Evaluating Patients for Secondary Causes of Osteoporosis

Introduction to Osteoporosis, Osteomalacia, and Fragility Fractures

Background

Osteoporosis is a disease of the bones leading to decreased bone mineral density, leading to fragility fractures. This article is an overview of osteoporosis, osteomalacia and fragility fractures and serves as an introductory article for this special issue on osteoporosis.

Methods

This is a short, comprehensive account of the given conditions with concepts and a review from the recent literature. The authors provide relevant references from the literature in the bibliography. The sections herein have also been deliberated in the meetings of experts of osteoporosis.

Results

An overview of osteoporosis, osteomalacia and fragility fractures is provided, including definitions and summaries of aetiology, pathophysiology, diagnosis, prevention, and management. A detailed account of some of these topics will be provided in subsequent chapters.

Conclusion

Osteoporosis is a silent disease with the potential to cause significant morbidity and mortality if not detected early. It is important to differentiate from and diagnose associated osteomalacia to provide accurate therapy. It is also important to identify the type of fragility fractures and initiate treatment for bone strengthening to prevent subsequent fractures.

Classification of Osteoporosis

Osteoporosis is defined by low bone quality, strength and increased fracture risk. Primary and secondary osteoporosis are the two forms of osteoporosis classified on the basis of factors affecting the metabolism of bone. Primary osteoporosis develops as a result of aging or menopause-related bone demineralization. Type I/postmenopausal and type II/senile osteoporosis are two subtypes of primary osteoporosis. Secondary osteoporosis is due to pathological conditions and medications other than aging and menopause that lead to deprivation of bone mass and elevated fracture risk. Classification of osteoporosis based on BMD testing with DEXA devised by the World Health Organization utilizes T-score in BMD reporting of women in menopausal transition or postmenopause and men ≥ 50 years. Z-scores are preferred, while BMD reporting in premenopausal women, adults < 50 years of age, and children. BMD alone is not diagnostic of osteoporosis in men < 50 years. The Fracture Risk Assessment Tool Model (FRAX) is a software algorithm that incorporates significant predictors of fracture risk and BMD in individuals to predict the risk of fracture. FRAX predicts the "10-year probability of a major fracture (hip, clinical spine, humerus, or wrist fracture) and the 10-year probability of a hip fracture".

Bone quality in endocrine diseases: determinants and clinical relevance

PURPOSE

Bone is one of the main targets of hormones and endocrine diseases are frequent causes of secondary osteoporosis and fractures in real-world clinical practice. However, diagnosis of skeletal fragility and prediction of fractures in this setting could be a challenge, since the skeletal alterations induced by endocrine disorders are not generally captured by dual-energy X-ray absorptiometry (DXA) measurement of bone mineral density (BMD), that is the gold standard for diagnosis of osteoporosis in the general population. The aim of this paper is to review the existing evidence related to bone quality features in endocrine diseases, proposing assessment with new techniques in the future.

METHODS

A comprehensive search within electronic databases was performed to collect reports of bone quality in primary hyperparathyroidism, hypoparathyroidism, hyperthyroidism, hypercortisolism, growth hormone deficiency, acromegaly, male hypogonadism and diabetes mellitus.

RESULTS

Using invasive and non-invasive techniques, such as high-resolution peripheral quantitative computed tomography or DXA measurement of trabecular bone score (TBS), several studies consistently reported altered bone quality as predominant determinant of fragility fractures in subjects affected by chronic endocrine disorders.

CONCLUSIONS

Assessment of skeletal fragility in endocrine diseases might take advantage from the use of techniques to detect perturbation in bone architecture with the aim of best identifying patients at high risk of fractures.

Osteoporosis in adults in clinical practice (1): diagnosis and differential diagnosis

Osteoporosis is a systemic metabolic disease of the skeleton characterized by low bone strength that results in an increased risk of fracture. Fractures are associated with serious clinical consequences, including pain, disability, loss of independence, and death, as well as high healthcare costs. Early identification and intervention with patients at high risk for fracture is needed to reduce the burden of osteoporotic fractures. The identification of a patient at high risk of fracture should be followed by evaluation for factors contributing to low bone mineral density (BMD) and/or low bone quality, falls, and fractures. Components of the osteological evaluation include an assessment of BMD by dual-energy X-ray absorptiometry, osteoporosis-directed medical history and physical exam, laboratory studies, and possibly skeletal imaging. Disorders other than osteoporosis, requiring other types of treatment, may be found. This overview summarizes the basic procedures for the diagnosis and differential diagnosis of osteoporosis, which are necessary before starting treatment.

