# Thickening of Dorsal Foot Nerves: A Frequent Sonographic Finding in Asymptomatic Volunteers, Potentially Leading to False Positive Results

## TL;DR

This study finds that thickening of dorsal foot nerves is common in healthy people, which could lead to incorrect ultrasound diagnoses of nerve compression.

## Contribution

The study reveals that asymptomatic individuals frequently have dorsal foot nerve thickening, challenging ultrasound specificity for diagnosing neuropathies.

## Key findings

- Focal thickening of the deep peroneal nerve was found in 45% of asymptomatic volunteers.
- Thickening occurred most often at the first tarsometatarsal joint and was correlated with cross-sectional area and length.
- Ultrasound findings may lead to false positives in diagnosing anterior tarsal tunnel syndrome.

## Abstract

Objectives: Compression neuropathies such as Anterior Tarsal Tunnel Syndrome are usually associated with focal thickening at the compression site. This study aimed to determine the frequency and location of thickenings of dorsal foot nerves in asymptomatic, healthy volunteers. We hypothesized that focal nerve thickening of dorsal foot nerves is a frequent finding in asymptomatic individuals and occurs at anatomically plausible locations, potentially limiting the specificity of ultrasound in the diagnosis of anterior tarsal tunnel syndrome. Materials and Methods: In this prospective study, the nerves at the dorsal foot were examined with ultrasound in 60 volunteers without clinical signs of neuropathy. Cross-sectional area (CSA) changes along the nerve course were assessed, their anatomical location recorded, and demographic data collected. Results: Focal deep peroneal nerve (DPN) thickening was observed in 45% of participants, with a median CSA of 2.14 mm2 (range: 0.84–5.16) and median length of 3.98 mm (range: 1.46–9.95). The most frequent site was the first tarsometatarsal joint (41%). Thickening occurred across all age groups. Superficial peroneal nerve (SPN) thickening was found in 13.3% of participants, primarily affecting the intermediate branch, with a median CSA of 1.82 mm2 and length of 3.02 mm. No thickening was observed in the sural nerve (SN). A strong correlation was found between CSA and length of DPN thickening (r = 0.67, p < 0.001). Conclusions: Asymptomatic, focal thickening of dorsal foot nerves, particularly the DPN, is a frequent sonographic finding in healthy volunteers. These findings highlight the potential for false-positive ultrasound results and the necessity of correlating imaging findings with clinical examination when evaluating for anterior tarsal tunnel syndrome and similar neuropathies.