Shreyaskumar R. Patel, MD: Let me engage with Dr Tae Won Kim again. With all the things that can be confused with this entity and as rare as it is, can you give us some of your perspective on the clinical radiographic differential diagnosis? What could be the possible entities that someone might get distracted with, in a legitimate manner, because of overlapping features.

Tae Won B. Kim, MD: The first one that comes to mind is not TGCT [tenosynovial giant cell tumor] in all of these patients. As Dr Abraham said, you talk about the more common things. Patients who have a history of gout, certainly gouty tophi in the distal extremities, need to be thought about because they also present with what appears to be swollen joints that are very painful. If they have a history of gout, that can help you delineate that. More common things that we think about include rheumatoid arthritis. We certainly have seen that rheumatoid arthritis with significant synovitis can be confused for TGCT. There are, very rarely, intraarticular sarcomas. Those should not be ruled out as a possibility, although they are exceedingly rare.

When it comes to metastases in other malignancies, sometimes PVNS [pigmented villonodular synovitis] or TGCT tend to be very large and can have a very brownish appearance, pigmented. In superficial joints in the distal extremities, sometimes you see a brownish color around them. There are people who have discussed metastatic melanoma as being a differential diagnosis, although rare, especially in the joint. But I think it’s something we need to think about. Certainly, chronic infections of the joints can cause a very large synovitis, a synovial hypertrophy. Lyme disease is something that needs to be considered in that realm. A chronic infection can cause synovitis. Those would be the clinical differential diagnoses you would want to think about.

Radiologically, oftentimes on x-ray you’ll see something like joint erosion or joint injury. In terms of radiologic diagnoses, especially in the distal extremities such as the hands and the feet, you’ve got to think about calcific tendonitis if there is a calcium deposition within the x-ray. You can sometimes see that on the x-ray. In the joint, the other process that we can see a lot of is synovial chondromatosis, where you see a lot of different, little enlarged masses within the intraarticular space. But those have a very characteristic MRI [magnetic resonance imaging] signal, so they’re not as easily confused with TGCT compared to rheumatoid arthritis.

I don’t order the immunohistochemical stains immediately. Generally, it’s done by a pathologist. When you look at some of the studies on the immunohistochemical profiles of these tumors, CD68 and CD163 are certainly stains that are utilized by our colleagues and in research to look at macrophages, which are a key component of this tumor. The findings have led to the discovery of new drugs for this tumor. That’s how I would go about evaluating and looking at these differential diagnoses.

Transcript Edited for ClaritySupported by an unrestricted educational grant from Daiichi Sankyo.