Pigmented Villonodular Synovitis: Symptoms & Treatments

Pigmented villonodular synovitis, or PVNS, is a rare condition involving the overgrowth of the synovium, a thin tissue lining the joints. The primary function of the synovium is to produce a small amount of fluid that lubricates the joint, allowing for smooth movement. In PVNS, this lining thickens and grows excessively, forming a benign mass.

This overgrowth can be locally aggressive, meaning it can invade and damage surrounding tissues and bone, even though it does not spread to distant parts of the body. The condition is considered a type of tenosynovial giant cell tumor. While it can affect individuals of any age, it is most commonly diagnosed in adults between the ages of 20 and 50.

Forms and Symptoms of PVNS

Pigmented villonodular synovitis presents in two distinct forms: localized and diffuse. The localized, or nodular, type is characterized by a single, well-defined growth within the joint. In contrast, the diffuse form involves the entire synovial lining of the joint, leading to more widespread effects and a more challenging clinical picture.

The onset of symptoms is often gradual and can fluctuate over time. Patients experience swelling in the affected joint, accompanied by persistent pain and stiffness. A feeling of the joint locking, catching, or giving way is also a common complaint, interfering with normal movement.

While any joint can be affected, PVNS has a strong predilection for the knee, accounting for up to 80% of cases. Following the knee, the most frequently involved joints are the hip, ankle, shoulder, and elbow. The condition almost always affects only a single joint.

The Diagnostic Process

Diagnosing PVNS begins with a thorough physical examination. A physician will assess the affected joint for swelling, tenderness, and any limitations in its range of motion. Because the symptoms of PVNS can mimic more common conditions like arthritis, this initial assessment is a starting point for a more detailed investigation.

Imaging studies are a component of the diagnostic process. Magnetic resonance imaging (MRI) is the most effective tool, providing detailed pictures of the joint’s soft tissues. An MRI can clearly show the thickened, overgrown synovial lining and help determine the extent of the condition, distinguishing between the localized and diffuse forms. X-rays may also be ordered to evaluate if the overgrowth has caused any erosion or damage to the adjacent bone.

While imaging provides strong evidence, the definitive diagnosis is made through a biopsy. A small sample of the abnormal synovial tissue is surgically removed from the joint. This tissue is then examined under a microscope by a pathologist. The presence of specific cells, including hemosiderin-laden macrophages which give the tissue a brownish color, confirms the diagnosis of PVNS.

Medical Interventions

The primary treatment for PVNS is surgery to remove the abnormal synovial lining, a procedure known as a synovectomy. The surgical approach depends on the form and extent of the disease. For localized PVNS, surgeons often perform an arthroscopic synovectomy, using small incisions and specialized instruments to remove the single mass. For the more extensive diffuse form, an open synovectomy, which involves a larger incision, may be necessary to ensure all affected tissue is removed.

When PVNS is particularly aggressive, recurs after surgery, or is in a location that makes surgery difficult, other treatments may be considered. External beam radiation therapy uses high-energy rays to target and destroy the abnormal cells. This is used as an adjunct to surgery to help reduce the high rate of recurrence associated with the diffuse type.

A more recent development in treatment is the use of systemic targeted therapy. Pexidartinib is an FDA-approved oral medication specifically for patients with symptomatic PVNS where surgery is not a viable option. This drug works by blocking the activity of a protein called colony-stimulating factor 1 receptor (CSF-1R), which is involved in the abnormal cell growth seen in PVNS.

Recurrence and Post-Treatment Management

A defining characteristic of PVNS is its tendency to return after initial treatment. The rate of recurrence is notably high, particularly for the diffuse form of the disease, even after a seemingly successful synovectomy. This makes long-term monitoring an important part of patient care.

Following treatment, patients enter a phase of active surveillance. This involves regular follow-up appointments with their orthopedic specialist. Surveillance MRIs are performed at scheduled intervals to monitor the joint for any signs of returning disease. Early detection of a recurrence allows for prompt intervention, which may involve further surgery or other therapies.

Over time, the damage caused by PVNS can lead to secondary conditions. Some patients may develop osteoarthritis in the affected joint due to the erosion of cartilage and bone. Management of these long-term effects, such as joint pain and stiffness from arthritis, becomes an ongoing part of the patient’s care plan.

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