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    Created in 2008, Phoenix Rising is the largest and oldest forum dedicated to furthering the understanding of, and finding treatments for, complex chronic illnesses such as chronic fatigue syndrome (ME/CFS), fibromyalgia, long COVID, postural orthostatic tachycardia syndrome (POTS), mast cell activation syndrome (MCAS), and allied diseases.

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Senior Member
U.S., Earth
The orthostatic intolerance is caused by dysautonomia, which can include autonomic neuropathy, where the autonomic nerves that control the veins in the legs fail to constrict properly upon standing, leading to blood pooling in the legs. So, in this sense, autonomic neuropathy contributes to orthostatic intolerance.

But, because of the orthostatic intolerance and the blood pooling, there is not enough oxygen to support the small-fiber nerves in the feet and ankles, leading to the death of the small-fiber nerves. So, in this sense, orthostatic intolerance contributes to small-fiber neuropathy.

Related thread:
Insights from Invasive Cardiopulmonary Exercise Testing of Patients with ME/CFS (Joseph et al., 2021)


Senior Member
I'm very interested!, since we seem to respond to the same treatments: caffeine, corticosteroids, modafinil etc..

@S-VV ,
actually I already know I have SFN, I am investigating the cause. A nice neurologist gave me the opportunity to test for genetic SFN, but I am convinced that I have an auto-immune/inflammatory process at play.
I have both immunodeficiency and past auto-immunity.
If these research antibodies are positive, docs may listen to me (or not) :)


Senior Member
@pattismith I just posted this somewhere else, so I'm copy/pasting here for you. You may be interested.

I wanted to share what I’ve found/learned regarding the Complement system (part of the immune system), and treatment/peptides for Complement dysfunction I’ve found.​
Most people do not know about the Complement system. But there’s a good chance that many here have symptoms due to either dysregulation, impairment, or inadvertent activation of complement components.​

  • Deficiencies of complement components are associated with increased susceptibility to infections
  • Complement system dysfunction creates an imbalance of both host defense and inflammatory response leading to autoimmunity
  • Uncontrolled complement activation can lead to inflammatory issues, autoimmune disorders, alterations of blood flow, and tissue destruction
The complement system is pretty complicated. There’s def a learning curve to being able to wrap your head around the general idea. And instead of going over all complement formation details, I’ll just say this – there are many components, proteins, and regulators involved in the complement system. One is C5, and therapeutic targeting on C5 I believe can benefit a lot of people here, especially w/ autoimmune issues, fatigue, and pain.​
Complement component 5 (C5) is involved towards the end of the “cascade”. When C5 is cleaved, it creates C5a and C5b. From here, it can end up forming what’s called the Membrane Attack Complex (MAC) or Terminal Complement Complex (TCC), which is made up of C5b-9.​
Inadvertent MAC (C5b-9) formation can result in autoimmune destruction, and is seen in numerous autoimmune diseases. I myself only started looking into this after learning about my Small Fiber Neuropathy with TS-HDS IgM antibodies, and how it’s associated w/ C5b-9 deposits in the capillaries at the sites of nerve damage. Then I learned that C5b-9 is found in skin biopsies of patients w/ Guttate Psoriasis, another thing I have. So, I started looking more into it and looking for inhibitors, and treatment for something like this.​
Usually, you want to inhibit C5, because if you inhibit one of the earlier components, you might risk dysfunction throughout the rest of the cascade.​
At first I just found the super-expensive Eculizumab, which is IVIG. But recently found multiple other C5 inhibitors that are subcutaneous. Here’s all the c5 inhibitors I’ve found.​

  • Eculizumab (Soliris)
  • Ravulizumab (Ultomiris, ALXN1210)
  • Zilucoplan (RA101495) – Subcutaneous - 0.3 mg/kg zilucoplan daily
  • Tesidolumab (LFG316)
  • Pozelimab (REGN3918) – Subcutaneous – 800 mg weekly
  • Crovalimab (SKY59) – Subcutaneous (680 mg; 4 mL), administered once every 4 weeks, complete and sustained terminal complement pathway inhibition; improvements in fatigue, physical functioning, and global health status/QoL; sustained and effective suppression of complement activation
Here are some of the conditions I’ve found that a C5 inhibitor can help treat (I’m sure there’s more, this is just what I’ve found thus far).​

  • Small Fiber Neuropathy
  • Paroxysmal nocturnal hemoglobinuria (PNH)
  • Atypical haemolytic uraemic syndrome (aHUS)
  • Myasthenia gravis
  • Neuromyelitis optica spectrum disorder (NMOSD)
  • Guillain–Barré syndrome (GBS) variants, particularly acute motor axonal neuropathy, acute motor and sensory axonal neuropathy and Miller–Fisher syndrome
  • Lambert–Eaton myasthenic syndrome (LEMS)
  • Dermatomyositis
  • Diabetic Neuropathy
  • Idiopathic membranous nephropathy (IMN)
  • Thrombotic microangiopathy
  • Necrotizing autoimmune myositis (NAM)
  • COVID-19 and COVID-19 ARDS
  • Psoriasis
National Jewish Health Advanced Diagnostic Laboratories is a good place to test for complement activation.

These are all good things to test for:
  • Factor H – Levels, function
  • Factor I – Levels, function
  • Bb - Levels
  • C4a – Levels
  • C4d – Levels
  • C5a – Levels (prob the link between complement activation and pain)
  • SC5b-9 – Levels
  • C1-INH – Levels, function
  • C3 – Function
  • C3a – Levels
  • C3b - Levels
  • iC3b - Levels
  • Properdin – Levels
  • Vitronectin/S-protein – Levels, function
  • MBL – Levels
  • CR1 - Levels

Florida Guy

Senior Member
I don't know if this applies to small fiber neuropathy but I have had neuropathy in my legs and I have been able to keep it under control. What I use is the amino acid l glutamine. You can buy it in bulk. I take a spoonful a day to get over it when it acts up.

It works within a few days for me. I take it now daily just in case along with creatine and a bunch of other things