In this cohort, 112 subjects of similar gender distribution were identified, 60% of which came from nephrology. Overall, 37% of them had osteoporotic range of BMD but this percentage varied from 10.3 to 100% amongst the subspecialties. Majority of them had bone profile screened but only a minority got vitamin D and PTH checked. Many of the patients referred for DXA had already been started on calcium and vitamin D supplements.
The diagnosis of childhood osteoprosis cannot be set based on the bone densitometric measurements alone as it requires the presence of a clinically significant fracture history. Furthermore, being a 2D measurement of BMD, DXA has its limitations. BMD of chronically ill children are often underestimated owing to the fact that they are often small built, so do their bone sizes (8). In addition, there has been no unified protocol for skeletal assessment as the clinical approach varies by specific diagnoses and expected clinical outcome. Nonetheless, it is still highly recommended as a bone health screening tool for a number of primary and secondary disorders that have been associated with low bone mass and risk of fracture (6), including Thalassemia (9), DMD (10) (11) and IBD (12), when patients may benefit from the results of densitometry.
The prevalence of some groups of our patients with osteoporotic BMD is comparable to the literature findings, namely nephrotic syndrome (13), SLE (14) and Thalassemia (15). This implies the actual number of patients that are truly osteoporotic, according to the ISCD criteria, is lower. For osteogenesis imperfecta, understandably some of the patients responded to bone-active treatment including bisphosphonate therapy as shown by improvement in their DXA. For DMD, the prevalence of osteoporotic range BMD is lower than reported (16), that is likely explained by small sample size.
All subjects in the cohort were regarded by their parent teams to be at risk of osteoporosis before they were referred for DXA. Albeit that, not necessarily they had serum 25-hydroxyvitamin D (25OHD) level evaluated (17.9% overall). Undoubtedly there shows inadequacy of 25OHD screening in some subspecialties in the cohort. Patients from neurology and endocrinology might have done it better yet their headcount was small compared to other subspecialties like nephrology. Being a recognized risk factor of fracture (17), 25OHD should be universally included in the bone health screening protocols.
Except OI and DMD, the median age of DXA scanning for all other disease groups are above 16 years. Together with the fact that over the 5-year study period, the number of active headcounts in most disease groups are greater than the cohort, it is postulated that many of the patients are deprived of the opportunity of bone health surveillance and some of them should have undergone the scan earlier. Meanwhile, some disease entities that are vulnerable to osteoporosis are absent in this cohort, e.g. patients with cerebral palsy, history of cancers, leukemia and severe asthma on high dose inhaled corticosteroids (18). This suggests the under-recognition of the importance of bone health management in certain subspecialties.
The two commonly available preparations of vitamin D supplements for prevention of osteoporosis are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Calcitriol is the most active metabolite of vitamin D and can easily lead to hypercalcemia and/or hypercalciuria (19). Therefore, calcitriol is not the drug of choice for preventing osteoporosis yet it is still being prescribed by some subspecialty teams, e.g. alongside with the prescription of long-term glucocorticoid therapy. Thus, further education of the different vitamin D preparations and sharing of experience is important in maintaining and optimizing bone health management of our patients. Paediatricians from different subspecialties may have their own judgement for arranging bone health management, including the timing of initiation and what to include in the management plan. It would be beneficial if endocrinologists could take the lead to coordinate amongst the parent teams to execute the bone health protection strategy in a more timely and complete fashion.
This review of practice serves as a pilot study aiming to cover the most needed disease groups of the hospital but not every paediatric patient, since there is a vast scope of patients that deserve bone health screening. Therefore only patients that underwent DXA were recruited as it was believed this limited group of patients was already “at risk” in their paediatricians’ mind. However, this review is also subject to a number of limitations. First, our hospital was lack of reference normative paediatric data forTBLH BMD measurement for DXA, that is also recommended by ISCD. But fortunately on the one hand vertebrae are rich in trabecular bone that is more metabolically active particularly in children, they are the most sensitive skeletal sites for BMD assessment; on the other hand, the measurement of LS and TBLH BMD are often synchronized. Second, as aforementioned, BMD of short children are underestimated owing to their smaller bone size (8). These should be adjusted for their absolute height or height age to eliminate the size-related artefacts (2), that has not been done in many places including our hospital. Third, BMC or BMD has been shown to have high specificity but low sensitivity for osteoporosis (20). Bone fragility is dependent on a multitude of factors in addition to bone mass. For example, a larger bone is resistant to fracture than a small bone, given both bones have the same BMC or BMD. Therefore, we should not solely rely on bone densitometry data to stratify patients’ risk to develop osteoporosis.
In future work, longitudinal follow-up of the same group of subjects after the coordination by endocrinologists might be helpful to prove the improvement of implementation of bone health protection strategy in the hospital. It is also recommended to replicate the study with subjects identified by the specific disease groups instead of limiting to those that have undergone DXA in order to have a more complete picture of the situation.