The incidence of small fiber neuropathy has been increasing and it presents differently from large fiber neuropathy, according to a new study from the United States. While the large fiber neuropathy presents with loss of joint position and vibration sense and sensory ataxia, the symptoms of small fiber neuropathy are numbness, tingling and pain in the feet.

The records of over two decades, of 94 individuals residing in Olmsted County, Minnesota diagnosed with small fiber neuropathy were examined. The control group comprised of 282 people of similar age and sex who did not have neuropathy. The participants were followed for an average of 6 years.

In the study published in the journal Neurology, the incidence of small fiber neuropathy was found to be 13.3 per 100,000 people. The incidence was higher in females (67%) than in males.

Compared to a BMI of 28.5 in persons without neuropathy, the average BMI of persons with neuropathy was 30.4 indicating that the patients were obese. More participants with small fiber neuropathy reported insomnia (86% versus 54%, respectively). They also had higher odds of suffering a heart attack (46% versus 27%, respectively), being diabetic (51% versus 22%) and having high triglycerides (180 mg/dL versus 147 mg/dL, respectively). They were also more likely to take opioids for pain relief (72% versus 46%, respectively).

No cause could be discerned in 70%, while in 15% individuals, diabetes was determined as the cause of neuropathy. Sjögren syndrome (2%), AL-amyloid (1%), transthyretin-amyloid (1%), lupus (1%), Fabry’s disease (1%), post-viral (1%) were identified as the other causes. In 5% of individuals, the neuropathy was multifactorial.

Thirty-six percent of those with small fiber neuropathy progressed to large fiber neuropathy around 5 years after the onset of small fiber neuropathy.

This study has defined the incidence of small fiber neuropathy and also determined the comorbid conditions.

Even though the neuropathy was idiopathic in the majority, this study has shown that individuals with small fiber neuropathy were more likely to be female, obese and diabetic. Major neurological impairments and disability are uncommon but given the association with obesity and diabetes, persons with symptoms of small fiber neuropathy should be regularly screened and monitored for diabetes and other risk factors for cardiovascular disease such as obesity, high triglycerides. Rheumatologic and genetic causes too should be looked for. Hence, timely preventive measures and initiation of targeted treatment is essential.

Reference

1. Johnson SA, et al. Small fiber neuropathy incidence, prevalence, longitudinal impairments, and disability. Neurology. 2021 Oct 27;10.1212/WNL.0000000000012894. doi: 10.1212/WNL.0000000000012894.