Additional Testing for the Diagnosis of hATTR Amyloidosis


John L. Berk, MD: There are a lot of fancy tests that may not be part of the armamentarium for neurologists in the community. I’d like to hear your comments about the applicability and value of these tests. So we’ve talked about EMGs [electromyograms]. That obviously is a universally available modality. How about sympathetic skin response?

P. James B. Dyck, MD: So it’s a test that we don’t use at the Mayo Clinic because we have autonomic reflex screens and thermoregulatory sweat tests and quantitative sensory tests. So we can look at autonomic fibers and we can look at small and large unmyelinated and myelinated fibers through these other tests. But I think when you’re in the community, it is a valuable test for community neurologists to use.

John L. Berk, MD: But you do use sweat tests?

P. James B. Dyck, MD: I absolutely use sweat tests. I use autonomic reflex screen testing, which has a sweat test built into that as well. I use quantitative sensation, which looks at heat pain, which is an unmyelinated fiber modality; cooling, which is a small myelinated fiber modality; and touch and vibration, which are large fiber modalities.

John L. Berk, MD: Michael, QST, sympathetic skin response, and sweat tests?

Michael J. Polydefkis, MD: They’re all useful tools. I think in the community there will be difficulty. QST [quantitative sensory testing] requires equipment and trained people to do it properly. So I’m not sure every community neurologist will find that useful. Sympathetic skin response is not something we’ve had that much experience with. I think we tend to use skin biopsies.

John L. Berk, MD: Heart rate deep breathing?

P. James B. Dyck, MD: The heart rate deep breathing is part of the autonomic reflex screen. It is a useful test, but 1 of the problems in TTR [transthyretin] amyloidosis is that about 20% of the patients will have some sort of arrhythmia, and one can’t use that in those patients.

John L. Berk, MD: Heart rate deep breathing?

Michael J. Polydefkis, MD: I agree with Jim.

John L. Berk, MD: In our experience, we ran into issues of atrial arrhythmias, which confound the test. But in addition, the heart rate deep breathing expressed essentially denervation very early in disease. Is that your experience at the Mayo Clinic, or is that a test that really can detect a spectrum of disease?

P. James B. Dyck, MD: That’s a good question. I don’t know if I’ve thought about it in depth enough to really answer that question. It’s certainly a sensitive test to pick up disease. And so Drs. Phillip Low and my father, Peter Dyck, thought about what was doable for these tests and came up with heart rate deep breathing as probably the most doable thing. The problem is that there is a lot of arrhythmia, so 1 study essentially looked at orthostasis as a surrogate because that was easily done. Even if you had arrhythmia you could find that.

John L. Berk, MD: And your impression about that as a surrogate?

P. James B. Dyck, MD: I think it worked very well in that study, actually. As a community physician, I think doing orthostatic blood pressures is much more doable than doing heart rate deep breathing or other testing.

Akshay S. Desai, MD, MPH: Even a cardiologist can do that.

P. James B. Dyck, MD: Even a cardiologist can do it. Even a hematologist can do that.

John L. Berk, MD: Let’s not stretch reality here. Michael, your feelings about that?

Michael J. Polydefkis, MD: I think heart rate variability with deep breathing is an excellent test in picking up early autonomic dysfunction. Clearly amyloidosis.

John L. Berk, MD: Something that I’m less familiar with: Sudoscans. Do either of you use Sudoscans?

P. James B. Dyck, MD: I do not.

Michael J. Polydefkis, MD: We don’t either.

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