AP radiograph of right hip
AP radiograph of right hip
Click the image for a more detailed view.
This image demonstrates markedly prominent trabeculae in the right femoral head, neck and proximal shaft. Why are they prominent? Well, usually when one see prominent trabeculae, there are two possibilities -- either all of the other trabeculae have been resorbed or the trabeculae have actually gotten bigger.
The first phenomenon is seen in patients with osteoporosis, in which the trabeculae that do the most work are the last to be resorbed. In the spine, this means that the vertical trabeculae, which resist most of the axial loading forces of the spine, will be the last to go. In the proximal femur, the primary compressive group of trabaculae will be the last to go. However, since the pelvic and left femoral trabeculae are normal in size, this is not what is going on in our patient.
The second phenomenon is seen in patients with Paget's disease. In the spine, prominent vertical trabeculae can also be seen in hemangiomas of the vertebral body. If one looks closely, one can see a zone of transition in the right femoral shaft, below which is normal bone and above which there are prominent trabeculae. This represents the so-called "blade of grass" sign of Paget's disease. This is merely a reflection of the fact that Paget's disease almost always begins at one end of a bone and then propagates down that bone until the entire bone is involved. Why does it do this? No one knows.
No one really knows what the real cause of Paget's disease is, but the smart money is on a slow viral infection, since one can see virus-like bodies in the osteoclasts on electron micrography in these patients. Which virus? This is unknown, although these viral bodies are morphologically similar to those of measles virus or respiratory syncytial virus.
Paget's disease can be divided into 3 major phases: 1) lytic ; 2) mixed lytic-sclerotic; and 3) sclerotic phases. The first phase is characterized radiographically by an advancing wedge of osseous rarefaction and pathologically by markedly increased osteoclastic resorption. In the second phase, one sees both osteoclastic and osteoblastic hyperplasia pathologically, which leads to boney enlargement, which is expressed as boney widening, trabecular coarsening, cortical thickening, and other sclerotic areas. In the third phase, the bones continue to widen, and become weakened due to defective bone production. Pagetic bone can lead to pathological fractures, bowing deformities, and a variety of neurological complications. Some investigators would add a 4th phase to Paget's disease: malignant degeneration into a sarcoma.
Paget's is most common among subjects of European descent (the prevalence is about 3% in this group). It is much less common in patients of Asian or African descent. Over 90 % of patients are over 40 years old, although there are also juvenile and infantile forms of Paget's disease. Paget's disease occurs about 1.5 times more commonly in men than women, and some studies have shown a familial tendency to the disorder.
Why did this patient complain of left hip pain? We don't know. Paget's disease can be asymptomatic in up to 90 % of cases, so one shouldn't be too surprised that this patient had no symptoms in the involved right hip. Isn't it unfair to present a case with a red herring like this? I would say no, since that's how this patient actually presented. Real life is often unfair, and one must just learn to deal with it.
Since Paget's is commonly clinically silent, it is often first diagnosed on radiographic or scintigraphic studies performed for some other reason. Paget's disease causes intense uptake in involved bones on bone scans.
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