Increased oxidative stress in obstructive sleep apnoea is thought to contribute to endothelial dysfunction. The objective of this study was to test the hypothesis that inhibition of xanthine oxidase by allopurinol can improve endothelial function in patients with obstructive sleep apnoea. A randomised double-blind placebo-controlled crossover study was performed on 12 patients with moderate-to-severe obstructive sleep apnoea, comparing 300 mg allopurinol daily for 2 weeks with placebo. Endothelial function was assessed using hyperaemia-induced flow-mediated vasodilation (FMD) at baseline and following treatment. Plasma malondialdehyde levels were compared in order to assess significant changes in oxidative stress. Baseline FMD correlated significantly with the severity of sleep apnoea and the time spent with an arterial oxygen saturation of <90%. Allopurinol caused a significant increase in FMD compared to placebo (10.4+/-3.2 versus 7.4+/-2.8%, respectively). Plasma malondialdehyde levels were significantly reduced with allopurinol treatment (1.5+/-0.3 versus 1.2+/-0.3 micromol.L(-1)), consistent with reduced oxidative stress. Allopurinol improves endothelial dysfunction in patients with moderate-to-severe obstructive sleep apnoea. These observations suggest that xanthine oxidase contributes significantly to vasodilatory impairment.

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Graves' disease is an autoimmune process in which the thyroid gland is stimulated by autoantibodies, leading to hyperthyroidism. Graves' disease is the most common cause of hyperthyroid function, primarily affecting women in their 40s and 50s. Treatment may involve oral radioiodine, which is taken up by the follicular cells of the thyroid, where it emits ionizing radiation to promote destruction of those cells. Radioiodine therapy is typically safe, effective, and inexpensive. We describe the case of a 51-year-old woman who developed acute promyelocytic leukemia within 27 months of completing a cumulative dose of radioiodine 22.1 mCi (817.7 MBq) for treatment of Graves' disease. Assessment of causality using the Naranjo probability scale showed that a possible relationship existed between this patient's acute promyelocytic leukemia and the use of radioiodine. Strict hematologic follow-up of patients treated with radioiodine may be warranted, along with a high index of suspicion in those with coagulopathy.