Pigmented nodular synovitis
by Nathan Wei, MD, FACP, FACR
Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.
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From the American Academy of Orthopedic Surgeons and emedicine
Pigmented villonodular synovitis is an uncommon disease and the diagnosis is not easy to make.
There are two forms of the disease: a localized type characterized by an isolated polyp-like lesion and a type with diffuse joint involvement.
The etiology of pigmented villonodular synovitis is controversial. The most common theory is that the disease is an inflammatory reaction of the synovium: however, some evidence suggests it is a benign neoplastic process.
The incidence of pigmented villonodular synovitis is 1.8 cases per 1 million people per year Most studies show the disease to be equal between males and females. Pigmented villonodular synovitis (PVNS) generally occurs in patients between the ages of 20 and 45 years.
The majority of patients with pigmented villonodular synovitis have monoarticular complaints of pain and swelling. In both the localized and diffuse subtypes, the knee is the most commonly affected joint (about 80 percent of patients), followed by the hip, ankle, small joints of the hands and feet, shoulder and elbow.
PVNS is a proliferative synovitis with brownish villonodular fronds in the affected joints. Diffuse disease is characterized by a mononuclear cell infiltrate in the synovial membrane. Hemosiderin-laden macrophages give the brown color. Other cell populations include foam cells and multinucleated giant cells.
Diffuse pigmented villonodular synovitis of the knee can look like many other conditions. The disease is also confused with inflammatory arthritis, ligament instability and other conditions.
Patients with diffuse pigmented villonodular synovitis of the knee complain of the slow progression of symptoms. Only one third of these patients report previous trauma to the knee. Patients also tend to complain of intermittent swelling and stiffness around the joint. The diagnosis of diffuse pigmented villonodular synovitis may be suggested by a clinical history of swelling that has an vague onset, is not preceded by trauma, and is out of proportion to the degree of discomfort.
On physical examination, up to 96 percent of patients have swelling of the knee and a large effusion. About 40 percent of patients have a palpable mass. Up to 90 percent of patients complain of mild to moderate tenderness, mainly over the medial knee. Joint fluid is blood-tinged in 44 to 69 percent of patients.
In patients with pigmented villonodular synovitis of the knee, plain x-rays are usually normal. In general, bone and joint changes are less common in the knee than in the hip, because the knee capsule expands to accommodate the hyperplastic synovium.
In patients with diffuse pigmented villonodular synovitis of the knee, magnetic resonance imaging may show a large effusion, low signal intensity on both T1- and T2-weighted images (because of hemosiderin deposition), synovitis, and occasional bony erosions.
The hip is the second most common location for pigmented villonodular synovitis. Like patients with knee disease, those with hip disease usually present with deep monoarticular pain of variable duration. The pain is often made better with rest. Patients may localize the pain to the groin or the lateral part of the hip. The pain is intermittent.
Patients occasionally report episodes of extreme pain, which may represent hemorrhage into the joint space.
Patients may also report decreased range of motion. In pigmented villonodular synovitis of the hip, x-rays show bony erosions in the head and neck of the femur and acetabulum in 95 percent of patients. These erosions are found early in the course of disease and appear cyst-like.
Erosions are much more common in the hip than the knee, primarily because the tight capsule of the hip joint does not allow the joint to expand to accommodate the enlarged and inflamed synovium. As a result, intracapsular pressure increases, and bone erosion occurs.
MRI is highly sensitive and specific for the diagnosis of pigmented villonodular synovitis of the hip. Characteristic MRI findings include hip joint effusion, lifting of the joint capsule, low signal intensity on both T1- and T2-weighted images (because of hemosiderin deposition), hyperplastic synovium, and bony erosions.
Pigmented villonodular synovitis should be considered in the differential diagnosis of patients aged 20 to 45 years who have monoarticular symptoms. Most patients with this disease have a long history of pain and disability. The presence of non-traumatic effusions of the hip or knee is suspicious.
Patients with nontraumatic knee effusions should undergo arthrocentesis. The finding of blood-tinged fluid is highly suggestive. MRI should be performed to define the extent of the disease. The same is true for the hip.
The diagnosis of pigmented villonodular synovitis is confirmed by biopsy of the synovium. The treatment of choice is synovectomy. Associated bony lesions should be carefully curettaged, and bone grafting should be performed as necessary.
Diffuse pigmented villonodular synovitis has a high rate of local recurrence. The role of radiation therapy in the management of refractory disease is not clear.
Synovectomy may not relieve all symptoms in patients with significant destructive changes in the joint. Total joint replacement should be considered.
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