Bone disease may be investigated by
- blood tests (serum calcium, phosphate, alkaline phosphatase and 25 hydroxy vitamin D - (25OH vit D) - and Parathormone - PTH)
- imaging (radiographs) - for evidence of skeletal dysplasia
- bone density (DXA)
- genetic tests (collagen genes)
Examples of bone disease are described in the conditions below
Osteomalacia / Rickets - In young children, Vitamin D deficiency presents with failure to thrive, limp, aches and pains, bow legs and myopathy (proximal weakness).
Primary osteoporosis - Osteogenesis imperfecta (OI) are a group of inherited abnormal collagen conditions, resulting in abnormal type 1 collagen (the major protein found in bones, ligaments and tendons). This manifests in bone fragility, with bowing, low trauma fractures and hypermobility. In the most common form (type I), which is autosomal dominant, there are fractures during childhood, often after minor trauma, a typical blue appearance to the sclerae. Some children develop hearing loss and may have abnormal teeth. Treatment with bisphosphonates reduces fracture rates. There is a severe, lethal form (type II) with multiple fractures which occur before birth and many infants are stillborn; Inheritance is autosomal recessive or due to new mutations.
Secondary osteoporosis - occurs in any inflammatory chronic conditions (e.g Juvenile Idiopathic Arthritis) and may increase fracture risk, often after low trauma. The use of glucocorticoids may increase fracture risk, especially with prolonged use at high doses. Other chronic conditions which result in prolonged immobility and disuse atrophy - such as Duchenne muscular dystrophy – can cause low bone mass - the effects are exacerbated with use of glucocorticoids. Endocrine problems such as anorexia nervosa, thyroid disease, Turner’s syndrome can cause osteopenia and osteoporosis. Chronic liver and kidney diseases may also cause osteoporosis.
Densitometry (DXA) - is most commonly used to assess bone density, with adjustment needed for skeletal size. Sequential measurements (usually 2 yearly) are used to monitor progress. It is important for paediatricians to be familiar with the interpretation of DXA using z scores (i.e. matching for age and gender normal values). International consensus guidance is available on use, interpetation and limitations of DXA.
The MRI below shows vertebral collapse (arrow) due to osteoporosis
These may present with bone pain or joint deformity such as swelling. They may be suggested by short stature, joint contractures and pain often with a positive family history. The photographs below show symmetrical swellings on the medial aspect of a child's lower leg and the radiographs demonstrate bone exostoses due to skeletal dysplasia.
The photograph below shows symmetrical bony swelling and deformity in skeletal dysplasia