Tracheobronchial amyloidosis: evidence for local B-cell clonal expansion

To the Editors:

Amyloidosis is characterised by the deposition of insoluble protein fibrils in organs and tissues, which leads to organ dysfunction. Amyloidosis is classified according to the composition and localisation of fibrils. The most frequent amyloidosis is immunoglobulin (Ig)-light-chain (AL) amyloidosis. In systemic AL amyloidosis, the fibrils are derived from circulating monoclonal light chains that are usually produced by intramedullary clonal plasma cells. Localised AL amyloidosis is most often identified in upper respiratory, urogenital and gastrointestinal tracts, in the skin and in the orbit. In such circumstances, the amyloidogenic light chains are produced by a subtle clone of lymphoplasma cells localised near the amyloid deposits [1]. Characterising the associated clonal cells is often not possible because of their low number.

Tracheobronchial amyloidosis is a rare form of localised amyloidosis [1,2]. To our knowledge, local B-cell clonal expansion has never been consistently demonstrated in tracheobronchial amyloidosis. We present the first case of tracheobronchial amyloidosis with molecular demonstration of localised tracheobronchial B-cell clonal proliferation and the results of targeted B-cell therapy with rituximab.

A 41-yr-old female complained of persistent cough and expectoration for 1 yr. She was a 10-pack-yr active smoker. The physical examination was unremarkable. Lung function tests revealed an obstructive pattern, with a forced expiratory volume in 1 s of 1,880 mL (66%) and vital capacity of 3,420 mL (102%) without reversibility. Thorax computed tomography (CT) revealed a thickening of the trachea and primary bronchi without sparing the posterior tracheal wall (fig. 1a). Bronchoscopy confirmed a diffuse infiltration of the mucosa from the beginning of the trachea to the beginning of the tertiary bronchi, without sparing the posterior wall (fig. 1b). A search for pathogens gave negative results. Tracheal biopsies showed abundant submucosal deposits of an amorphous, mildly eosinophilic material without detectable lymphoproliferation (fig. 1c). The material was stained with Congo red (fig. 1d) and produced green birefringence under polarised light. Immunofluorescence of frozen biopsies was positive for lambda light chain antibody (fig. 1d, insert) but not kappa, IgA or IgM.

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Figure 1–

a) Chest computed tomography scan showing wall thickening of the trachea in a 41-yr-old female with persistent cough and expectoration. b) Endoscopic view of the carina showing wall thickening of the trachea and carina. c) Haematoxylin and eosin staining of bronchial biopsies showing abundant submucosal deposits of an amorphous, mildly eosinophilic material. d) Congo red staining of bronchial biopsies confirmed amyloidosis that was positive for lambda light chain on immunofluorescence staining of frozen biopsies (insert).

B-cell clonality analysis of the bronchial biopsy was performed by PCR according to the European BIOMED-2 technique [3]. Briefly, the diversity of heavy chain CDR3 lengths was analysed with 100 ng DNA for each FR1-JH and FR2-JH PCR. The amplified products were run on an ABI Prism 3100 Genetic analyser (Applied Biosystems, Foster City, CA, USA). Results were analysed by use of Genscan (Applied Biosystems). A dominant B-cell clone was documented in one of the two tested fragments. B-cell clonality analysis could not be interpreted from the bone marrow.

Routine biological tests, including serum protein electrophoresis, gave normal results. Serum and urine immunoelectrophoresis did not reveal monoclonal Ig. Peripheral blood lymphocyte phenotyping was normal and B-cell repertoire was polyclonal. Bone marrow, labial salivary gland, rectum and abdominal fat-pad biopsies did not reveal amyloidosis or lymphoproliferation. Echocardiography results were normal. A diagnosis of tracheobronchial amyloidosis, AL type, was given.

