Rate of small fiber neuropathy increasing

Small fiber neuropathy appears to have an increasing incidence rate, with greater trends toward obesity, according to study results published in Neurology.

“Much of the earlier research on [small fiber neuropathy] SFN individually or in combination has not included longitudinal outcomes, detailed neurological examinations, or excluded patients with development of large fiber involvement,” co-first authors Stephen A. Johnson, MD, Kamal Shouman, MD, and Shahar Shelly, MD, and colleagues, all of Mayo Clinic, wrote. “This is important, as small and large fiber dysfunction often coexist, but painful SFN symptoms are often the presenting symptom and the predominant patient concern.”

Because of limited population-based data on SFN, the researchers aimed to investigate SFN incidence, prevalence, comorbidities, longitudinal impairments and disabilities in the current study. They compared 94 test-confirmed patients with SFN (mean onset age, 54 years) between 1998 and 2017 in Minnesota counties in a 3:1 ratio with matched controls.

During the study, SFN incidence increased from 1.3 cases per 100,000 a year to 13.3 cases per 100,000 a year, with an average follow-up of 6.1 years. Those with SFN were more likely to be women and obese, and to have insomnia, an analgesic-opioid prescription, hypertriglyceridemia and diabetes mellitus. Patients with SFN did not self-identify as disabled and had a median modified Rankin scale score of one compared with zero for controls. Patients had higher Charlson comorbidities compared with controls. Further, 46% of patients had myocardial infarctions compared with 27% of controls.

Patients had the following classifications: idiopathic (70%), diabetes mellitus (15%), Sjögrens (2%), AL-amyloid (1%), transthyretin-amyloid (1%), Fabry (1%), lupus (1%), post viral (1%), Lewy body (1%) and multifactorial (5%). A total of 17 patients had foot ulcers, of which 71% occurred in those with diabetes mellitus. Large fiber neuropathy occurred among 36%, with an average of 5.3 years from SFN onset.

Researchers noted a median onset Composite Autonomic Severity Score (CASS) of three, with a change per year of 0.08, as well as a Neuropathy Impairment Score (NIS) of two at onset and an increase of one per year. A change in NIS and CASS of greater than one point per year occurred only for AL-amyloid, hereditary transthyretin-amyloid, Fabry, uncontrolled diabetes mellitus and Lewy body. A total of 19% of patients with SFN died since symptom onset compared with 12% of controls.

“We unexpectedly found a high rate of cardiovascular disease in affected patients,” co-author Christopher J. Klein, MD, told Healio Neurology. “Although the most common group (ie, idiopathic) did not develop major neurologic disabilities, they had greater risks to develop diabetes, and 50% suffered heart attacks, suggesting all diagnosed patients need internal medicine follow-up with aggressive surveillance for development of diabetes and heart disease.”