinaemia with circulating immune complexes have been described 34, 81, 82. Cutaneous anergy to recall antigens or dinitrochlorobenze is observed in >50% of cases 84, 88. Lymphocyte proliferation to antigens or mitogens is also subnormal.

Course, prognosis and treatment