Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The rare disease that we will be learning about today is:

Tenosynovial Giant Cell Tumor

What is Tenosynovial Giant Cell Tumor?

• Tenosynovial giant cell tumor (TGCT) is a group of usually non-malignant, rare tumors that impact the joints
  • Typically, these tumors develop from the joint lining, or the synovial tissue
• Without treatment, permanent damage to joint mobility can occur
• The disease classified based on whether the tumor appears inside or outside of the joint, as well as the growth pattern of the tumor itself
  • Localized TGCT – Sometimes called giant cell tumor of the tendon sheath, this form of the disease is more common. They tend to develop over several years and are usually benign and do not cause damage to surrounding tissues. The finger joints are most often affected.
  • Diffuse TGCT – Sometimes called pigmented villonodular synovitis, this form of the disease is rarer and can be locally aggressive. The hip and knee are most often impacted.
• The disease is difficult to diagnose and is often confused with other conditions, such as sport injuries, arthritis, xanthomas, etc.

How Do You Get It?

• While it can occur at any age, people age 40 or younger are at a greater risk
• Tenosynovial giant cell tumors grow as a result of the overexpression of colony-stimulating factor 1 receptor, which is caused by a chromosomal translocation
  • However, risk factors for this translocation remain unknown and it appears to occur at random

What Are The Symptoms?

• Localized
  • The main symptom of localized tenosynovial giant cell tumor is swelling of the affected joints, typically of the hands or feet
  • A feeling of instability or “locking” of the joint
  • In some cases, pain may develop
• Diffuse
  • Pain of the affected joint
  • Swelling of the affected joint
  • Stiffness of the joint
  • Generally, these symptoms develop gradually
  • The skin around the joint may be warm and tender
  • Locking of the joint
  • Popping sound with movement
  • Bone erosion
  • Tissue damage
  • Due to local aggression, the disease can expand outside of the joint
    • This can lead to intense pain and permanent loss of movement

How Is It Treated?

• Surgery is the standard method for treating all forms of tenosynovial giant cell tumor
  • Physical therapy may be needed to rehabilitate the joints
  • Unfortunately, recurrence of the disease following surgery is common, particularly for the diffuse form
  • Further surgeries may be needed if the disease recurs, and in some cases even amputation may be recommended
• Sometimes radiation treatment may be useful in recurrent disease, but in recent years, this treatment has mostly been avoided
• CSF1R inhibitors can improve function in recurring disease or in cases that can’t be treated with surgery.

Where Can I Learn More???

• Learn more about this disease from the TGCT Support.
• Check out our cornerstone on this disease here.