How to implement guidelines and models of care

In subjects older than 50 years, the presence of clinical risk factors (CRFs) for fractures or a recent fracture is the cornerstone for case finding. In patients who are clinically at high short- and long-term risk of fractures (those with a recent clinical fracture or with multiple CRFs), further assessment with bone mineral density (BMD) measurement using dual-energy absorptiometry (DXA), imaging of the spine, fall risk evaluation and laboratory examination contributes to treatment decisions according to the height and modifiability of fracture risk. Treatment is available with anti-resorptive and anabolic drugs, and from the start of treatment a lifelong strategy is needed to decide about continuous, intermittent, and sequential therapy. Implementation of guidelines requires further initiatives for improving case finding, public awareness about osteoporosis and national policies on reimbursement of assessment and therapy.

Early-Onset Osteoporosis: Rare Monogenic Forms Elucidate the Complexity of Disease Pathogenesis Beyond Type I Collagen

Early-onset osteoporosis (EOOP), characterized by low bone mineral density (BMD) and fractures, affects children, premenopausal women and men aged <50 years. EOOP may be secondary to a chronic illness, long-term medication, nutritional deficiencies, etc. If no such cause is identified, EOOP is regarded primary and may then be related to rare variants in genes playing a pivotal role in bone homeostasis. If the cause remains unknown, EOOP is considered idiopathic. The scope of this review is to guide through clinical and genetic diagnostics of EOOP, summarize the present knowledge on rare monogenic forms of EOOP, and describe how analysis of bone biopsy samples can lead to a better understanding of the disease pathogenesis. The diagnostic pathway of EOOP is often complicated and extensive assessments may be needed to reliably exclude secondary causes. Due to the genetic heterogeneity and overlapping features in the various genetic forms of EOOP and other bone fragility disorders, the genetic diagnosis usually requires the use of next-generation sequencing to investigate several genes simultaneously. Recent discoveries have elucidated the complexity of disease pathogenesis both regarding genetic architecture and bone tissue-level pathology. Two rare monogenic forms of EOOP are due to defects in genes partaking in the canonical WNT pathway: LRP5 and WNT1. Variants in the genes encoding plastin-3 (PLS3) and sphingomyelin synthase 2 (SGMS2) have also been found in children and young adults with skeletal fragility. The molecular mechanisms leading from gene defects to clinical manifestations are often not fully understood. Detailed analysis of patient-derived transiliac bone biopsies gives valuable information to understand disease pathogenesis, distinguishes EOOP from other bone fragility disorders, and guides in patient management, but is not widely available in clinical settings. Despite the great advances in this field, EOOP remains an insufficiently explored entity and further research is needed to optimize diagnostic and therapeutic approaches. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Case report: Clinical characteristics and treatment of secondary osteoporosis induced by X-linked congenital adrenal dysplasia

OBJECTIVE

To summarize the clinical features and bone complications in a patient from a large family with X-linked congenital adrenocortical hypoplasia (AHC) and evaluate the efficacy of different treatment regimens on the prognosis of secondary osteoporosis caused by AHC at a 5-year follow-up.

METHODS

A large family with AHC was recruited, and the causative gene mutation was identified by Sanger sequencing in the proband. Clinical features as well as radiological examinations and laboratory indices of osteoporosis secondary to AHC were analyzed in this study. Meanwhile, the proband was treated with classical antiresorptive drugs (bisphosphonates) for 2 years and switched to a vitamin K₂ analogue for another 3 years, during which the efficacy of the drugs was evaluated.

RESULTS

The proband was identified as carrying a homozygous insertion mutation (p. Thr193GlyfsX13) in the NR0B1 (nuclear receptor subfamily 0, group B, member 1) gene, resulting in a premature stop codon due to a frameshift mutation. During treatment and follow-up, the proband did not respond well to bisphosphonate and developed atypical femoral fractures. Vitamin K₂ improved clinical symptoms. In terms of bone mineral density (BMD), there is no evidence of any effect of vitamin K₂ on the neck of femur, though some minor effects on spinal BMD cannot be excluded.

CONCLUSIONS

Secondary osteoporosis induced by AHC deserves clinical attention. Unlike in primary osteoporosis, the curative effect of bisphosphonates was unsatisfactory and was more likely to cause atypical femoral fractures in long-term treatment. It is suggested that bone anabolic drugs may be better alternatives.