BENIGN AND MORE SEVERE FORMS

One of the most significant points to remember is that the disease comes in a wide variety of clinical forms. Many patients “have FD and don’t know it”. These are, in general, monostotic forms, discovered by accident following an X-ray for another reason. If the lesion is small or is not on a weight bearing bone, then there will be no orthopaedic complications, or pain and will only be discovered with an X-ray.

On the other hand, when there are many bones affected, with frequent fractures and skeletal deformities, physical disability can be severe. All eventualities, between asymptomatic cases and those with multiple fractures and deformities, are possible. Physical disability therefore varies greatly from person to person.

The disease can present itself through a spontaneous fracture or following a slight knock. Deformities occur as a result of these fractures, or form progressively. They are only visible in bones beneath the skin. Bone pain is linked to cracks and fractures, but can also occur spontaneously and can develop of its own accord. Sometimes these pains accompany signs of localised inflammation, with localised residual heat felt in bones located beneath the skin (the tibia for example).

When many bones are affected, the disease is found in bones located in one side of the body (affect said to be hemimelic). The bones most commonly affected are those of the lower limbs, the pelvis, the ribs, the skull and the face. The upper limbs are rarely affected, with the spinal column even less commonly so.

THERE ARE NOT JUST BONE ABNORMALITIES

It is often noted, in people with a polyostotic form, that blood phosphorous levels are too low. This relates to its excretion into the urine. This phosphate diabetes is caused by the over production of the phosphorus regulating protein (FGF-23) in the diseased bone cells. A phosphorous deficiency can lead to a mineralisation defect (deposit of calcium and phosphorous in the bone) within the dysplasic bone, and may also affect nearby healthy bone. Warning: when phosphorous diabetes is mentioned, this has nothing to do with diabetes mellitus; this is signified only by the excretion of phosphorus in the urine. In cranio-facial forms, expansion of the bone can reduce the diameter of the optic canals and compress the optic nerves, and also push on the eyeball, making it partially protrude from the orbit (this is what is called exophthalmia). Compression of the optic nerves can lead to blindness. This complication is rare (90% of patients will never have this problem), however it warrants regular ophthalmological monitoring (with studies of visual field and eye fundus) to catch any change in vision early and thus plans for decompression surgery can be made before irreversible complications appear.

An endocrine problem

Created: 09 june 2010