The Curbsiders' 'Hot Takes'

MGUS, SPEP, and the Shaka Sign

The Curbsiders


February 05, 2021

This transcript has been edited for clarity.

Matthew F. Watto, MD: I am Dr Frank Watto, and that is Dr Stuart K. Brigham. With us is our good friend, Dr Paul Nelson Williams.

Paul N. Williams, MD: This time around we are going to talk about our episode with Dr Jorge Castillo on monoclonal gammopathy of undetermined significance (MGUS) and interpreting the notorious serum protein electrophoresis (SPEP) test. We'll start with Stuart and find out what takeaway points he gleaned from this episode.

Stuart K. Brigham, MD: My takeaway is a way to understand SPEP using the "shaka sign."


You have the albumin, alpha 1, alpha 2, beta, and gamma region. What you should see is the smooth appearance of the gamma region, but if you have a gammopathy in the gamma region, you'll see a spike. That's why it's called M-spike. If you have a polyclonal gammopathy, it shifts the albumin:globulin ratio.

To springboard on that, what I took away from the episode is the importance of immunofixation in identifying that protein in the gamma region and how to interpret it.

Watto: The SPEP tells you whether there is an M-spike, meaning that some kind of monoclonal protein is being produced. Immunofixation tells you whether it's IgG, IgM, IgA. Is it a light chain? It basically tells you the specificity.

One of the biggest points for me from this episode was the "big three" in MGUS. MGUS is where you have a monoclonal protein, and MGUS doesn't often progress to anything. About 1% a year progresses to multiple myeloma. An IgM type of MGUS progresses a little more, maybe 1.5%.

The big three are multiple myeloma, amyloidosis, and Waldenstrom's macroglobulinemia. The illness scripts for those are relatively simple and really good to just keep in your back pocket.


For multiple myeloma, think CRAB: C (hypercalcemia); R (renal abnormality; usually elevated creatinine); A (anemia); and B (bone lesions). That's why we get a bone survey looking for lytic lesions.

Amyloidosis can cause cardiac abnormalities, macroglossia, nephrotic syndrome, and a type of neuropathy. Dr Castillo pointed out that patients can have both a motor and sensory neuropathy, and associated muscle wasting, which is different from the typical diabetic neuropathy.

Finally there is Waldenstrom's macroglobulinemia, which is really more of a lymphoma. Waldenstrom's has anemia as well as hyperviscosity syndrome. I had no idea what that meant.

Williams: This was a really helpful illness script, because Waldenstrom's was something that I knew for the boards at one point but I've probably forgotten about and don't think about much. Dr Castillo made the point that you could potentially save a patient's life if you have the right threshold of suspicion.

In terms of the hyperviscosity seen in Waldenstrom's, you have the epistaxis but you also have symptoms that should tip you off, including persistent headache and blurred vision that doesn't correct with glasses. There are all sorts of characteristic findings on fundoscopic examination.

This can get somewhat confusing, so don't fear referral. In amyloidosis, if you have the pathologic tissue diagnosis, congratulations; but if you don't, it doesn't mean the patient doesn't have it. If you aren't sure what to do, this is a great time to call on your friendly neighborhood hematologist. Even MGUS, which is recognized as benign, can progress, so they have to monitor and know what fancy-pants labs to order. It's okay to be confused because we all are. I was certainly helped by this episode. Just don't be afraid to call hematology if you aren't sure what to do.

Watto: One more thing about Waldenstrom's that I'm not sure I mentioned earlier: The neuropathy associated with it is more of a peripheral neuropathy that tends to involve the hands and the feet. If someone has a symmetrical distal neuropathy and it doesn't quite make sense because they don't have diabetes, this might be something to think about. It's different from amyloidosis because there's no motor involvement with this one.

This was a really complicated topic and our guest did a great job of explaining it. To hear the full episode, go to #247: SPEP It Up, or find The Curbsiders' podcasts on iTunes.

You can read our show notes on that episode and join our mailing list. Thank you for watching.

The Curbsiders are a national network of students, residents, and clinician educators from across the country, representing 15 different institutions. They "curbside" experts to deconstruct various topics in the world of medicine to provide listeners with clinical pearls, practice-changing knowledge, and bad puns. Learn more about their contributors and follow them on Twitter.

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