RADIATION OSTEITIS

Martin W. Rauch, M.D.

January 23, 1990

Case Presentation:

A 64 year-old female presented with new onset slowly worsening left chest pain 12 years after left mastectomy and radiation therapy for breast carcinoma.

Findings:

RADIOLOGY: A chest X-ray shows a diffuse mottled appearance to bones of left shoulder girdle with areas of osteopenia intermixed with sclerotic regions. There are mid-thoracic lateral rib fractures with reparative bone (arrow). Stigmata of breast cancer surgery and osseous changes confined to a typical breast cancer radiation treatment field.

SCINTIGRAPHY: Bone scintigraphy with Tc-99m MDP shows moderate focal increased uptake at the site of rib fractures. There is normal or very mild diffuse increased activity in the remainder of shoulder girdle. The exam is not significantly different from a prior bone scan 18 months earlier.

DIAGNOSIS: Osteoradionecrosis of the left shoulder girdle with lateral rib insufficiency fractures, probably with non-union. No evidence of metastatic recurrence.

Discussion:

Radiation therapy may effect bone growth, cause osteonecrosis, and induce neoplasia. Radiation changes are dose related. The larger the dose, the greater the effect and the more likely that irreversible changes will result. The threshold for changes in bone is believed to be 3000 cGy with irreversible cell death at 5000 cGy. Very acute changes are attributed to direct cytotoxic damage from radiation. Long term changes are attributed to disruption of the osseous vascular supply.

Shoulder girdle radiation changes following radiation therapy for breast cancer have been reported with an incidence of 1-7 percent. The incidence is probably lower with improved delivery of treatment. Osteopenia can occur with mastectomy alone. The coarse, disorganized sclerotic appearance may superficially resemble Paget's. Insufficiency rib and clavicle fractures are common and are typically asymptomatic often with progression to incomplete union as the fragments are no longer immobilized. Radiation necrosis of the humeral head is almost always symptomatic. The latency of these changes is long, usually 2-10 years. Scintigraphic appearance with bone seeking agents should be similar to osteonecrosis from other causes, cold early on reflecting ischemia and hot during the reparative phase.

In childhood (i.e., still actively growing bone), radiation treatment can produce epiphyseal plate closure with growth retardation, bones that are hypoplastic, and scoliosis. Osteoradionecrosis, especially when severe, may be complicated by osteomyelitis. Neoplasms following radiation therapy include benign osteochrondromas which are seen exclusively in young children. Malignant transformation usually has a very long latency period, from 4-40 years, with an average of 11 years. Fifty percent are seen in a region of radiation osteitis, and include osteosarcoma, fibrosarcoma, chondrosarcoma and malignant fibrous histiocytoma.

Differentiating radiation changes from osseous metastatic recurrence can be difficult at times. MRI may be helpful in certain cases. Marrow space fibrosis presents as low signal intensity on all sequences while tumor produces high signal on T2-weighted images.

References:

1. Resnick D, Niwayama G. Diagnosis of bone and joint disorders. 2nd Ed. Philadelphia: WB Saunders, 1988.

2. Dey H, Spencer R. Asymmetrical humeral head activity after therapeutic irradiation. Clin Nucl Med 1988; 13:681.

3. Datz F, Manaster B. Case report 391. Skeletal Radiology 1986; 15:566.

________________________________________________________

J. Anthony Parker, MD PhD, jap@nucmed.bih.harvard.edu