Fragility fractures and bone mineral density in male patients affected by type 1 and type 2 myotonic dystrophy

Myotonic dystrophy is a multisystemic disorder affecting skeletal muscle. Male patients have an increased risk of fractures and develop a number of endocrine/metabolic impairments known to adversely affect bone health. The aim of this study was primarily to determine the occurrence of fragility fractures and the bone mineralization status (lumbar spine, hip and total body by dual X-ray absorptiometry) in 36 male patients affected with type 1 myotonic dystrophy and 13 male patients affected with type 2 myotonic dystrophy. Fragility fractures occurred in 15 type 1 and 7 type 2 myotonic dystrophy in non-classical osteoporotic sites, such as metatarses. Hip osteopenia was the most frequent finding, particularly in type 2 (n = 6) than type 1 myotonic dystrophy patients (n = 1), while osteoporosis was rare. Patients with type 1 myotonic dystrophy presented higher total body bone mass density than patients with type 2 myotonic dystrophy and healthy controls and lumbar spine was associated positively with the severity of the disease. Gonadic failure, with low testosterone and reduced INSL3 levels, visceral adiposity and insulin resistance correlated with reduced body mass index in both type 1 and type 2 myotonic dystrophic patients. The independent determinant of fragility fractures were low total body mass index, low blood testosterone and low global muscle mass.