Pigmented Villonodular Synovitis (PVNS) is a rare, benign joint disorder characterized by the overgrowth of the synovium, the soft tissue lining that lubricates and protects the joint. Although locally aggressive, meaning it can severely damage the joint it affects, it rarely spreads to other parts of the body. PVNS most frequently occurs in large joints, primarily the knee (up to 80% of cases), followed by the hip, ankle, and shoulder. It typically affects young to middle-aged adults, often leading to a challenging diagnosis because initial symptoms mimic more common joint problems.
Defining Pigmented Villonodular Synovitis
The pathology of PVNS involves a proliferative process where synovial membrane cells multiply uncontrollably, forming thickened, often nodular tissue within the joint space. The characteristic “pigmented” appearance is due to large deposits of hemosiderin, an iron-storage complex derived from chronic, low-grade bleeding within the joint.
This cellular overgrowth is not caused by trauma or infection, and while the exact cause remains unknown, some research suggests a link to genetic factors. PVNS is classified into two forms: localized and diffuse. The localized form presents as a single, well-defined nodule, while the diffuse form involves the entire joint lining and is more aggressive and difficult to manage.
Recognizing the Symptoms
Symptoms of PVNS often develop slowly, which frequently delays diagnosis for years. Patients typically experience a gradual onset of persistent swelling in the affected joint, often disproportionate to the level of pain. This swelling is caused by joint effusion, an excessive accumulation of joint fluid.
The pain is commonly described as a dull or aching sensation and may be poorly localized. Stiffness and a limited range of motion are also common complaints. In the localized form, mechanical symptoms such as joint locking, catching, or giving way are often the predominant concern.
Aspiration of the joint fluid can sometimes yield a characteristic brownish or blood-tinged fluid (hemarthrosis), which results from the hemosiderin-laden tissue. In advanced diffuse cases, the chronic disease can lead to secondary degenerative changes and cartilage destruction.
Confirming the Diagnosis
The diagnostic process begins with a physical examination and imaging studies, as routine blood tests for inflammation are usually normal. X-rays are often non-specific in the early stages, typically showing only joint effusion. In advanced diffuse cases, however, X-rays may reveal bone erosions on both sides of the joint.
Magnetic Resonance Imaging (MRI) is the most effective imaging tool for identifying PVNS, as it clearly visualizes the proliferative soft tissue mass. The hemosiderin deposits produce a distinct signal on MRI scans, appearing as areas of very low signal intensity on both T1- and T2-weighted images.
A definitive diagnosis requires a tissue sample, or biopsy, obtained either through a needle procedure or during surgery. Pathological analysis confirms the presence of proliferating synovial cells, multinucleated giant cells, and hemosiderin-stained macrophages. This microscopic confirmation is necessary to distinguish PVNS from other joint conditions.
Management and Treatment Options
Treatment for PVNS is primarily surgical, involving the complete removal of the diseased synovial tissue, a procedure known as synovectomy. This intervention aims to stop destructive proliferation and relieve symptoms. The approach can be arthroscopic (using small incisions and a camera) or open (involving a larger incision for better visualization).
Surgical Approaches
For the localized form, arthroscopic synovectomy is often successful because the mass is well-contained. Treating the diffuse form is challenging because complete removal of the widespread, infiltrated synovium is technically difficult. In these cases, an aggressive open synovectomy, sometimes combined with an arthroscopic approach, is often required to reach all affected areas.
Adjuvant Therapy and Recurrence
Despite surgical effort, the diffuse form of PVNS has a high recurrence rate, potentially 50% or more with surgery alone. To address this risk, adjuvant therapy is frequently used, particularly for diffuse disease. External beam radiation therapy (EBRT) is a common post-operative treatment, often delivered at doses around 20 to 36 Gray (Gy).
Radiation destroys any remaining microscopic disease that surgery could not eliminate and significantly reduces the recurrence rate. Alternatively, intra-articular radiation, known as radiosynoviorthesis, involves injecting a radioactive substance directly into the joint space to target residual tissue. The choice of adjuvant therapy depends on the extent of the disease and the patient’s overall health.
Targeted Medical Therapies
In cases of advanced, recurrent, or surgically inaccessible disease, newer targeted medical therapies are being investigated. These systemic treatments focus on specific molecular pathways that drive the disease, such as inhibitors targeting the colony-stimulating factor one receptor (CSF1R). These medications offer a non-surgical option for managing challenging instances of PVNS.