[Cheryl G]

PET/CT sensitivity in detecting myeloma activity?

by Cheryl G on Mon May 21, 2018 8:43 am

I was surprised to read in a recent post here in the forum that the forum member has an M-spike of 2.6 g/dL and a free light chain ratio of 17.3, yet a recent whole body PET/CT that they had showed no sign of disease activity.

Given the patient's M-spike and free light chain ratio, it's obvious there's active multiple myeloma. So why isn't the PET/CT showing it?

If the PET/CT can't pick up such disease activity, what's its value?

I should note that I don't think this particular case is the only case that's come up in the forum where lab results clearly show disease activity, but a PET/CT scan does not. I thought I saw a similar post not that long ago.

[Multibilly]

Re: PET/CT sensitivity in detecting myeloma activity?

by Multibilly on Mon May 21, 2018 9:05 am

Good morning Cheryl,

I have an M-spike of 2+ g/dL and a free light chain ratio of 13-15, yet my PET/CT scan results show no disease activity. I've always thought the primary value of a PET/CT scan was to detect focal and lytic lesions, as well as extramedullary plasmacytomas (which it can certainly do well). But in the absence of myeloma-related lesions and plasmacytomas, I don't think a PET/CT scan will nec­es­sarily pick up on myeloma disease that is diffusely spread throughout one's marrow. At least, that's always been my assumption, but I could certainly be wrong on this point.

[coachhoke]

Re: PET/CT sensitivity in detecting myeloma activity?

by coachhoke on Mon May 21, 2018 9:49 am

I believe pretty strongly that a PET/CT scan is a very valuable tool in monitoring disease pro­gression. I have many lytic lesions in my spine, but have not shown any activity in over five years, despite my trending upward M-spike. The PET/CT did show activity in my testicles, which turned out to be nothing, and in my prostate, which on biopsy showed a malignancy and was treated with radiation (successfully it seems).

[Cheryl G]

Re: PET/CT sensitivity in detecting myeloma activity?

by Cheryl G on Mon May 21, 2018 10:24 am

Thanks for your feedback, Multibilly and Coachhoke.

I guess I was wrong in assuming that a key benefit of PET/CT was the ability to (reliably) reflect disease activity in most cases of myeloma. I think you're right, Multibilly, that it mainly highlights concentrated activity, whether it be in the area of lesions, or in extramedullary plasmacytomas.

I think what threw me off was what I've seen written occasionally, which is that PET/CT can be a helpful tool in the case of people with nonsecretory myeloma. That may be the case, but not the way I had thought. I had this idea that PET/CT might allow doctors to calculate, in a purely qualitative way, a sort of "visual M-spike," or "visual plasma cell percentage."

As always when it comes to discussing PET and other imaging modalities, it's worth linking to this very helpful forum article by Dr. Kapoor:

"To PET or not to PET" (July 24, 2014)

Thanks!

[moonscape]

Re: PET/CT sensitivity in detecting myeloma activity?

by moonscape on Fri May 25, 2018 5:45 pm

This was the case with me also, Cheryl. I don't recall my numbers at diagnosis right now (it has been about 2.5 years and I'm currently on maintenance therapy and holding), but I had / have lesions in my limbs, but the PET was negative, did not pick any of them up. For that reason, my specialist and I agreed on annual whole-body MRIs, which reminds me I'm due for one!