Fiber medicine

Small-fiber neuropathy on the rise in the US, but why it’s a mystery

Over the past two decades, there has been a significant increase in the number of adults in the United States with small fiber neuropathy (SFN), but in many cases, no cause can be determined.

The exact reason for the increase in isolated SFNs “remains unclear,” said Christopher J. Klein, MD, of the Mayo Clinic in Rochester, Minnesota. Medscape Medical News.

However, “we noted during the study period that the population had an increase in BMI, which appears to be a risk factor for this disorder, with many (50%) developing either an alteration in blood sugar levels is frank diabetes during the study period, although it is not present at the onset presenting small fiber neuropathy, also associated with higher triglyceride levels, ”he explained.

The study was published online on October 27 in Neurology.

Significant upward trend

Investigators looked at the records of 94 adults diagnosed with pure SFN (no significant fiber involvement) between 1998 and 2017 in Olmsted and adjacent counties in Minnesota – and compared them to 282 adults of the same age and the same. sex that did not have neuropathy.

The incidence of SFN over the entire study period was 1.3 per 100,000 per year and the prevalence was 13.3 per 100,000.

There was a “significant upward trend” in the incidence of SFN over the study period that could not be attributed to the availability of intraepidermal nerve fiber density testing, the authors report.

The median age of onset of SFN was 54 years, and two-thirds were female (67%).

Diabetes, obesity, and hypertriglyceridemia were significantly more common in patients with SFN than in matched controls. These metabolic risk factors are also associated with peripheral neuropathy regardless of the type of fiber.

Autonomic symptoms were common and generally mild, affecting 85% of patients with SFN, and included erectile dysfunction in men, constipation, dizziness and palpitations, urinary symptoms, diarrhea, eye and blood pressure. dry mouth, sweat abnormalities and gastroparesis.

Insomnia and the use of opioid analgesics were more common in people with DFS than in matched controls.

More than a third (36%) of patients with SFN developed coarse fiber neuropathy on average 5.3 years after developing SFN.

During a mean follow-up of 6.1 years, adults with NBS were significantly more likely to have a myocardial infarction (46% vs. 27%; odds ratio [OR] 2.0; 95% CI, 1.8 – 4.9), congestive heart failure (27% vs. 12%; OR, 2.6; 95% CI, 1.4 – 4.8), peripheral vascular disease (22% vs. 6%; OR, 4.0; 95% CI, 1.9 – 8.1), stroke (24% vs. 10%; OR, 2.8; 95% CI: 1.5 – 5 , 3), diabetes (51% vs. 22%; OR, 4.6; 95% CI, 2.8 – 7.6) and rheumatologic disease (30% vs. 7%; OR, 5.3; 95% CI %, 2.8 – 10.4).

For 70% of the patients, no cause of SFN could be determined. Diabetes (15%) was the most frequently identified cause. Other less common causes included Sjögren’s syndrome, lupus, amyloidosis, and Fabry disease.

“It is important to quantitatively diagnose patients with SFN because there are many non-neurologic musculoskeletal causes that can mimic the disorder,” Klein said.

“While the rates of progression are rapid, sinister causes such as uncontrollable, hereditary diabetes [transthyretin] TTR amyloidosis and Fabry disease may be responsible. For the rest of the patients, the rates of progression are slow and usually don’t cause significant neurological damage, ”he added.

“However,” he said, “internal medicine follow-up is important for everyone, as this disorder is associated with development with a higher risk of cardiovascular disease, usually including heart attacks.”

It should be noted that although the mean age at death was not significantly different in patients with SFN compared to controls (70 versus 73 years), there was a significantly higher number of deaths in patients with SFN. of SFN (n = 18; 19%) than in matched controls (n = 35; 12%) from the time of symptom onset, the researchers report.

Important research

This ‘important’ study sheds light on co-morbidities and longitudinal consequences of NBS, write Brian Callaghan, MD, with University of Michigan, Ann Arbor, and J. Robinson Singleton, MD, with University of Utah , Salt Lake City, in an accompanying editorial in Neurology.

The study clearly demonstrates that SFN has “similar metabolic risk factors to those seen for predominantly sensory peripheral neuropathies affecting a wider range of fiber types. As a result, therapies that address metabolic risk factors are likely to ‘help prevent or treat both conditions,’ they write.

Callaghan and Singleton add that one of the strengths of the study is the detailed tracking that examines the progression of DFS over time.

“The authors found that patients with DFS do not report high disability and that progression tends to be slow. Therefore, patients with DFS can be told that progression and disability are likely to be modest in most cases. However, when patients progress rapidly, one must look for uncommon etiologies, “write the editorial writers.

The study was supported by the Mayo Clinic Foundation, the Mayo Clinic Center for Individualized Medicine, and the Mayo Clinic Center of MS and Autoimmune Neurology. Klein has received teaching fees from Ackea Pharmaceuticals for lectures on Hereditary Transthyretin Amyloidosis and Fabry Disease, has been consulted for Pfizer regarding tafamidis (all consulting fees go directly to Mayo Clinic), and participated in clinical trials for inotersen and patisiran but received no personal compensation for participating. Callaghan consults for DynaMed, performs forensic consultations, including consultations for the Vaccine Injury Compensation Program, and receives research support from the American Academy of Neurology. Singleton consulted for Regenacy.

Neurology. Published online October 27, 2021. Summary, Editorial

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