Denosumab Treatment of Severe Disuse Osteoporosis in a Boy With Spinal Muscular Atrophy.

Denosumab is a fully human recombinant monoclonal antibody to the receptor activator of nuclear factor-κB ligand. Denosumab is used in the treatment of postmenopausal osteoporosis and cancer-related bone disorders. There are only very scarce data on denosumab treatment in children. 14-year-old boy with spinal muscular atrophy (SMA) and severe disuse osteoporosis (spinal bone mineral density L1-L4 BMD-6.2SD Z-score) and two prevalent fragility fractures was treated with denosumab. He received 60 mg  subcutaneous injection at the baseline and seven months later. Six months after the initial injection there was a 19% increase in L1-L4 BMD. The injections were well tolerated without any adverse reactions. Calcemia remained stable (2.3-2.4 mmol/L). He was scheduled for the third denosumab injection six months later. Prior to this date, he acquired pneumonia and died due to respiratory failure, which is a frequent cause of death in patients with SMA. There was no relation to the denosumab treatment. In conclusion, one dose of denosumab significantly increased BMD in a child with severe osteoporosis.