Is Platelet-Derived Growth Factor-BB Expression Proportional to Fibrosis in the Hypertrophied Lumber Ligamentum Flavum?

In Brief Study Design. A clinical and experimental assessment using human samples of lumbar ligamentum flavum (LF). Objective. To identify platelet-derived growth factor-BB (PDGF-BB) expression in hypertrophied LF of patients with lumbar spinal canal stenosis (LSS) and relate it to fibrosis. Summary of Background Data. Recent studies showed that fibrosis in LF hypertrophy was due to accumulation of inflammation-related scar tissue. PDGF-BB participates in scar formation and collagen development in wound healing and fibrosis diseases. However, it is unclear whether PDGF-BB expression is associated with fibrosis of the hypertrophied LF in LSS. Methods. In all, 10 patients of LSS was enrolled in this study, while 10 patients of lumbar disc herniation (LDH) as a control group. LF thickness was measured by axial T1-weighted magnetic resonance imaging. Fibrosis was graded and type of collagen was identified. The location and the expression of PDGF-BB were analyzed using immunohistochemical stains, real-time polymerase chain reaction, and Western Blotting. Correlation among LF thickness, fibrosis, and PDGF-BB expression was analyzed. Results. LF thickness was 5.3 ± 1.0 mm (range from 3.9 to 7.5 mm) in the LSS group and 2.8 ± 0.7 mm (range from 1.69 to 3.8 mm) in the LDH group. Obvious fibrosis was observed in all samples of the LSS group, and correlated to LF thickness of the dural, middle, and dorsal layers (P < 0.05), respectively. PDGF-BB was detected in the hypertrophied LF, particularly in the dorsal layer. PDGF-BB expression was higher in the LSS group than that in the LDH group (P < 0.05), and in the dorsal layer than the dural layer in the LSS group (P < 0.05). PDGF-BB mRNA correlated significantly to thickness of LF (r = 0.41) and the severity of fibrosis (r = 0.69) (P < 0.05). Conclusion. A higher PDGF-BB expression existed in the hypertrophied LF of patients with LSS and could be a risk factor of the fibrosis. PDGF-BB expression was significantly higher in the ligamentum flavum (LF) in patients with lumbar spinal stenosis, especially in the dorsal layer. Fibrosis, consisting of collagen I and collagen III, was observed in the entire area of hypertrophied LF, particularly in the dorsal layer. The expression of PDGF-BB increased with fibrosis and thickness of the hypertrophied LF.