Amyloidosis affecting peripheral nerves causing isolated nerve palsies is uncommon. Localised amyloidosis occurs less frequently than the reactive or immune related systemic forms, and mediastinal localisation is virtually unknown. We present a case of recurrent laryngeal nerve palsy associated with mediastinal AL amyloidosis in a middle aged man.
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A 64 year old white retired bricklayer presented with a three week history of hoarseness and a five week history of dysphagia for solids. Apart from his hoarseness, physical examination was non-contributory. Chest radiography showed a grossly widened mediastinum. Despite a normal Kveim test and bronchial and transbronchial biopsy specimens, he had an unproven diagnosis of sarcoidosis based on a chest radiograph performed 17 years previously showing bilateral hilar lymphadenopathy and bilateral upper lobar nodular shadowing. Computed tomographic scanning showed a large calcified mass in his superior mediastinum surrounding the trachea, the aortic arch, compressing the left brachiocephalic vein, and associated with bilateral calcified upper lobe masses (fig 1). A barium swallow showed a small upper oesophageal posterior diverticulum but no hold up of barium. His erythrocyte sedimentation rate (ESR) was 30 mm/h and lactate dehydrogenase (LDH) levels were 1030 U/l, but his serum angiotensin converting enzyme level was only mildly raised and serum calcium and phosphate levels were normal. Fibreoptic laryngoscopy revealed a paralysed left vocal cord. A right sided thoracoscopic biopsy of the mediastinal mass stained positively for amyloid with Congo Red and displayed apple-green birefringence with high intensity cross polarised light microscopy. It did not stain with antiserum against either serum amyloid A or immunoglobulin light chains, a result completely consistent with a diagnosis of AL amyloidosis. An associated inflammatory cell reaction consisted of small lymphocytes with only occasional typical plasma cells. No plasma cell dyscrasia or lymphoproliferative disorder was seen histologically. Bence Jones proteinuria was not demonstrated, but serum monoclonal immunoglobulin G lambda (λ) light chain paraprotein was present. A serum amyloid P-component scan, prostatic and bronchial biopsy specimens were all negative, suggesting that the mediastinal amyloidosis was localised. Bone marrow biopsy specimens were also normal. Over the next two months his dysphagia resolved spontaneously. His hoarseness was improved greatly by teflon injection of the left vocal cord and speech therapy. One year after the biopsy there is no clinical or radiological progression of the disease and no further treatment is considered at this stage.
Amyloid is described as an homogeneous, proteinaceous, eosinophilic fibrillar deposit in various tissues. However,x ray diffraction accurately identifies the amyloid fibril by its unique β-pleated sheet conformation.1 Diagnostic characteristics are: (1) apple-green birefringence of Congo Red stained tissue under polarised light, (2) bright yellow-green fluorescence in thioflavine stained preparations, and (3) ultrastructural demonstration of 7–10 nm non-branching fibrils of indeterminate length.2 3 Primary immunoglobulin light chain (AL) amyloid occurs in its localised form in extramedullary plasmacytomas of the upper airways and gastrointestinal tract. However, localisation of amyloid to the mediastinum is rare, with only two cases reported as the AL type4 and one as the reactive (AA) form.5 Although calcific changes were evident on the chest radiograph, both bronchial and transbronchial biopsy specimens were normal. No histological diagnosis has been obtained of the upper lobe lesions but they are also considered to be amyloid deposits.
It is possible that the earlier chest radiographic findings diagnosed as sarcoidosis could represent early amyloid deposits, although the radiographic changes are typical for sarcoidosis.
Apart from carpal tunnel syndrome associated with β2-microglobulin deposition in haemodialysis patients, amyloid rarely affects the peripheral nervous system and is usually of the λ type, being of monoclonal origin in 85% of cases.6 Familial patterns of amyloid mixed peripheral polyneuropathy have been described, commonly associated with variant plasma transthyretin.7 This case of recurrent laryngeal nerve palsy associated with amyloidosis may be due to perineural infiltration or compression. Infiltration of the vagus nerve itself with amyloid may account for both the vocal cord paralysis and oesophageal dysmotility.
The mediastinal “amyloidoma” may represent an underlying lymphoplasmacytoma or a subtle plasma cell dyscrasia such as a Castleman's disease tumour of the solitary plasma cell variety, although this patient had no constitutional symptoms or signs of a POEMS syndrome. No steroids or cytotoxic treatment have been considered. Technically challenging surgical resection of this amyloid mass is best reserved for severe compressive and obstructive symptoms of the vascular, upper airway, or oesophageal lumen. Alternatively, intraluminal stenting may be considered.
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