Because the pulmonary obstruction was not severe, local endobronchial treatment was not necessary. After discussion and informed consent by the patient, treatment with rituximab was agreed. Rituximab was administered in February 2009 as an intravenous infusion of 375 mg·m⁻²·week⁻¹ for 4 weeks, with maintenance therapy after 1 yr (375 mg·m⁻² in February 2010 and every 3 months until November 2010). Inhaled corticosteroids and bronchodilators were given. Rituximab was well tolerated. The cough was ameliorated, and the patient presented only one exacerbation with worsening of cough and expectoration requiring oral antibiotics. CT, pulmonary function tests and bronchoscopy evaluation at 12 and 24 months after rituximab infusion showed stable disease. Repeated analysis of tracheal biopsies revealed a persistent B-cell clone after 12 months.

Our report is the first molecular demonstration of the presence of a local B-cell clone in tracheobronchial amyloidosis and the first evaluation of the efficacy of B-cell-targeted therapy with rituximab, an anti-CD20 monoclonal antibody, for the disease.

Tracheobronchial amyloidosis is an uncommon diagnosis [1]. The disorder has been associated with tracheobronchopathia osteoplastica, which is characterised by calcified or cartilaginous submucosal nodules within the airways [4]. Tracheobronchial amyloidosis typically presents after the fifth decade of life, with dyspnoea, cough and, occasionally, haemoptysis. Narrowing of the airways can cause distal atelectasis or recurrent pneumonia. Symptomatic tracheobronchial amyloidosis is usually localised. However, its course is not necessarily benign: three out of seven patients followed by Hui et al. [5] died of respiratory failure or secondary pneumonia, three out of four patients followed at the Mayo Clinic died within 79 months of diagnosis [6] and two out of 13 patients with follow-up data died with respiratory problems in the series by Capizzi et al. [2].

Tracheobronchial amyloidosis is usually of the AL type [1], without evidence of other amyloidosis localisation, detectable lymphoma or monoclonal gammapathy, although some exceptions have been reported [2]. Detection of a B-cell clone in localised amyloidosis has been difficult. In our patient, the lymphoproliferation was not detectable by histopathology and required molecular biology techniques for detection. Moreover only one of our two tracheal samples showed the clonal cell population, which suggests that the number of cells is limited in the samples studied. We could study one other patient with AL-type tracheobronchial amyloidosis but could not demonstrate a dominant B-cell clonal population by PCR in a fresh, frozen tracheal biopsy. Analysis of stored, fixed, nonfrozen biopsies in two more patients gave no interpretable results. If molecular analysis is to be performed, we suggest analysing two or more frozen biopsies, obtained at different sites.

Therapy for tracheobronchial amyloidosis lacks consensus. However, systemic chemotherapy is commonly accepted for systemic AL amyloidosis [7] and local intervention for its localised forms [1]. Endobronchial management of tracheobronchial amyloidosis is preferred for symptomatic patients, with laser desobstruction and stenting if needed.

The association of an aetiological treatment targeting the B-cell population responsible for the continuing deposit of amyloid fibrils remains up for discussion. External beam radiation to the tracheobronchial tree, probably targeting monoclonal plasma cells, has been effective for tracheobronchial amyloidosis [8]; however, the improvement may be modest, and the long-term side-effects of radiation might be a concern [9]. Because we detected a monoclonal B-cell, we considered that the patient had low-grade lymphoma that could be treated with rituximab alone. Rituximab has been investigated as a first-line therapy for low-grade lymphoma. However, in our case, the B-cell clone was still detectable in bronchial biopsies 1 yr after rituximab treatment, which suggests that rituximab alone could not clear the monoclonal B-cell population. Clonality analysis demonstrated a clonal B-cell proliferation but did not determine the stage of differentiation. Amyloidosis may be related to plasma cell proliferation and plasma cells do not express CD20, which could explain the persistence of positive clonality after rituximab therapy. Furthermore, the clone surrounded by a large amount of amyloidosis may be inaccessible to intravenous rituximab therapy.

Therapy for tracheobronchial amyloidosis remains to be established. Future treatments could combine endobronchial management of complications with an aetiological therapy targeting the B-cell clone, as well as antibodies to the serum amyloid P component to increase the clearance of the insoluble protein fibrils [10].

We report herein for the first time an association between tracheobronchial amyloidosis and a local B-cell clonal proliferation without any other localisation of amyloidosis or clonal proliferation. This case confirms data on the pathophysiology of localised amyloidosis and highlights the need for specific evaluation of therapy to treat the disease.

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