Small-Fiber Polyneuropathy May Underlie Dysautonomia in ME/CFS

Miriam E. Tucker

September 02, 2020

A significant proportion of patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and dysautonomia may have potentially treatable underlying autoimmune-associated small-fiber polyneuropathy (aaSFPN), pilot data suggest.

Ryan Whelan

The findings, from a single-site study of 61 patients with ME/CFS, were presented August 21 at the virtual meeting of the International Association for Chronic Fatigue Syndrome/Myalgic Encephalomyelitis by Ryan Whelan, BS, a research assistant at Simmaron Research Institute, Incline Village, Nevada.

Recent evidence suggests an autoimmune etiology for some patients with ME/CFS, which is defined as experiencing for a period of at least 6 months profound, unexplained fatigue, postexertional malaise, and unrefreshing sleep, as well as cognitive dysfunction and/or orthostatic intolerance (OI).

OI is part of a spectrum of autonomic dysfunction commonly seen in ME/CFS patients, which may also include postural orthostatic tachycardia (POTS), peripheral temperature dysregulation and light sensitivity, neuropathic pain, and gastrointestinal complaints. Many of these symptoms overlap those reported by patients with aaSFPN, a common but underdiagnosed neurodegenerative disorder characterized by the loss of peripheral autonomic nerve fibers, Whelan explained.

Findings from the current study show that in more than half of ME/CFS patients, levels of at least one autoantibody were elevated. A majority had comorbid POTS or OI, and over a third had biopsy-confirmed aaSFPN.

"Given the overlap of symptoms and common etiological basis, it may be important to identify ME/CFS patients who present with comorbid aaSFPN, as it has been shown that immune modulatory agents, including intravenous gamma globulin [IVIG], reduce the autonomic symptom burden in aaSFPN patients," Whelan said.

He noted that Anne Louise Oaklander, MD, a neurologist at Massachusetts General Hospital, Harvard Medical School, Boston, and colleagues previously linked aaSFPN with fibromyalgia. In addition, they've found a connection between small-fiber dysfunction and postexertional malaise, which is a hallmark ME/CFS symptom.

Dr Lily Chu

Asked to comment on Whelan's presentation, IACFSME co-president Lily Chu, MD, told Medscape Medical News that the new findings are "valuable, because ME/CFS has always been looked upon as just subjective symptoms. When people have laboratory abnormalities, it can be due to a bunch of other causes, but...here's pathology, here's a biopsy of actual damage. It's not just a transient finding. You can actually see it.... It's a solid concrete piece of evidence vs something that can fluctuate."

Autoantibodies, Autonomic Dysfunction, and Small-Fiber Polyneuropathy

Whelan and colleagues conducted an extensive analysis of medical records of 364 patients with ME/CFS (72% female) to identify potential aaSFPN comorbidity. Such identifications were made on the basis of progress notes documenting autonomic dysfunction, laboratory results for serum autoantibodies, and questionnaire symptom self-reports.

They identified 61 patients as possibly having comorbid aaSFPN. Of those, 52% tested positive for at least 1 of 4 autoantibodies, including antimuscarinic cholinergic receptor 4 (47%), anti-beta-2 adrenergic (27%), antimuscarinic cholinergic 3 (25%), and anti-beta-1 adrenergic (13%). These autoantibodies were linked to ME/CFS in a recent Swedish cohort study.

"Evidence supports that these autoantibodies may bind to receptor sites, blocking ligands from reaching these receptors. Disturbances of adrenergic and cholinergic receptors by these autoantibodies may contribute to symptoms of autonomic dysfunction in ME/CFS," Whelan said.

Although 22% of patients in the study group had POTS and 59% had OI, the authors found no correlation between autoantibody levels and either OI or POTS. However, 38% were confirmed to have small-fiber polyneuropathy on skin biopsy, and the vast majority of those patients (93%) had either POTS or OI.

IVIG May Be a Potential Treatment

Whelan notes that some data suggest that IVIG might help patients with small-fiber neuropathy, including those with autoimmunity.

In addition, he described anecdotal data from a single patient with ME/CFS who had neuropathic symptoms. The patient was treated at Simmaron. The 56-year-old received two IVIG infusions given 6 months apart. The patient experienced a dramatic reduction in levels of all four of the relevant autoantibodies and favorable symptom reduction, as shown in clinician follow-up records. "With the success of this case study, we intend to further evaluate IVIG as a potential treatment in ME/CFS patients. With this research, we hope to identify a subset of ME/CFS patients who will respond favorably to IVIG," Whelan concluded.

Regarding use of IVIG, Chu commented, "We don't know exactly how it works, but it seems to help certain conditions." She pointed to another recent small study that reported clinical improvement in patients with ME/CFS through a different approach, immunoadsorption, for reducing the autoantibody levels.

Overall, Chu said, this line of research "is important because it shows there's some type of abnormal biomarker for ME/CFS. And, it may lay a path toward understanding the pathophysiology of the disease and why people have certain symptoms, and could be used to target therapies.... It's intriguing."

Whelan and Chu have disclosed no relevant financial relationships.

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