Lumbar Disc Degeneration, A Transdifferentiation Process-An Electron Microscopic Observation

Lumbar Disc Degeneration, A Transdifferentiation Process-An Electron Microscopic Observation

Prashant B Lakhe
GIPMER, New Delhi, India

Introduction: Lumbar disc degeneration (LDD)is a common condition which affects quality of life. Repeated trauma, ageing and stress predispose to LDD. However exact mechanism is not fully understood. Transdifferentiation refers to a process where a one mature cell switches its phenotype and function to that of another mature differentiated cell type. Such mechanisms have been described in repair following fracture of bones. In order to understand it better, we conducted an electron microscopic study to analyze if LDD is a transdifferentiation process.

Methodology: After institutional ethics committee approval, patients who presented with LDD were subjected to preoperative MRI. Failure of medical management, and occurrence of neurological deficits formed the indication for surgery. Discoidectomy was done by standard microscopic techniques and the disc material was examined under electron microscopy. The disc material was collected and labelled according to proximity to adjoining osteophyte formation. The electron microscopic findings were correlated with clinical and radiological observations.

Results: Study was conducted from Jan 2020 – Dec 2021. A total of 50 patients with 28 males ,22 females with a mean age of 47 years were studied. Majority of the patients(26) had a prolapse at L4- 5 level with the mean duration of symptoms being 12 months. 80 % of patients had a VAS score of 7 and 8. Maximum (72 %) patients showed a Pfirrmann grade 4 of degeneration on MRI and type 2 Modic changes (64 %). Ten patients(20%) showed presence of posterior osteophytes. Electron microscopy showed chondrocyte clustering in 92 % patients, collagen abnormalities in 66% and intracellular inclusions in 60%. Chondrone formation was seen in 12 patients. Patients with higher pain severity and longer duration of symptoms showed increased chondrocyte clustering. Osteophyte formation was seen in patients with longer duration of symptoms. All the patients with osteophytes showed presence of chondrones.

Discussion: LDD is a process which can be explained on electron microscopy. Higher VAS score and longer duration of symptoms results in more chondrocyte clustering. In addition, formation of osteophytes was always associated with chondrone formation. These findings support our hypothesis that lumbar disc degeneration is a transdifferentiation process.

Keywords: lumbar disc degeneration, transdifferentiation, chondrocyte clustering, chondrone