Metabolic Bone Disease: Imaging Features

This is Paget's disease of bone, showing the classic features of enlarged bone (pathognomonic), coarse trabeculation, cortical thickening, and mixed lytic-sclerotic appearance consistent with the mixed/active phase. The bowing deformity is typical in weight-bearing bones. Complications to be aware of: (1) Pathological fracture - often transverse ('banana fracture'), (2) Secondary osteoarthritis - if near joints, (3) Sarcomatous transformation (less than 1%) - look for new aggressive lytic destruction or soft tissue mass, (4) High-output cardiac failure - if extensive skeletal involvement, (5) Nerve compression - especially if skull base involved. I would order blood tests (elevated ALP with normal calcium/phosphate in Paget's) and consider bone scan to assess extent of skeletal involvement.

This is secondary hyperparathyroidism due to chronic renal failure, showing the classic subperiosteal resorption on the radial aspect of the middle phalanges - this location is virtually pathognomonic for hyperparathyroidism. Other expected findings include: (1) Acroosteolysis - resorption of distal phalangeal tufts, (2) Brown tumours - well-defined lytic lesions in mandible, pelvis, long bones, (3) Rugger jersey spine - horizontal sclerotic endplate bands with lucent central vertebral bodies (classic for renal osteodystrophy), (4) Chondrocalcinosis - calcification in cartilage (menisci, TFCC), (5) Vascular and soft tissue calcification - due to high calcium-phosphate product. I would also assess for signs of osteomalacia component (Looser zones).

The bilateral symmetric lucent bands perpendicular to the cortex at the medial femoral necks are Looser zones (pseudofractures), which are pathognomonic for osteomalacia. In this patient with coeliac disease, malabsorption of vitamin D is the likely cause. Looser zones represent unmineralised osteoid at sites of mechanical stress. Classic locations include: medial femoral neck (as here), pubic rami, lateral scapular border, and ribs. They are bilateral and symmetric. Without treatment, they can complete into true fractures. I would order vitamin D, calcium, phosphate, PTH, and ALP levels. Treatment involves vitamin D supplementation and addressing the underlying coeliac disease. The generalised osteopenia reflects diffuse undermineralisation.