242. Degenerate-disc Infection Study with Contaminant Control (DISC): application of a proposed histological scoring system

Abstract

BACKGROUND CONTEXT Chronic infection of the intervertebral disc resulting in acute/chronic back pain/leg pain remains a controversial topic of ongoing spinal research, with questions surrounding commensal organisms, its role in the pathogenesis of acute and chronic back/leg pain, and the subsequent clinical implications, all pending.A systematic review by Ganko et al (2016) has estimated the true disc infection rate to be as high as 36% (n=9 studies), with P. acnes known to be the most common commensal organism, although even its role in the setting of spinal disease remains unclear, leaving a conundrum towards whether positive organism growth is of clinical value warranting treatment or intervention or if it's a contaminant. PURPOSE To validate the clinical relevance of histopathological evidence of inflammation and positive disc culture through the implementation of a previously proposed histological grading system across the microscopic presence of neutrophilia, granulation tissue, dense fibrosis and chronic inflammatory cells. STUDY DESIGN/SETTING Multisurgeon prospective cohort study at the Prince of Wales Hospital, Sydney, Australia. PATIENT SAMPLE A total of 124 consecutive patients undergoing an elective spinal decompression and/or fusion procedure involving discectomy were selected with intraoperative tissue sampling of intervertebral disc and paraspinal tissue. OUTCOME MEASURES A true positive sample was one in which growth was only observed in the disc specimen in isolation from the paraspinal sample. A false positive (contaminated) sample was defined as growth in both samples. The histopathological score was applied to all disc samples. Each domain was assessed for correlation with disc culture positivity using a chi square correlation. Agreement in domains between two senior pathologists was examined using a cohen's kappa score of agreement. METHODS Disc and paraspinal specimens were obtained intraoperatively using stringent aseptic technique. All specimens were handled with sterile instruments only and by a fresh instrument to a sterile pot that was closed immediately. Separate pots were used for the disc and paraspinal ligament tissue respectively. Laboratory specimen handling was performed with similar diligence, with samples incubated within a tight 35-37 degree range and only examined at days 7 and 14. Two senior pathologists independently assessed disc samples using the above score. When there was a disagreement in different parameters with the scoring system, further discussion and re-evaluation of microscopic findings was performed until a unanimous consensus was reached. Pathologists and microbiologists were blinded to the results of one another. RESULTS There were in total 124 disc samples (36 cervical and 88 lumbar) obtained. Of these, 29 (23.4%) disc specimens and 37 (29.8%) ligament samples demonstrated growth of P acnes. In total, 38/124 (30.6%) of disc specimens were positive for growth of any species. There was poor association between positive disc culture and the presence of neutrophilia (p=0.123) or chronic inflammatory changes (p=0.092) on histopathological assessment. There was no statistical significance noted across all histological domains examined within the finalized scoring system and positive culture across disc specimens. There was moderate agreement in between observers (kappa range: 0.41-0.60) in the assessment of inflammatory changes using the proposed scoring system. CONCLUSIONS The current study provides no correlation between histopathological evidence of chronic or acute inflammation and positive disc cultures questioning the idea that disc infection is a possible root cause of acute or chronic back pain/leg pain. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.