Background AA amyloidosis (AAa) is one of the most insidious systemic complications of rheumatoid arthritis (RA), which furtively may lead to death [1].

Objectives The aim of this study was to determine the prevalence and location of amyloid A deposition in the lungs of RA patients at the time of death.

Methods A randomized autopsy population of 161 in-patients with RA was studied. AAa complicated RA in 34 (21.1%) cases [1].

At least four tissue samples of lungs (from apical and basal regions of both lungs) were available for histologic evaluation in 33 of these 34 patients.

RA was confirmed clinically according to the criteria of the ACR.

The presence of amyloid A deposits in various structures of the lungs was determined histologically by amyloid specific Congo red staining, according to Romhányi [2].

The extent of amyloid A deposition was evaluated by semi-quantitative, visual estimation on a 0 to 3 plus scale, based on the number of involved tissue structures per light microscopic field [1]. (“0”: no amyloid deposits, “1”: Sporadic, minimal amyloid deposits on different tissue structures, “2”: less than five, “3”: five or more involved tissue structures per microscopic field at objective magnification of x20)

Results Amyloid A deposition in the lungs was detected in 24 of 33 (72.2%) patients.

Amyloid deposition in various structures does not begin at the same time.

In the early stage of systemic amyloidosis there were histologically detectable amyloid deposits only in a few structures (arterioles, interstitial collagen fibers, peribronchial and perilobular basement membranes). In other structures (small and medium size arteries, panlobular basement membranes, small veins, collagen IV reticulin fibres, venules, medium size veins and nerves) deposits were seen only in late stages of amyloidosis (with massive involvement of the mentioned structures).

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Conclusions Amyloidosis is a progressive, cumulative process, involving in its early stage only a few structures in some organs, and increasingly more in the later stages of the disease [1]. Amyloid A deposition starts in the most frequently involved structures of the most frequently involved organ [1].

In the lungs amyloid A deposition starts in the wall of arterioles and in interstitial collagen fibers. As time progresses, basement membranes of peribronchial and peripheral regions of lobules, small and medium sizes arteries become involved. Still later panlobular deposition of basement membranes, small veins, reticulin fibers (collagen IV) of subpleural fat tissue, venules and medium size veins become involved. The involvement of nerves indicates advanced stages of amyloid deposition in the lung.

This chronology of amyloid A deposition allows an indirect assessment of the stage of amyloidosis. Based on the involvement of structures in lung biopsy specimens the pathologist may be able to estimate involvement of the other structures, even if not present in the sections. Involvement of arterioles alone (without involvement of small arteries) indicates an early stage of amyloidosis, whereas amyloid A deposits in veins or peripheral nerves suggests an advanced stage with massive involvement of other pulmonary structures.

References

1. Bély M, Apáthy Ά: Clinical pathology of rheumatoid arthritis: Cause of death, lethal complications and associated diseases. 1–440 pp. Akadémiai Kiadό, Budapest 2012 http://www.akkrt.hu.

2. Romhányi G (1971) Virchows Arch 354, 209–222.

References

Disclosure of Interest None declared