Working Diagnosis:
After MRI was obtained, our final working diagnosis was Pigmented Villonodular Synovitis (PVNS), also known as Tenosynovial Giant-Cell Tumor (TGCT)

Treatment:
After referral to Orthopedic Oncology, patient underwent arthroscopic synovectomy with intra-surgical biopsy. Her pathology results were conclusive for Pigmented Villonodular Synovitis.

Outcome:
Patient did remarkably well after synovectomy. Her swelling remained for approximately two weeks after the procedure then subsided substantially. Her pain decreased significantly within two weeks.

At the three week mark, patient returned to full activity. She was fully weight bearing and began jogging leisurely. She had no orthopedic restrictions and was able to use conservative treatment for any remaining swelling.

Patient was seen at a 10 week follow-up where she was doing well with no pain or swelling. No further imaging was recommended.

Author's Comments:
Pigmented Villonodular Synovitis is a relatively rare condition with a reported 1.8 cases per 1 million people per year. Most studies show no significant differences in gender affected, but some show a slightly higher incidence in males. The typical age of presentation lies between 20-45 years of age. The etiology of the condition remains largely unknown, and there is some argument to whether this is a neoplastic or inflammatory process. PVNS is typically thought to be a benign lesion but can be locally destructive. Some of the complications seen with PVNS are articular cartilage destruction, osteoarthritis, and pain. The recurrence rates of local PVNS are relatively low, with most studies reporting rates around 9%. In the diffuse form, recurrence rates have been reported to be as high as 45%.

This particular case was of great interest due to this patient presenting with a relatively uncommon diagnosis in an even more uncommon manner. Usually patients have a more insidious onset of PVNS. Pain is typically insidious onset with worsening pain over time. In her case, it was a very abrupt onset with an undulating pattern of symptoms.

One of the biggest things to notice is a young person with pain and swelling. Pain can come from many forms, including overuse pattern, but the combination of swelling and pain without any inciting event should cause a higher level of suspicion for a more severe etiology.

Editor's Comments:
Pigmented Villonodular Synovitis more commonly seen in the knee joint but can also involve the ankle, hip, shoulder and elbow joints. It diffusely involves the synovium of the affected joint. The lesion looks like a villous pattern in the synovium, which has a brown or yellowish appearance; the synovial fluid can be hemorrhagic. Treatment is a synovectomy but can reoccur after surgery.
An insidious onset of knee pain and swelling in an otherwise healthy individual should alert the clinician to reactive or neoplastic diagnosis. Labs can be obtained to assess for infection or inflammation. Plain films are essentially normal in this case but an MRI with contrast is the imaging modality of choice. Tissue biopsy is confirmatory.

References:
Frassica, FJ. et al. Pigmented Villonodular Synovitis of the hip and knee. Am Fam Physician. 1999 Oct. 1;60(5): 1414-1410

Tyler, WK. et al. Pigmented Villonodular Synovitis. J Am Acad Ortho Surg. 2006 Jun. 14(6): 376-385

Dynamed Plus: EBSCO Information Services. 1995-present. Record No. 116419. Pigmented Villonodular Synovitis: (Updates 2017 Jun 07). www.dynamed.com

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