Fibrous dysplasia of the bone (types, description)

Fibrous dysplasia (FD) of the bone is a peculiar condition that affects either all bones or a single bone in the body. Most cases are diagnosed in adolescence and young adulthood and remain unchanged throughout life. The initial manifestations of fibrous dysplasia are most commonly found in persons aged 3-15 years.
In the past, many conditions that could not be satisfactorily explained have been included under this disease. The bone in this condition is fibrous or plastic in quality and is defective in form as well.

Types

Fibrous dysplasia of the bone is divided into two types:

1· Monostotic fibrous dysplasia
2· Polystotic fibrous dysplasia

In monostotic type only one bone is involved, and hence the prognosis of this type is definitely better. In polystotic type, more than one bone or a group of bones is involved, and the prognosis is poorer. 

Monostotic Fibrous dysplasia of the bone

This condition affects mostly people in the age group 10-30. It involves excessive growth of hard fibrous tissue that replaces normal bone tissue in a single bone. Approximately 70-80% of FD cases are monostotic, occurring most frequently in the rib (28%), femur (23%), tibia, craniofacial bones (10-25%), and humerus. With monostotic disease, patients as old as 20 or 30 years are asymptomatic.

The cause of this condition is unknown although several theories have been proposed. One theory attributes this disease to abnormal activity in the bone forming tissues prior to birth. Another theory says any localized infection or trauma gives rise to this disease. In some cases, Monostotic FD of the bone has occurred as an autosomal recessive trait.

Symptoms

The first sign of the disease is a painless bulging in the affected jaw. As the lesion is constantly expanding, they could lose their balance of contacting the teeth in the opposite jaw, and as a result, there may be disturbance in the teeth as well. . When Fibrous dysplasia occurs in the upper jaw of the maxilla, Monostotic FD is a serious condition. The lesion extends into the maxillary sinus, and on the face. At times it may extend to the base of the skull and obstruct vital nerves, causing irreparable damage.

Treatment

The treatment of Monostotic FD of the bone is usually radical surgery. This surgery mutilates the entire bone involved, sometimes necessitating block resection as well. In some cases, this condition could lead to osteosarcoma or cancer of the bone.

Polyostotic fibrous dysplasia

This condition affects a number of bones in the body, mostly the long bones. About 20-30% of FD cases are polyostotic. Two thirds of patients exhibit symptoms before the age of 10. Polyostotic FD frequently involves the skull and facial bones, pelvis, spine, and shoulder girdle. The sites of involvement are the femur (91%), tibia (81%), pelvis (78%), ribs, skull and facial bones (50%), upper extremities, lumbar spine, clavicle, and cervical spine, in decreasing order of frequency.

(Polyostotic fibrous dysplasia with orbital involvement in a 15-year-old boy)

Symptoms

There is a thickening of the long bones and the patient usually complains of persistent bone pain.

Often, the initial symptom is pain in the involved limb and, spontaneous fracture, or both. Leg-length discrepancy is present to varying degrees in 70% of patients with limb involvement. The weight bearing bones become bowed due to weakening of the structural integrity of the bone.

The bones of the face and the skull are involved in a majority of the cases and sometimes are unilateral in distribution. If this happens, there is an obvious deformity of the face.

Sometimes brown lesions called the "cafe-au-lait" spots are present on the skin. Vaginal bleeding is another feature of this condition. Teeth do not erupt into the oral cavity on time. Several hormonal disturbances are also commonly seen. The thyroid, parathyroid and the pituitary as well as the ovary are involved.

Treatment

Mild cases are satisfactorily treated with surgery. But in severe cases, radiation therapy has been tried with limited success. The lesions have a high potential to turn malignant.