Axial osteomalacia: Report of a new case with selective increase in axial bone mineral density

Axial osteomalacia was diagnosed in a 60-year-old white Caucasian male, on the basis of X-ray examination showing typical coarsened and sponge-like appearance of trabecular bone strictly located in the axial skeleton. Dual energy X-ray absorptiometry demonstrated a marked increase in axial bone density at lumbar spine levels in both anteroposterior and lateral views (T score: +7.9 and +5.5, respectively), contrasting with normal values at femoral neck, trochanter and midfemoral diaphysis (T score: +0.6, +0.3, and +0.8, respectively). Histomorphometry of iliac crest showed marked thickening of cortices (1730 and 2763 μm, N = 967 ± 57), increased trabecular bone volume (28.9%, N = 17.4 ± 5.6), normal eroded surface (3.5%, N = 3.6 ± 1.1), and increased osteoid surface and volume (31.6%, N =15.3 ± 9.4 and 5.8%, N = 2.8 ± 1.8). Osteoid thickness was increased (39.6 μm, N = 10.5 ± 1.8, up to 120 pm in one site) and mineral apposition rate was decreased in the trabecular sites (0.43 μm/day, N = 0.72 ± 0.12, down to <0.2 pm/day, focally). Bone fluoride content was not increased (0.08%, N < 0.10%). All biochemical parameters of bone metabolism, including serum osteocalcin, PTH, calcidiol, calcitriol, and renal tubular reabsorption of calcium or phosphate were normal.