Intramuscular fat is present in cervical multifidus but not soleus in patients with chronic whiplash associated disorders.

Ashley Pedler,Gail Durbridge,Graham Galloway,Michele Sterling,Katie Mcmahon,Alejandro A Espinoza Orías

doi:10.1371/journal.pone.0197438

Abstract

The presence of intramuscular fat (IMF) in the cervical spine muscles of patients with whiplash associated disorders (WAD) has been consistently found. The mechanisms underlying IMF are not clear but preliminary evidence implicates a relationship with stress system responses. We hypothesised that if systemic stress system responses do play a role then IMF would be present in muscles remote to the cervical spine. We aimed to investigate if IMF are present in muscle tissue remote (soleus) to the cervical spine in people with chronic WAD. A secondary aim was to investigate associations between IMF and posttraumatic stress symptom levels. Forty-three people with chronic WAD (25 female) and 16 asymptomatic control participants (11 female) participated. Measures of pain, disability and posttraumatic stress symptoms were collected from the WAD participants. Both groups underwent MRI measures of IMF in cervical multifidus and the right soleus muscle. There was significantly greater IMF in cervical multifidus in patients with WAD and moderate/severe disability compared to controls (p = 0.009). There was no difference in multifidus IMF between the mild and moderate/severe disability WAD groups (p = 0.64), or the control and mild WAD groups (p = 0.21). IMF in the right soleus was not different between the groups (p = 0.47). In the WAD group, we found no correlation between PDS symptoms and cervical multifidus IMF or between PDS symptoms and soleus IMF. Global differences in IMF are not a feature of chronic WAD, with differences in IMF limited to the cervical spine musculature. While the mechanisms for the development of IMF in the cervical spine following whiplash injury remain unclear, our data indicate that local factors more likely contribute to these differences.

Highlights

Identifiable pathological causes for ongoing pain in whiplash associated disorders (WAD) remain elusive
Intramuscular fat in whiplash associated disorders. The exception to this are recent magnetic resonance imaging (MRI) studies that have identified the presence of higher levels of intramuscular fat (IMF) in people with WAD when compared to asymptomatic controls and people with non-traumatic neck pain [4,5,6]
Posttraumatic stress symptom levels were a significant mediator of the relationship between initial pain and later levels of IMF [9] implicationg stress system responses in the development of IMF

Summary

Introduction

Identifiable pathological causes for ongoing pain in whiplash associated disorders (WAD) remain elusive. Imaging studies have generally failed to find a higher prevalence of cervical spine pathology in people post whiplash injury than in asymptomatic controls [1,2,3]. The exception to this are recent magnetic resonance imaging (MRI) studies that have identified the presence of higher levels of intramuscular fat (IMF) in people with WAD when compared to asymptomatic controls and people with non-traumatic neck pain [4,5,6]. A longitudinal investigation found that these fatty deposits develop between 2 and 12 weeks post whiplash injury and are significantly greater in people with poor functional recovery at 6 month follow up [7].

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