Objectives/Goals: Amyloid deposition in the ligamentum flavum (LF) is associated with LF hypertrophy and resulting lumbar stenosis (LS) in some patients. Whether amyloid causes inflammation and subsequent fibrosis in the LF is unclear. An association between amyloid and markers of inflammation may present an opportunity to treat early stenosis with medical therapy. Methods/Study Population: LF specimens from 66 patients with lumbar stenosis (LS) were analyzed, including 33 amyloid-positive and 33 amyloid-negative patients matched by age and diagnosis. We performed immunohistochemistry on 7 tissue sections per specimen for biomarkers of inflammation (IL-6, C9) and fibrosis (Collagen, Elastin, TGF-β1, α-SMA, ROCK1). All biomarkers were quantified using a validated random forest classifier in QuPath. In Aim 1, we compared the collagen-to-elastin ratio between groups as an indicator of fibrosis, with secondary comparison of the collagen and elastin percent (α=0.025 each, Bonferroni corrected). In Aim 2, we will compare expression of IL-6, C9, TGF-β1, α-SMA, and ROCK1 using a multivariate mixed-effects regression model to identify inflammatory and fibrotic patterns linked to amyloid deposition. Results/Anticipated Results: This study tests the hypothesis that amyloid deposition in the ligamentum flavum (LF) drives fibrosis, and the resulting LF hypertrophy and lumbar stenosis (LS), via an inflammatory pathway. Aim 1 analyses are complete, and amyloid-positive LF demonstrated a higher collagen-to-elastin ratio, with a mean difference of 0.31 (0.07–0.55, p = 0.014). This difference is driven by elastin, which covers 7.5% less tissue area in amyloid-positive LF (p = 0.008). This is the first histological evidence that amyloid is associated with altered extracellular matrix composition in the LF. We hypothesize that amyloid-positive LF will show elevated expression of IL-6 and C9, comparable TGF-β1 and α-SMA, and lower ROCK1, supporting an inflammatory pathway to LF hypertrophy distinct from pathways triggered by mechanical stress. Discussion/Significance of Impact: This work will provide evidence on a possible role of amyloid in the pathophysiology of LS in a subset of patients. Our results will guide more robust quantitative analyses, including proteomics and transcriptomics, and for the first time, may support trial of anti-amyloid medical therapies to slow the progression of this primarily surgical disorder.
Patel et al. (Wed,) studied this question.