Osteomalacia

Radiological markers and deformities

Specific bone changes form the basis of diagnosis. The most telling sign is Looser's zones. These are unmineralized areas appearing as radiolucent bands running perpendicular to the cortical bone. MRI or radionuclide scintigraphy is used to detect occult zones.

Bone softening leads to characteristic skeletal deformities:

• Pelvis and hip: The femoral head is pressed into the acetabulum (protrusio acetabuli), with the normal contour of the teardrop figure disappearing. If vitamin D deficiency persists since childhood, the pelvis acquires a triradiate shape.
• Tubular bones: Curvature develops (genu varum or genu valgum).
• Spine: Intervertebral discs herniate into the softened vertebral bodies, making them biconcave («fish vertebrae» deformity).

Differential diagnosis

It is important to differentiate true Looser's zones from other pathologies with a similar radiological presentation:

• Insufficiency fractures: Occur against the background of osteoporosis in fragile bones. Unlike osteomalacia, these microfractures are accompanied by abundant callus formation.
• Paget's disease: Incremental microfractures appear on the convex side of the cortical layer. In classic osteomalacia, Looser's zones are located medially — on the concave surface of the bone.

X-linked hypophosphatemia (XLH)

This is the most common form of genetically determined rickets, resulting from lifelong renal phosphate wasting. The initial clinical manifestations become noticeable in children aged 6–12 months.

Features of the clinical and radiological picture of XLH:

• Paradoxical osteosclerosis: Despite the mineralization defect, bone density is increased on X-ray, and a coarse trabecular pattern is visualized.
• Atypical Looser's zones: Unlike nutritional osteomalacia, they are more frequently located on the outer cortical layer of the bowed femur and persist for a long time even after treatment, filling with fibrous tissue.
• Enthesopathies: Ossification of tendons develops. In the spine, this process can lead to complete ankylosis mimicking ankylosing spondylitis (however, the sacroiliac joints remain unaffected).
• Deafness: Sclerosis of the petrous part of the temporal bone leads to hydropic cochlear sensorineural hearing loss.
• Spinal cord compression: A rare but formidable complication caused by ossification of the yellow ligament (ligamentum flavum).

Renal lesions and bone metabolism

Kidney diseases lead to osteomalacia through two main scenarios:

1. Renal osteodystrophy: Develops in chronic kidney disease (CKD). Decreased calcium levels trigger secondary hyperparathyroidism, manifesting as subperiosteal bone resorption (e.g., the "pepper-pot skull" sign on the skull vault). Dialysis patients frequently exhibit calciphylaxis, a severe metastatic soft tissue calcification.
2. Renal tubular defects: Impaired reabsorption of phosphates, glucose, and amino acids. These can be congenital (Fanconi syndrome) or acquired (exposure to heavy metals, drugs, Wilson's disease). An important distinction: serum calcium levels remain normal, therefore secondary hyperparathyroidism does not develop.

Class and exam questions

What else to study on this topic

• Secondary hyperparathyroidism: pathogenesis and subperiosteal bone resorption.
• Calciphylaxis in chronic kidney disease.
• Oncogenic osteomalacia and the role of FGF-23.
• Hypophosphatasia: mechanisms of development and inheritance patterns.
• Diagnosis of tubular dysfunctions (Fanconi syndrome).

Other topics in the "Musculoskeletal System" section

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