Amyloid Deposits in the Ligamentum Flavum Related to Lumbar Spinal Canal Stenosis and Lumbar Disc Degeneration

Background: Amyloidosis is a protein conformational disorder, with distinctive features of accumulation of protein fibrils in different body tissues, causing a wide range of signs and symptoms. These amyloid fibrils are usually derived from about 30 different precursor proteins that have been identified. Although the most common tissue for their accumulation is cardiac, amyloidosis may appear in many other tissues, though rarely cause symptoms. One of these extracardiac tissues is the ligamentum flavum (LF). Participants and Methods: Patients with lumbar spinal canal stenosis or lumbar disc degeneration, scheduled for surgery, were included in the study. A total of 17 LF specimens were obtained from 16 patients with lumbar spinal stenosis (two specimens were taken from two consecutive stenotic levels belonging to one patient), and 11 LF specimens were obtained from 11 patients with lumbar disc degeneration. Tissue biopsy was taken from the LF at the affected level and was stained with special immunohistochemical stain to detect transthyretin (TTR)-related amyloidosis (ATTR). The diameters of the lumbar canal and the LF thickness were measured at the affected level by a radiologist. Results: This study includes 22 LF specimens. Male to female ratio was 5.4:4.6 with the mean age comparatively equal (M = 46 years for men and 48 years for women). The patients were divided into two groups: lumbar canal stenosis and lumbar disc degeneration. The result of the immunohistochemical stain towards TTR amyloid was positive in five out of 22 (22%) samples and all were from the stenosis group. The relationship of the LF thickness to the canal diameter in the positively stained stenosis group specimens was significant (p = 0.001). All the positive specimens were taken from levels L3???4 and L4???5. Conclusion: There was a significant relationship between LF thickness and canal stenosis in the positively stained specimens (towards TTR amyloid) of the stenosis group. However, the disc degeneration group showed no relationship between canal diameter and LF thickness; moreover, all the specimens of that group stained negative. Middle-age patients with canal stenosis proved to have a significant relationship to amyloid deposit LF hypertrophy.