What is fibrous dysplasia?
Fibrous dysplasia is a congenital bone condition characterized by replacing normal bone by a more fragile fibrous tissue. The lesions usually appear in childhood. Any bone can be affected, but the most affected bones are the ribs, femur, and bones of the skull. It results in bone fragility and deformities. All bones can be affected, however the disease most commonly affects the femur (thigh bone), tibia (leg bone), ribs and skull bones. It can cause pain in the affected bone (s), increases the risk of fractures and leads to bone deformities. When the bones of the skull are affected, neurological complications can arise. More exceptionally, hormonal complications appear.
Fibrous dysplasia is a rare disease, the number of cases of which in the population is not precisely known. Indeed, the disease is frequently asymptomatic, so many patients ignore their disease. It affects both girls and boys, from all geographic origins. Patients are between 5 and 30 years old when diagnosed.
This pathology is of genetic origin, and more precisely, caused by the abnormality of the GNAS gene. This gene corresponds to a code which makes it possible to produce a protein. Proteins have extremely varied functions, they contribute to the proper functioning of cells and therefore of the organism as a whole. In fibrous dysplasia, the GNAS protein is changed in some bones. The bone is gradually replaced by fibers. The bones are then larger and above all more fragile.
Symptoms of fibrous dysplasia depend on the location of the bone abnormality and the number of bones involved. The disease can indeed affect a single bone (monostotic) as well as several (polyostotic).
The monostotic form represents 70 to 80% of cases. The most commonly affected bones are the ribs, femur, tibia, skull bones, or jaw. The pelvis, vertebrae and bones of the arm are sometimes affected.
The polyostotic form is more severe, and mainly concerns the femur (90% of cases), the tibia (80% of cases), the pelvis (80%) with the ribs, the bones of the skull, the arms and The vertebrates. Several bones can be affected in a single limb, on both sides of the body, or on one side of the body.
Fibrous dysplasia is present from birth, but may not appear until much later, especially when it affects only one bone.
Damage to the bones is usually seen in childhood, and may get worse with growth. The most common symptoms are:
- Bone pain is more or less sharp. They are generally located at the level of the femur or the tibia, and are deaf, continuous with a feeling of support on the limb. The intensity of the pain varies from mild to severe. The painful area may be swollen;
- Bone deformation (increase in volume, asymmetry). When the disease manifests during growth, one or more bones can develop abnormally and lead to asymmetry. Spinal damage can lead to a deformity of the spine ( scoliosis ). Also fractures can cause deformations and weaken the bone even more;
- Difficulty performing certain movements or lameness.
When the bones of the face (jaw, cheekbones) and the skull are affected, we speak of craniofacial form. The aesthetic damage can be significant. This type of attack affects 10 to 25% of patients with the monostotic form and up to 50% of patients with the polyostotic form. Indeed, bumps can appear on the forehead, the skull or the cheekbones resulting in an asymmetrical deformation, sometimes very marked. Headaches are also often associated, they are manifested by seizures. The eyes can be affected, and visual disturbances occur (reduced visual acuity and poor visibility to the sides). Finally, hearing problems, loss of smell and tooth implantation problems can occur in connection with the deformation of the bones of the skull.
In half of the cases, the entire skeleton is weakened, because the phosphorus which normally ensures the solidity and rigidity of the bones is insufficient.
Other manifestations can be associated:
- Cutaneous. Almost half of individuals with the disease also have one or more more or less dark spots on the skin;
- In less than 5% of cases, the hormonal system is also disturbed. Puberty occurs abnormally early, usually before the age of 10. It can be associated with an acceleration of the growth which can occur only on one side of the body and thus be at the origin of important deformations. Thyroid hormones can also be disrupted resulting in nervousness, sleep disturbances, fatigue and weight loss.
Very rarely, the disease is accompanied by the presence of benign tumors called intramuscular myxomas that do not cause any symptoms.
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When fibrous dysplasia does not cause symptoms, it is discovered incidentally during an x-ray.
If symptoms occur, such as pain, lameness, or a fracture, diagnosis requires an x-ray (or CT scan) to visualize the abnormal appearance of the bone. When in doubt, a biopsy (sample of tissue to be analyzed under a microscope) may be prescribed.
There is no cure for fibrous dysplasia. Management is symptomatic, that is to say, involves relieving symptoms such as pain, and preventing complications such as fractures.
Bone pain is generally difficult to alleviate with conventional analgesics (paracetamol, ibuprofen, etc.). Opioids can be prescribed. Another class of drugs, called bisphosphonates, can be used to limit bone damage and therefore pain. These drugs are given intravenously every 6 months for several years. If the treatment is effective, the treatments can be spaced out. Calcium and vitamin D supplementation may be prescribed in addition to increasing the effect of bisphosphonates.
Regular physiotherapy sessions are recommended to maintain sufficient musculature and limit bad postures.
In half of the patients, the phosphate is present in too small an amount because of its excessive elimination in the urine. Phosphorus supplementation is then offered.
Fractures or deformities require surgical treatment. Often, osteosynthesis (fixation of the broken bone by screws, rods or metal plates) is performed. Sometimes, when the risk of fracture is very high, the bone is consolidated with rods or plates for prevention. Preventive bone grafts can also be offered.
Regarding bone deformities, an osteotomy can be performed. This procedure consists of straightening the deformed bone by cutting a part to correct the curvature.