The diagnosis for what’s causing this patient’s persistent right leg pain is:

a) Paget’s disease of distal tibia

Originally described by British surgeon Sir James Paget in 1877, Paget’s disease of bone, also known as “osteitis deformans,” is considered the second most common bone disease of the elderly, after osteoporosis. It affects 3-5% of the population over age 40, is rarely seen under that age, and affects men more often than women. Paget’s disease is a chronic metabolic disease of bone, of unknown etiology although many have postulated viral and genetic origins. The disease results in excessive and abnormal remodelling of bone in three distinct phases: a lytic phase (often missed on plain x-rays), a mixed phase of lysis and sclerosis, and an osteoblastic phase producing sclerosis, trabecular accentuation and thickening of bone. Despite the fact that the bone is thicker and denser, it’s actually weaker than normal bone and more susceptible to fracture. Frequent sites of involvement include the skull (about 50% of cases), spine, pelvis and proximal long bones. When long bones are involved, the disease process starts at the metaphysis and moves away from the joint line, often with a flame-shaped defect as seen in the case presented. Bone scans typically demonstrate marked increased uptake of radionuclide in all phases of Paget’s disease.

Paget’s disease is often asymptomatic. The most common presenting symptoms are bone pain, fractures, bone deformity and hearing loss (calvarial disease). Sarcomatous transformation of pagetoid bone occurs in 1-2% of patients. Effective medical therapy is available in the form of salmon calcitonin (nasal administration) and new third generation bisphosphonates. Treatment can in fact reverse the course of the disease, and therefore an aggressive approach to diagnosis and treatment is advised.

Paget’s disease of bone is not related to Paget’s disease of the nipple, which is an uncommon form of breast cancer, and presents like eczema of the nipple and surrounding skin but can be fatal. It was Sir James Paget who also described this breast disease, in 1874.

Of the other choices provided, a metastatic focus from her known prior malignancy is a good possibility, but a solitary elongated met in a distal long bone would be exceedingly rare. Arthritis of the ankle would produce increased uptake on both sides of the ankle joint, not just in the distal tibia. The patient had no symptoms or risks to consider osteomyelitis. Tibial stress fracture is also a reasonable consideration, except that they typically occur in the proximal shafts of the tibiae, not the distal end, so that choice would be less likely.

References:

1. Sabourin SM et al. Am J Roengtenol 2008;191:S28-30.
2. Whyte MP. Paget’s Disease of Bone NEJM 2006;355(6):593-600.
3. Smith SE et al. RadioGraphics 2002;22:1191-216.
4. Richards PS et al. Am J Roengtenol 2001;176:816-7.
5. Ankrom MA, Shapiro JR. J Am Geriatr Soc 1998;46:1025-33