RESUMO
The phrase "skin as a mirror of internal medicine," which means that the skin reflects many of the diseases of the internal organs, is a well-known notion. Despite the phenotypic differences between the soft skin and hard bone, the skin and bone are highly associated. Skin and bone consist of fibroblasts and osteoblasts, respectively, which secrete collagen and are involved in synthesis, while Langerhans cells and osteoclasts control turnover. Moreover, the quality and quantity of collagen in the skin and bone may be modified by aging, inflammation, estrogen, diabetes, and glucocorticoids. Skin and bone collagen are pathologically modified by aging, drugs, and metabolic diseases, such as diabetes. The structural similarities between the skin and bone and the crosstalk controlling their mutual pathological effects have led to the advocacy of the skin-bone axis. Thus, the skin may mirror the health of the bones and conversely, the condition of the skin may be reflected in the bones. From the perspective of the skin-bone axis, the similarities between skin and bone anatomy, function, and pathology, as well as the crosstalk between the two, are discussed in this review. A thorough elucidation of the pathways governing the skin-bone axis crosstalk would enhance our understanding of disease pathophysiology, facilitating the development of new diagnostics and therapies for skin collagen-induced bone disease and of new osteoporosis diagnostics and therapies that enhance skin collagen to increase bone quality and density.
RESUMO
Background Although the correlation between reduced skin thickness and reduced bone density has been investigated, no study has evaluated skin thickness and osteoproliferative diseases, including ossification of the posterior longitudinal ligament (OPLL) and diffuse idiopathic skeletal hyperostosis (DISH). Methodology This retrospective cohort study consisted of 99 consecutive patients aged ≥60 years treated for spinal surgery at our hospital between January 2022 and March 2023. Skin thickness was measured at the dorsal side of the cervical, thoracic, and lumbar vertebrae on the sagittal cross-section image of whole-spine CT. Based on the median value, skin thickness was categorized into two groups based on a median thickness of 4 mm. Bone mineral density (BMD) was assessed. The sum of the vertebral body and intervertebral bridging osteophytes of the anterior longitudinal and posterior longitudinal ligament were defined as the OALL index and OPLL index. Serum levels of bone metabolism-related markers, such as tartrate-resistant acid phosphatase type 5b, procollagen I N-propeptide, 25-hydroxyvitamin D, and periostin, were measured. To assess the association between skin thickness and imaging findings, we calculated the adjusted odds ratios, adjusting for age, sex, and body mass index (BMI) and using univariate and multivariate logistic regression analyses. Results No significant differences were found in skin thickness in the three dorsal regions of the cervical, thoracic, and lumbar spine (median = 3.3 mm versus 3.5 mm versus 3.4 mm, p = 0.357) and bone metabolism-related markers. Adjusting for age, sex, and BMI, cervical, thoracic, and lumbar skin thicknesses were related to DISH, the OPLL index, and the OPLL and OPLL index, respectively. Conclusions Skin thickness did not correlate with BMD but with the amount of spinal ossification. A correlation was found between skin thickness and vertebral and intervertebral ossification; vertebral osteophytes, OPLL, and DISH may be more common in thicker skin.