Case Presentation: A 61-year-old woman initially presented to our clinic with a sternal fracture after “being hugged too tightly” by a friend. Her physical exam was notable for tenderness to palpation over the 4th intercostal space bilaterally. Sternal x-ray showed a non-displaced fracture along with diffuse demineralization of her sternum. Subsequent DXA scan showed osteoporosis of the lumbar spine (T-score -3.5) and osteopenia in the femoral neck (T-score -1.8) and total hip (T-score -1.7). Her workup for secondary causes of osteoporosis was normal. The patient declined traditional medical therapies and instead wanted to pursue treatments primarily with her integrative medicine doctor, in addition to calcium and vitamin D supplementation.Three years later, she had a DXA for continued monitoring of her osteoporosis. Surprisingly, bone densitometry showed osteopenia of the lumbar spine (T-score -1.6), normal hip (T-score -0.4) and normal femoral neck (T-score -0.7). This demonstrated a remarkable increase of 20% in hip bone density and 31.7% in lumbar spine bone density in only three years. Review of her herbal supplements showed that, in addition to calcium and vitamin D, she had been taking Growth Factor S, which notably contains 680 mg of elemental strontium.
Discussion: Strontium ranelate is commonly sold as an over the counter supplement in the United States for bone health and has been approved in Europe to help treat osteoporosis. Strontium mineralizes into bone over time and becomes incorporated into the skeleton. It has a higher attenuation than calcium when measured using bone densitometry, which can overestimate true bone density (1). This can lead to a false elevation in dual-energy X-ray absorptiometry (DXA) scans, making disease monitoring for osteoporosis difficult and misleading.
Conclusions: This case illustrates the artificial elevation in bone densitometry that may occur with supplementation of strontium. Because strontium attenuates X-rays more strongly than calcium, bone mineral density may be incorrectly reported. Although an actual improvement in bone density may exist, the strontium can cloud the picture, making it difficult to monitor true disease progression. Strontium may cause false elevations for up to 10 years despite discontinuation of the supplement. In addition, studies suggest that strontium mainly thickens the outer cortical bone, which reduces the tensile strength of the bones and may make them more prone to fracture (1). It is therefore critical to recognize the possibility of inaccurate DXA scans for years following initiation of strontium supplements. Physicians should be wary of large increases in bone density in short time intervals and be sure to ask patients about strontium supplementation.