Best way of doing a skin biopsy to diagnose SFN?

[ChookityPop]

Im pretty sure Ive come across the most up to date way to diagnose SFN somewhere.

Im sure it was 2 or 3 sites on the legs they should do the skin biopsy. I want to know so that Im sure they does it correctly. I have a feeling they will just go for one skin biopsy on my ankle after talking to a girl that had the biopsy. I have zero faith that they know what they are doing so I will contact them beforehand to be sure.

I also have positive TS-HDS antibodies so I wont let them rest before they have tested me properly.

 

[katabasis]

I'm glad to hear you're pushing for proper testing for this condition. When I had my skin biopsy done, it was 2 sites - ankle and upper thigh - though I've read that sometimes they check 3 sites along the leg. The reason they test multiple sites is that if the distal sites (furthest from the body) have worse nerve density, the SFN is considered 'length-dependent', which typically indicates diabetes/blood glucose issues. Otherwise, the SFN is considered 'non-length-dependent', which is usually idiopathic (i.e. probably autoimmune). With your antibodies, it's probably the latter, but it is still good to have a little more information.

The biopsy should sample the full thickness of the skin, and the punch size is around 3 mm. The samples are immunostained with an antibody for some nerve protein, which effectively visualizes the small nerve fibers in the skin. These fibers are counted and compared to typical nerve fiber densities for your age/gender. If the doctor confirms these details, I'd assume they know what they are doing.

 

[ChookityPop]

I'm glad to hear you're pushing for proper testing for this condition. When I had my skin biopsy done, it was 2 sites - ankle and upper thigh - though I've read that sometimes they check 3 sites along the leg. The reason they test multiple sites is that if the distal sites (furthest from the body) have worse nerve density, the SFN is considered 'length-dependent', which typically indicates diabetes/blood glucose issues. Otherwise, the SFN is considered 'non-length-dependent', which is usually idiopathic (i.e. probably autoimmune). With your antibodies, it's probably the latter, but it is still good to have a little more information.

The biopsy should sample the full thickness of the skin, and the punch size is around 3 mm. The samples are immunostained with an antibody for some nerve protein, which effectively visualizes the small nerve fibers in the skin. These fibers are counted and compared to typical nerve fiber densities for your age/gender. If the doctor confirms these details, I'd assume they know what they are doing.

Thank you very much for this info! Ive copy pasted it.

I also heard Dr. Oaklander say this:
"Many labs use a threshold (76 ENF/mm2) to interpret skin biopsies as normal or neuropathy among all 105 abnormal MGH biopsies from patients under 40 in 2012-2013, the 76 ENF/ mm2 cutoff would have only detected SFPN in 26 (75% false negative diagnosis rate)

Max developed a multivariate regression that generates normal distribution for each patients biopsy based on that persons age.
MGH is the only lab globally with accurate norms for children and adolescents."

Proably a good thing to ask which threshold they use to be sure.

 

[kangaSue]

Therapath's procedure guide;
https://www.therapath.com/services/small-fiber-neuropathy-testing/small-fiber-procedure/

This article suggests patients would also benefit from determination of clinical phenotypes (different subsets) for better diagnosis and treatment planning;
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5912271/
Small Fiber Neuropathy: Disease Classification Beyond Pain and Burning (2018)

 

[pattismith]

Im pretty sure Ive come across the most up to date way to diagnose SFN somewhere.

Im sure it was 2 or 3 sites on the legs they should do the skin biopsy. I want to know so that Im sure they does it correctly. I have a feeling they will just go for one skin biopsy on my ankle after talking to a girl that had the biopsy. I have zero faith that they know what they are doing so I will contact them beforehand to be sure.

I also have positive TS-HDS antibodies so I wont let them rest before they have tested me properly.

here the paper from Todd Levine, with his diagnostic procedure

Todd Levine Latest paper on Small Fiber Neuropathy sept 2020 | Phoenix Rising ME/CFS Forums

Most of the time, 2 biopsies are enough for a diagnostic, but 3 allows more refined result

 

[ChookityPop]

here the paper from Todd Levine, with his diagnostic procedure

Todd Levine Latest paper on Small Fiber Neuropathy sept 2020 | Phoenix Rising ME/CFS Forums

Most of the time, 2 biopsies are enough for a diagnostic, but 3 allows more refined result

Thanks, this was exactly what I was looking for.

So for Immune mediated SFN like TS HDS they should at least take one biopsy from the thigh since ankle biopsies can be normal according to Todd Levine.

 

[kangaSue]

So for Immune mediated SFN

If you have painful neuropathy, distal stocking hair loss could be another sign of having SFN. I assume this could occur in immune mediated SFN other than just in Diabetes;
https://www.ijem.in/article.asp?iss...=23;issue=5;spage=585;epage=586;aulast=Katrak