Generalised muscular hyperalgesia in chronic whiplash syndrome

Abstract

The whiplash syndrome has immense socio-economic impact. Despite extensive studies over the past years, the mechanisms involved in maintaining the pain in chronic whiplash patients are poorly understood. The aim of the present experimental study was to examine the muscular sensibility in areas within and outside the region involved in the whiplash trauma. Eleven chronic whiplash patients and 11 sex and age matched control subjects were included in the study. Before the experiment, the whiplash patients had pain in the neck and shoulder region with radiating pain to the arm. Five patients reported pain that was more widespread. The somatosensory sensibility in the areas over the infraspinatus, brachioradial, and anterior tibial muscles was assessed by pressure stimulation, pin-prick stimulation, and cotton swap stimulation. Infusion of hypertonic saline (5.85%, 0.5 ml) into the infraspinatus and anterior tibial muscles was performed to assess the muscular sensibility and referred pain pattern. The saline-induced muscle pain intensity was assessed on a continuous visual analogue scale (VAS). The distribution of pain was drawn on an anatomical map. The pressure pain thresholds were significantly lower in patients (P<0. 01) compared with controls: infraspinatus (mean 152.2 vs. 172.7 kPa), brachioradial (mean 70.0 vs. 363.8 kPa), and anterior tibial muscle (mean 172.7 vs. 497.8 kPa). The skin sensibility to pin-prick stimulation and cotton swap stimulation was not different between patients and controls. Infusion of hypertonic saline caused significantly higher VAS scores with longer duration in patients compared to control subjects (P<0.01). The area under the VAS-time curve was significantly (P<0.01) increased in patients compared to control subjects after injection into the infraspinatus muscle (mean 4138.1 vs. 780.0 cm s) and anterior tibial muscle (mean 4370.8 vs. 978.7 cm s). The saline infusion caused local pain defined as pain located around the injection site and referred pain areas not included in the local pain area. The area of local and referred pain were significantly larger in patients compared to control subjects (P<0.01). In the control group, the referred pain areas to infusion of hypertonic saline into the anterior tibial muscle were found at the dorsal aspect of the ankle. In contrast, the areas of referred pain were quite widespread in the patient group with both distal and proximal referred pain areas. In the present study, muscular hyperalgesia and large referred pain areas were found in patients with chronic whiplash syndrome compared to control subjects both within and outside the traumatised area. The findings suggest a generalised central hyperexcitability in patients suffering from chronic whiplash syndrome. This indicates that the pain might be considered as a neurogenic type of pain, and new pharmacological treatments should be investigated accordingly.

The role of sternocleidomastoid muscle in simulated low velocity rear-end impacts

“…This eccentric muscle contraction mechanism is consistent with the delayed onset of muscle symptoms observed in whiplash injuries [14,15]. This mechanism also supports the generalized muscular hyperalgesia present in subjects who have experienced whiplash trauma; this generalized central hyperexcitability might be caused through tissue injury [5].…”

Evaluation of Pain Pressure Threshold and Widespread Pain in Chronic Low Back Pain

“…A number of studies have shown central sensitization to be responsible for sensory threshold changes and widespread tenderness, as well as peripheral sensitization (13,14,33). Tissue damage stimulates the release of numerous inflammatory mediators from neurons and immune cells (34), resulting in activation of nociceptors in the injury area and nociceptor hypersensitivity.…”

“…Increased nociceptor sensitivity is expressed by spontaneous firing, enlargement of the neuronal receptive field, and decreased firing threshold (35,36), which is known as the peripheral sensitization-an initiative for pain. Effective changes in tissue sensitivity may develop immediately after injury and the resultant pain because of neurobiological influences (14,37). Then, they may be followed by pain in unrelated sites and persistent exaggerated pain outside of the neuro-anatomical sensory distribution of the primary lesion.…”

“…As a result, pain threshold may be lowered. Although several studies have suggested the involvement of central mechanisms in lowering pain pressure threshold (PPT) in musculoskeletal disorders, such as CLBP (13)(14)(15), the way by which the neuronal mechanisms cause widespread pain and hypersensitivity in patients with CLBP remains controversial. Widespread pain is commonly defined as pain presenting on both sides of the body, above and below the waist, and also involving the axial skeleton (16).…”

Long-term labour-market performance of whiplash claimants

“…The particular injury producing persistent WAD is still, however, not well known, c.f. Johansen et al (1999). 1 A discussion about the existence of chronic WAD is going on in the medical literature, with some researchers attributing chronic disorders to specific injuries and others sceptical towards the existence of persistent WAD (Livingston 2000).…”