Background: Hyperthyroidism is associated with bone mass reduction and increased fracture risk, but the effects on other important bone parameters have been sparsely examined. Therefore, we investigated bone microarchitecture and estimated bone strength, by high-resolution peripheral quantitative computed tomography (HR-pQCT) in hyperthyroid patients at diagnosis and after being euthyroid for at least one year.Methods: Two approaches were used: A) a case-control study comparing 61 hyperthyroid women with 61 euthyroid women matched for age-and menopause status; B) a follow-up study, in which 46 of the 61 women were re-examined after having been euthyroid for one year. HR-pQCT of the distal radius and tibia, and dual energy X-ray absorptiometry (DXA) of the lumbar spine and the hip were performed.Results: In analysis A: In the radius, compared to healthy controls, hyperthyroid patients had higher total area (16.9 ±29.5%; p<0.001), trabecular area (28.6 ±45.7%; p<0.001), and lower cortical area (-11.7 ±23.2%; p<0.001). Total (-13.9 ±26.5%; p<0.001) and cortical (-

We wish to thank technicians at the Osteoporosis clinic for performing bone scans and in particular Steffanie Christensen for her help in study coordination.

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