The importance of complete screening for amyloid fibril type and systemic disease in patients with amyloidosis in the respiratory tract.

BACKGROUND: Patients with symptomatic thoracic involvement by amyloidosis are virtually all of AL-type, and have historically been divided into systemic and localised disease, a subdivision that helps predict outcome and aids management. Assessment and classification of amyloid has evolved in recent years to include a variety of tests, including radiolabelling of the serum amyloid P component (SAP scan) to assess anatomical distribution and immunohistochemical studies to assess fibril subtypes. Furthermore, CT scanning is now a frequent investigation for the diagnosis of thoracic disease. We wished to determine the value of these investigations on the management of such patients with amyloidosis.

METHODS: Clinicopathological data, including immunohistochemical analysis, CT scans and SAP scan results, were retrospectively reviewed from patients presenting with amyloidosis in the respiratory tract. These were then analysed to determine their impact on classification and prognosis.

RESULTS: Seventeen patients over ten years were identified, one case being related to metastatic medullary carcinoma of the thyroid. Of the remaining 16 cases, one was shown to have hereditary amyloid of transthyretin-type (TTR) on immunohistochemistry, altering management. The remaining 15 cases were AL-type, with 6 cases being classified as localised and 9 cases as systemic, after evaluation for serum and/or urine monoclonal products, cardiac involvement via echocardiography, plasma cell abnormalities on bone marrow examination, CT scan and SAP scan. 3/3 patients with localised AL-type disease had a negative SAP scan, whilst 3/5 patients with systemic AL-type disease had a positive scan. SAP scan of the patient with TTR-type disease provided information on extent of disease and supported the diagnosis by the pattern of distribution. Using CT scans to discriminate between localised and systemic disease showed a significant association with mortality at 2 years (p = 0.03).

CONCLUSION: Although the majority of symptomatic patients with pulmonary amyloidosis have AL-type disease, immunohistochemical confirmation is necessary in order not to miss rarer subtypes with completely different treatment regimes. Furthermore, a comprehensive evaluation, including SAP scan and CT scan of the thorax, in conjunction with echocardiography, bone marrow, serum and urine studies, needs to be undertaken in order to achieve maximum accuracy with regard to localised and systemic disease.