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Abstract
Background and Objectives There are limited population-based data on small fiber neuropathy (SFN). We wished to determine SFN incidence, prevalence, comorbid conditions, longitudinal impairments, and disabilities.
Methods Test-confirmed patients with SFN in Olmsted, Minnesota, and adjacent counties were compared 3:1 to matched controls (January 1, 1998–December 31, 2017).
Results Ninety-four patients with SFN were identified, with an incidence of 1.3/100,000/y that increased over the study period and a prevalence of 13.3 per 100,000. Average follow-up was 6.1 years (0.7–43 years), and mean onset age was 54 years (range 14–83 years). Female sex (67%), obesity (body mass index mean 30.4 vs 28.5 kg/m2), insomnia (86% vs 54%), analgesic-opioid prescriptions (72% vs 46%), hypertriglyceridemia (180 mg/dL mean vs 147 mg/dL), and diabetes (51% vs 22%, p < 0.001) were more common (odds ratio 3.8–9.0, all p < 0.03). Patients with SFN did not self-identify as disabled with a median modified Rankin Scale score of 1.0 (range 0–6) vs 0.0 (0–6) for controls (p = 0.04). Higher Charlson comorbid conditions (median 6, range 3–9) occurred vs controls (median 3, range 1–9, p < 0.001). Myocardial infarctions occurred in 46% vs 27% of controls (p < 0.0001). Classifications included idiopathic (70%); diabetes (15%); Sjögren disease (2%); AL-amyloid (1%); transthyretin-amyloid (1%); Fabry disease (1%); lupus (1%); postviral (1%); Lewy body (1%), and multifactorial (5%). Foot ulcers occurred in 17, with 71% having diabetes. Large fiber neuropathy developed in 36%, on average 5.3 years (range 0.2–14.3 years) from SFN onset. Median onset Composite Autonomic Severity Score (CASS) was 3 (change per year 0.08, range 0–2.0). Median Neuropathy Impairment Scale (NIS) score was 2 at onset (range 0–8, change per year 1.0, range −7.9 to +23.3). NIS score and CASS change >1 point per year occurred in only AL-amyloid, hereditary transthyretin-amyloid, Fabry, uncontrolled diabetes, and Lewy body. Death after symptom onset was higher in patients with SFN (19%) vs controls (12%, p < 0.001), 50% secondary to diabetes complications.
Discussion Isolated SFN is uncommon but increasing in incidence. Most patients do not develop major neurologic impairments and disability but have multiple comorbid conditions, including cardiovascular ischemic events, and increased mortality from SFN onsets. Development of large fiber involvements and diabetes are common over time. Targeted testing facilitates interventional therapies for diabetes but also rheumatologic and rare genetic forms.
Glossary
- ARS=
- autonomic reflex screen;
- BMI=
- body mass index;
- CASS=
- Composite Autonomic Severity Score;
- CCI=
- Charlson Comorbidity Index;
- CI=
- confidence interval;
- ICD-10=
- International Classification of Diseases, 10th revision;
- IENF=
- intraepidermal nerve fiber;
- IgG=
- immunoglobulin G;
- mRS=
- modified Rankin Scale;
- NIS=
- Neuropathy Impairment Scale;
- QSART=
- quantitative sudomotor autonomic reflex test;
- QST=
- quantitative sensory testing;
- SFN=
- small fiber neuropathy;
- TST=
- thermoregulatory sweat test;
- VGKC=
- voltage gated potassium channel
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
↵* These authors contributed equally to this work.
Editorial, page 1015
CME Course: NPub.org/cmelist
Podcast: NPub.org/Podcast9722
- Received April 27, 2021.
- Accepted in final form September 24, 2021.
- © 2021 American Academy of Neurology
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