Metabolic Bone Disease: Imaging Features

Metabolic bone disease encompasses systemic disorders that disturb the normal balance of bone formation, resorption and mineralisation. Because the abnormality is metabolic rather than focal, the imaging signs are usually generalised and bilateral, with characteristic regional accentuation that points to a specific diagnosis. The radiologist's task is to recognise the dominant abnormality — reduced quantity of mineralised bone (osteoporosis), defective mineralisation of osteoid (osteomalacia/rickets), excessive resorption driven by parathyroid hormone (hyperparathyroidism), disordered remodelling (Paget's disease), or the mixed picture of chronic kidney disease (renal osteodystrophy).

A disciplined search pattern converts a vague impression of low density into a specific diagnosis. Work through the DENSITY checklist (above): density, endplates/trabeculae, notches/resorption, soft tissue, insufficiency fractures/Looser zones, tumours, and then yield to biochemistry.

The renal osteodystrophy table lists "amyloid deposition (dialysis-related)" as a cause of bone cysts and erosions, but this is a distinct process that deserves developing. After many years of haemodialysis (typically more than 5 to 10), beta-2-microglobulin is inadequately cleared and deposits as amyloid in synovium, tendon and bone — separate from the secondary hyperparathyroidism that dominates renal osteodystrophy.

The differential table cites "osteopetrosis (sandwich vertebra)" as the mimic to exclude for rugger jersey spine, but the disease itself is never developed. Osteopetrosis is a sclerosing bone disorder caused by FAILURE of osteoclast-mediated resorption, producing diffusely dense bone that is paradoxically BRITTLE.

The classic radiographic signs of metabolic bone disease overlap with focal pathology. The decisive discriminators are distribution (generalised/symmetric vs focal), the accompanying biochemistry, and whether the affected bone is enlarged.

Metabolic bone disease is diagnosed and managed worldwide; imaging interpretation is universal, but access to DXA, scintigraphy and biochemistry varies markedly by resource setting.