Propionibacterium acnes infected intervertebral discs cause vertebral bone marrow lesions consistent with Modic...

Area of Science:

• Orthopaedic Research
• Microbiology
• Spinal Pathology

Background:

• Modic type I changes (MC1) are vertebral bone marrow lesions linked to discogenic low back pain.
• The exact cause of MC1 is unknown, but occult discitis, particularly Propionibacteria acnes (P. acnes) infection, is a suspected etiology.
• Previous studies have conflicting results regarding bacterial presence in degenerated discs, with some suggesting contamination as a source of positive cultures.

Purpose of the Study:

• To investigate the biological plausibility of P. acnes causing MC1.
• To determine if P. acnes can proliferate within intervertebral discs and induce reactive changes in adjacent bone marrow.

Main Methods:

• P. acnes was isolated from a human L4/5 disc with MC1 and inoculated into rat tail discs.
• Disc degeneration, inflammatory markers (IL-1, IL-6, TNF-α), cellular infiltrates, and bone resorption were assessed over 14 days.
• Magnetic Resonance Imaging (MRI) was used to evaluate bone marrow changes.

Main Results:

• P. acnes proliferated within rat discs, with increased IL-1 and IL-6 observed within three days.
• By day 7, disc degeneration and endplate erosion occurred, with enhanced TNF-α and cellular infiltrates in the endplates.
• By day 14, significant bone resorption and extension of fibrotic tissue into the bone marrow were noted, with T-cells and TNF-α present at the disc/marrow junction. MRI revealed MC1-like changes.

Conclusions:

• P. acnes can proliferate within intervertebral discs.
• P. acnes infection induces disc degeneration and causes Modic type I change-like alterations in the adjacent bone marrow.
• These findings support the hypothesis that P. acnes may be an etiological factor in some cases of Modic type I changes and discogenic low back pain.