Osteosarcopenia

Osteosarcopenia is the coexistence of low bone mass (osteopenia or osteoporosis) and sarcopenia. The two conditions interact, and together they cause more falls, fractures and disability than either alone.

It affects an estimated 5% to 20% of older adults, with higher rates in women after the menopause and in people with a hip fracture.

Pathophysiology. Muscle and bone share mechanical loading, hormonal control and signalling molecules (myokines such as irisin, IGF-1). Vitamin D deficiency, low sex hormones, chronic inflammation, low protein intake and inactivity damage both tissues at once.

Frequent falls, fragility fractures (hip, vertebra, wrist), loss of height, thoracic kyphosis, weakness, slow gait and loss of independence. Fractures after a fall are more likely because weak muscles fail to protect the skeleton.

Measure bone mineral density by dual energy X-ray absorptiometry (T-score of -2.5 or lower is osteoporosis, between -1 and -2.5 is osteopenia) and estimate fracture risk with a validated tool. Add grip strength, chair stand, gait speed and appendicular lean mass. Check calcium, phosphate, alkaline phosphatase, 25-hydroxyvitamin D, parathyroid hormone, creatinine, thyroid function and serum protein electrophoresis; consider coeliac serology.

Differential diagnosis.

• Secondary osteoporosis (hyperparathyroidism, hyperthyroidism, myeloma, corticosteroid use, hypogonadism).
• Osteomalacia with proximal myopathy.
• Metastatic bone disease.

Treat both conditions. Give resistance and balance exercise, protein 1.0 to 1.2 g/kg daily, dietary calcium to a total of 1000 to 1200 mg daily and vitamin D 800 to 2000 IU daily. For osteoporosis or a fragility fracture, start alendronate 70 mg orally once weekly (with eGFR above 35 mL/min), or zoledronic acid 5 mg intravenously once yearly after vitamin D is replete, or denosumab 60 mg subcutaneously every 6 months. Do not stop denosumab without follow on treatment because of rebound vertebral fractures.

Special groups. Check dental health before bisphosphonate or denosumab. Report new thigh or groin pain, which may precede atypical femoral fracture.

Monitoring. Bone density every 2 years, calcium and renal function, and falls and fractures.