Skeletal fluorosis is a chronic metabolic bone disease caused by the ingestion of large amounts of fluoride.

Clinical presentation

While often asymptomatic, non-specific signs and symptoms may be present, including ⁸:

• bone and joint pains

• kyphosis

• radiculomyelopathy

• dental fluorosis, with characteristic mottling of dental enamel

Pathology

Large amounts of fluoride may be ingested through either water or food in geographic areas where high levels of fluoride occur naturally. Xenobiotics associated with fluorosis include fluorinated hydrocarbons ⁹ (e.g. difluoroethane), sodium-aluminium fluoride (also known as cryolite), sulfuryl fluoride ¹⁰, and voriconazole, the latter of which may be associated with a diffuse asymmetric periostitis secondary to elevated fluoride levels ⁷. Regardless of the cause, fluoride forms fluorapatite, which stimulates osteoblastic activity and periostitis ⁷.

Radiographic features

Plain radiograph/CT

Described features include:

• increased bone density: osteosclerosis

• osteopenia or osteoporosis (less common), especially in younger patients at an earlier stage ^4,6

• trabecular blurring or haziness

• compact bone thickening

• periosteal bone formation

• ossification of the attachments of tendons, ligaments, and muscles

• interosseous membrane calcification ¹

• ossification of the posterior longitudinal ligament ²

In early fluorosis, the first changes are bone deposition and thickening at the junctions of trabeculae. This is seen as a sand-like, granular, or particle-like bone structure on radiographs. In more advanced fluorosis, the trabeculae are more generally thickened because of new bone formation on the trabecular surface. At this stage, radiographs show thickening and condensation of trabeculae, with coarse reticulum or woven bone striations. If the trabeculae are fused, focal round densities are seen in the medullary bone.

Involvement of the axial skeleton is characteristic, and changes are most marked in the spine, pelvis, and ribs. Calcification of the sacrotuberous ligament is considered another characteristic feature.

Treatment and prognosis

No specific treatment is available, and treatment is thus symptomatic ⁸.

Differential diagnosis

For diffuse skeletal sclerosis on imaging, consider:

• diffuse bony sclerosis mnemonic