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Propionibacterium acnes infected intervertebral discs cause vertebral bone marrow lesions consistent with Modic
Stefan Dudli1, Ellen Liebenberg1, Sergey Magnitsky2
1Department of Orthopaedic Surgery, University of California San Francisco, 513 Parnassus Avenue, Suite-1164, San Francisco, 94143, California.
Abstract:
Modic type I change (MC1) are vertebral bone marrow lesions adjacent to degenerated discs that are specific for discogenic low back pain. The etiopathogenesis is unknown, but occult discitis, in particular with Propionibacteria acnes (P. acnes), has been suggested as a possible etiology. If true, antibiotic therapy should be considered for patients with MC1. However, this hypothesis is controversial. While some studies report up to 40% infection rate in herniated discs, others fail to detect infected discs and attribute reports of positive cultures to contamination during sampling procedure. Irrespective of the clinical controversy, whether it is biologically plausible for P. acnes to cause MC1 has never been investigated. Therefore, the objective of this study was to test if P. acnes can proliferate within discs and cause reactive changes in the adjacent bone marrow. P. acnes was aseptically isolated from a symptomatic human L4/5 disc with MC1 and injected into rat tail discs. We demonstrate proliferation of P. acnes and up-regulation of IL-1 and IL-6 within three days of inoculation. At day-7, disc degeneration was apparent along with fibrotic endplate erosion. TNF-α immunoreactivity was enhanced within the effected endplates along with cellular infiltrates. The bone marrow appeared normal. At day-14, endplates and trabecular bone close to the disc were almost completely resorbed and fibrotic tissue extended into the bone marrow. T-cells and TNF-α immunoreactivity were identified at the disc/marrow junction. On MRI, bone marrow showed MC1-like changes. In conclusion, P. acnes proliferate within the disc, induce degeneration, and cause MC1-like changes in the adjacent bone marrow. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1447-1455, 2016.
Insights
Propionibacteria acnes (P. acnes) infection may cause Modic type I changes (MC1) in the spine. This study demonstrates P. acnes proliferation in discs, leading to degeneration and MC1-like bone marrow changes in rats.
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.
