Fibrous dysplasia is a rare bone disorder in which the normal bone is replaced by fibrous tissue. Read this article to know more about its causes, symptoms, types, and treatment.
Dysplasia refers to the abnormal development in cells within a tissue or organ. It is not itself cancer, but it may progress and develop as cancer. It can occur in any body area, and it can lead to severe abnormalities based on the rate of dysplastic changes occurring in the body. It can be mild, moderate, and severe, depending on the varying degree of severity.
Fibrous dysplasia refers to a chronic condition in which the abnormal fibrous connective tissue grows in place of normal bone. The abnormal fibrous connective tissue weakens the bone making it more brittle and prone to fracture. It was first described by Dr. Lichtenstein and Dr. Jaffe in 1942. It was originally termed Jaffe - Lichtenstein syndrome. It affects any bone; some of the most commonly affected bones include the following:
Skull bones (including the facial bones).
Upper arm bone (humerus).
Pelvis (hip bone).
The femur (thigh bone).
Tibia (shin bone).
Vertebrae in the spinal cord.
It is the most common region affected by FD as well as difficult to manage. It leads to many dental problems like jaw swellings, misaligned teeth, etc. FD involving jaw bones affect the maxilla (upper jaw bone) twice that of the mandible (lower jawbones).
The types of fibrous dysplasia include:
Monostotic Fibrous Dysplasia: It is the most common form of fibrous dysplasia. Only a single bone is affected. Mostly the patients are asymptomatic or experience less severe symptoms in this form of FD.
Polyostotic Fibrous Dysplasia: Two or more bones are affected in this condition. This form is more severe than the monostotic form of fibrous dysplasia.
McCune-Albright syndrome can be described as a triad of
Cafe-au-lait spots (pigmented spots of skin).
Polyostotic fibrous dysplasia of bones.
Endocrine dysfunction with precocious puberty (early puberty).
It is caused by mutations in the GNAS1 gene. It is more frequently found in girls. The cause of precocious puberty is due to autonomous production of estrogen by the ovaries. MAS-affected individuals exhibit some endocrine abnormalities like hyperthyroidism, Cushing syndrome (excess cortisol production seen), and excess growth hormone production by the pituitary gland.
The exact cause of fibrous dysplasia is unknown. But it is believed by many researchers that mutation in the GNAS1 gene causes this condition. Since this mutation occurs after embryo fertilization (somatic mutation), this condition is considered neither inherited nor the affected individual can transmit the mutation to their children. The reasons why somatic mutations occur are still unknown. The GNAS1 gene mutation leading to improper differentiation of osteoblasts (bone-forming cells) contributes to the development of FD.
FD is more prevalent among children starting from ages three to 15. Since it is a chronic disorder sometimes may go undiagnosed until adulthood. Equal predilection among males and females is seen. The monostotic form of FD affects nearly 80% of the cases.
FD rarely tends to develop into a cancerous condition which is less than 1% of prevalence; this demonstrates the condition as benign mostly. The malignant transformation of FD shows warning signs like severe pain at the affected site, enlarged swellings, and rapid growth of the lesion. On the other side, mild or benign cases of FD exhibit no signs or symptoms at all, but in other cases, the symptoms include the following:
Pain and tenderness in the affected area.
Weak and brittle bones.
Misshapen bones due to bone deformity.
Slight injuries over the affected area resulting in bone fractures.
Endocrine disorders such as excessive growth hormone production, hyperthyroidism, and precocious puberty are seen.
FD Affecting the Craniofacial Region Shows the Following Symptoms:
Severe pain in the affected area.
Misaligned or displaced teeth.
Compression of specific nerves in the craniofacial region results in vision and hearing loss.
Diagnosis of FD is made based on the symptoms, patient history, clinical findings, imaging tests, biopsy, and various other specialized tests. Let us see the various diagnostic tools used in diagnosing FD.
1. Imaging Tests:
X-Ray: X-ray plays a major role in diagnosing FD as it detects all the abnormalities of the bone. It helps in diagnosing the undiagnosed mild cases of FD as patients have been asymptomatic for years. It gives a clear picture of the number of bones affected, the site of the lesion, and the extent of involvement. It differentiates between monostotic and polyostotic fibrous dysplasia; thus, it helps in planning proper treatment for the disease.
Specialized Imaging Tests: Specialized imaging tests like MRI (magnetic resonance imaging) and CT (computed tomography) are used in FD diagnosis.
2. CT Scan: It is a much superior radiographic approach as it delineates the morphological changes in bone. It defines the anatomy as well as the extent of the lesion.
3. MRI: MRI uses magnetic fields and radio waves to produce cross-sectional images of a particular organ and tissues. It gives a clear picture of the amount of bone involved and helps in determining whether the lesion is benign or malignant.
4. Bone Scans: Bone scans (also known as bone scintigraphy) involve the use of a very small amount of radioactive dye injected into the patient's body intravenously. The abnormal cells in the affected area absorb the radioactive dye and exhibit “hot spots” through the scan. These hot spots reveal whether the lesion is cancerous or not.
5. Bone Biopsy: In a bone biopsy, a small amount of affected bone is removed by a hollow needle and is sent to pathologists for microscopic examination. This reveals the dysplastic features and provides a definitive diagnosis of the disease.
6. Lab Diagnosis: Blood tests of fibrous dysplasia reveal elevated levels of serum alkaline phosphatase, especially in the active growing phase of FD. PCR (polymerase chain reaction) along with PNA (peptide nucleic acid) determines the presence of G protein gene (GNAS) mutation in the blood cells of FD patients.
Radiographically mixed radiolucent and sclerotic lesions are often seen with expansion. The lesion appears smooth and homogenous with endosteal scalloping and cortical bone thickening. Some of the characteristic radiographic appearances of FD include,
Ground glass appearance.
Rind sign (a radiolucent lesion surrounded by a thick sclerotic border).
FD is treated by both surgical and non-surgical modes of treatment. Doctors will suggest either one or both modes by diagnosing the severity of the disease.
1. Non-Surgical Treatment:
It includes medications like bisphosphonates which prevents bone loss by decreasing the osteoclastic activity. Examples of bisphosphonate drugs include Etidronate, Pamidronate, etc. Other non-surgical treatments include bracing, which prevents the bone from fracturing. Physical therapy is also carried out.
2. Surgical Treatment:
Doctors may suggest surgical treatments if you have:
Symptomatic lesions which do not respond to non-surgical treatment.
The lesion becomes cancerous.
What Are the Differential Diagnoses of FD?
The differential diagnoses of fibrous dysplasia include:
Paget’s disease (a bone disorder in which the replacement of old bone tissue with new bone tissue is disrupted).
Neurofibromatosis type1 (an inherited condition characterized by skin pigmentation and tumor growth in nerves of the skin, brain, and other body parts).
Adamantinoma (rare malignant tumor mostly seen in the diaphyses and metaphyses of long bones).
Fibrous dysplasia is a chronic bone disorder that can affect any bones in the body. It disrupts the normal bony architecture and weakens the bone. An early diagnosis of the condition helps in treating it better. Do consult your doctor if you suspect any symptoms related to fibrous dysplasia in your body.
Last reviewed at:
22 Jun 2022 - 5 min read
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