Usefulness of gastroduodenal biopsy in the differential diagnosis of systemic AH amyloidosis from systemic AL amyloidosis

Aims: The aim of this study is to examine the usefulness of gastroduodenal biopsy for the detection of immunoglobulin (Ig) heavy-chain amyloid deposition. Ig heavy-chain amyloidosis (AH amyloidosis) is Ig-related amyloidosis classified together with Ig light-chain amyloidosis (AL amyloidosis). Compared with AL amyloidosis, patients with AH amyloidosis exhibit a better prognosis and they may not need an aggressive treatment. Thus, the accurate diagnosis is essential for management of Ig-related amyloidosis patients. For the definite diagnosis of AH amyloidosis, biochemical analyses are usually needed. However, these analyses are not widely available. Therefore, the characteristic deposition pattern of AH amyloidosis in routine histopathological examination of biopsy specimens, such as gastrointestinal biopsy, if present, may help in the selection of cases for further biochemical analyses. Methods and results: Gastroduodenal biopsy specimens obtained from three cases of biochemically confirmed AH amyloidosis and 21 cases of immunohistochemically confirmed AL amyloidosis were examined, and the following distinctive histopathological features of AH amyloidosis were pointed out: (i) AH amyloid deposition was detectable with Congo red staining in the gastroduodenal biopsy specimens; and (ii) AH amyloid deposition was observed characteristically on the capillary wall of duodenal villi (dotted line-like deposition in the villi), and this pattern was not observed in AL amyloidosis. Conclusion: These findings help to select cases for biochemical analyses for definite diagnosis of AH amyloidosis, and may lead to the accumulation of cases and improve our understanding of systemic AH amyloidosis.