Quantitative routine T2-weighted disc signal intensity index and Pfirrmann grading: age-related patterns and within-grade dispersion in a community-recruited cohort

Background Pfirrmann grading is the current standard for magnetic resonance imaging (MRI)-based characterization of intervertebral disc degeneration. However, as a qualitative, morphology-based ordinal classification, it may fail to detect early compositional change and entails information loss by reducing continuous variation in disc signal to discrete grades. A quantitative approach based on T2-weighted disc signal intensity normalized to cerebrospinal fluid, the T2 disc intensity index (T2DII), may provide a continuous marker of disc integrity. This study therefore aimed to directly compare Pfirrmann grading and T2DII for characterization of lumbar disc degeneration, with particular emphasis on age-related patterns and within-grade T2DII dispersion, while secondarily examining demographic, lifestyle, psychosocial, and cLBP-related associations. Methods Participants from the community-recruited “Berlin Back Study” cohort underwent standardized 3.0-Tesla lumbar MRI and clinical assessment. Disc degeneration at all lumbar levels was evaluated using Pfirrmann classification and T2DII. Associations between T2DII and Pfirrmann grade were assessed, and multivariable linear regression was used to examine associations with age, sex, body mass index (BMI), psychosocial factors, smoking exposure, alcohol consumption, physical activity, and cLBP status. Results A total of 577 participants (mean age, 43.0 ± 11.7 years; 58.2% women) were included. Age was strongly associated with both disc measures ( p < 0.001) but explained more variance in quantitative T2DII than in ordinal Pfirrmann grading (partial η² 0.569 vs. 0.499). Male sex was independently associated with higher T2DII (β = 3.38, p < 0.001), while cLBP status was not independently associated with either measure. In addition, within individual Pfirrmann categories, T2DII values varied widely, with the greatest dispersion in early degeneration (grades 1 to 2; IQR up to 30.46) and a progressive narrowing in advanced grades (grades 4 to 5; IQR up to 15.72; overall variance difference across grades p < 0.001). Conclusions While both measures primarily reflected age-related change, T2DII showed a stronger association with age and identified sex-related differences that were not apparent with Pfirrmann grading. Moreover, T2DII demonstrated substantial within-grade signal variation, most pronounced at low Pfirrmann grades, indicating high variability within each Pfirrmann category. Together, these findings support T2DII as a complement to Pfirrmann grading for characterizing early degenerative change and stratifying disc integrity within Pfirrmann categories, with potential relevance for risk-based monitoring and future disease-modifying interventions pending longitudinal validation.