A multidisciplinary approach to investigate the manifestations of Diffuse Idiopathic Skeletal Hyperostosis (DISH) in modern South African skeletal remains

Abstract

Diffuse idiopathic skeletal hyperostosis (DISH) is a pathological condition that primarily affects the spine. The focus of this study was to investigate the possible link between a diet rich in animal proteins and DISH using carbon and nitrogen isotope analysis, while also making observations on the development and underlying structure of the spinal manifestations of individuals diagnosed with DISH using micro-computed tomography (micro-CT). This investigation into DISH was undertaken in three steps. Firstly, a macroscopic analysis of DISH was conducted to identify individuals diagnosed with DISH according to accepted diagnostic criteria from three cadaver-derived South African skeletal populations (including the Pretoria Bone Collection, The Raymond A. Dart Collection of Human skeletons, and the Kirsten Collection of Human remains). Secondly, stable isotope ratios (δ¹3C and δ¹⁵N) were measured from human bone collagen samples (rib and femur), to investigate the relationship between diet and DISH, specifically a diet high in animal protein. The isotopic values (δ¹3C and δ¹⁵N respectively) were compared for both the rib and femur samples jointly and separately, between the DISH group and a control group, to see if differences existed according to sex, ancestry, BMI, BMI and ancestry combined and collection source. Thirdly, the underlying structure associated with the calcification/ossification associated with DISH (in the spine) was assessed using micro-CT scanning. Across all three skeletal collections, 127 (77% male and 23% female) individuals had characteristics associated with DISH (3.3%), with no difference in prevalence between males and females. DISH was found to be most prevalent among white South African males, indicating something (perhaps genetic or cultural) within the group, giving rise to their propensity to developing the disease. No association between BMI classification and prevalence of DISH was found. Stable isotope analysis indicated that while individuals with DISH generally had elevated δ15N values, but δ15N was also high among the control group, with both groups displaying a mean of 13.0‰. Most black South Africans diagnosed with DISH were enriched in δ¹3C, but relatively depleted in δ¹⁵N, while the white and coloured South Africans showed a positive correlation between δ¹⁵N enrichment and δ¹3C enrichment. Within the DISH group, overweight individuals were generally more enriched in δ¹⁵N and depleted in δ¹³C, while the underweight individuals were more enriched in δ¹³C and depleted in δ¹⁵N. The isotope analyses presents a complex narrative between diet and DISH. While elevated δ15N values among individuals diagnosed with DISH could be interpreted as consumption of animal protein, it was not exclusive to those with DISH and was also noted in non-DISH individuals. Any variations in the δ¹3C and δ15N values found between the DISH and control groups are most likely reflecting different dietary patterns, associated with temporal changes, cultural practices, religious and economic factors, independent of DISH. Observations from the micro-CT scans corroborate some of the clinical interpretations within the literature, such as flowing ossification being limited to the right lateral portion in the anterior aspect of contiguous vertebrae (except in one case where situs inversus was a possibility) and retention of the intervertebral disc space. In contrast to the literature, a possible erosive/inflammatory process was noted in the spinal development of DISH, preceding new bone formation. This was characterised by the destruction of the original vertebral wall underneath the fluid ossification/new bone formation. In summary, the finding from the micro-CT scans is worth further exploration in future research, while the isotopic analysis lends no support to the theory that the presence of DISH is associated with a diet high in protein.