Motor system dysfunction, sensory hypersensitivity and psychological distress are features of chronic whiplash associated disorders (WAD). Little is known of such factors in the acute stage of injury or of their changes from transition to either recovery or symptom persistence. Current prognostic indicators of poor outcome following whiplash injury are limited to age, gender and higher levels of initial symptoms.
This prospective longitudinal study measured motor function (cervical range of movement (ROM), joint position error (JPE) and EMG activity of the superficial neck flexor muscles during a test of cranio-cervical flexion), quantitative sensory testing (pressure, thermal pain thresholds and responses to the brachial plexus provocation test (BPPT)), sympathetic vasoconstrictor responses and psychological distress (GHQ-28, TAMPA, IES) in 80 whiplash subjects (WAD II or III) within one month of injury and then two, three and six months post injury. Motor and sensory function was also measured in 20 control subjects. The main aims of the study were threefold: to characterise acute WAD in terms of motor and sensory function and psychological distress and to compare participants with higher and lesser levels of pain and disability; to investigate the prospective longitudinal development of any changes and to compare differences between those who recover and those who report persistent symptoms based on their status at six months post injury; to investigate the capacity of physical measures of motor and sensory function and psychological distress to predict outcome at six months post whiplash injury.
Analysis of data in the early stage of injury (< one month) identified three sub-groups using cluster analysis based on the Neck Disability Index (NDI): those with mild, moderate or severe pain and disability. All whiplash groups demonstrated decreased ROM and increased EMG compared to the controls (all p<0.01). Only the moderate and severe groups demonstrated greater JPE and generalised hypersensitivity to all sensory tests (all p<0.01). There was no difference in reflex vasoconstriction between the groups. The three whiplash subgroups demonstrated evidence of psychological distress although this was greater in the moderate and severe groups. Measures of psychological distress did not impact on between group differences in either motor or sensory tests. Acute whiplash participants with higher levels of pain and disability were distinguished by sensory hypersensitivity suggestive of central nervous system sensitisation occurring soon after injury.
In order to address the second main aim of the study, subjects were classified at six months post injury using scores on the NDI: recovered (<8), mild pain and disability (10-28) or moderate/severe pain and disability (>30). All whiplash groups demonstrated decreased ROM, increased EMG activity, local mechanical hyperalgesia in the cervical spine and psychological distress at one month post injury, although greater deficits were shown in the group with persistent moderate/severe symptoms. ROM loss, local mechanical hyperalgesia and psychological distress resolved in recovered participants and those with residual mild symptoms at six months, however increased EMG activity persisted in these two groups. In addition to these impairments, the group with persistent moderate/severe symptoms also showed generalised hypersensitivity to all stimuli, increased JPE, increased levels of acute posttraumatic stress and a tendency for impaired vasoconstriction. These changes persisted from soon after injury until the final assessment point (six months post injury). Psychological distress did not impact on measures of motor and sensory function. These findings suggest the presence of more profound disturbances in the underlying mechanisms occurring in those whose with persistent moderate/severe pain following whiplash injury.
The best predictors of outcome at six months post injury (NDI score at six months) were higher initial levels of pain and disability (NDI), older age, female gender, decreased cervical ROM, decreased cold pain threshold, impaired vasoconstriction, higher pain scores with the BPPT and higher levels of acute posttraumatic stress (IES). These variables together accounted for 67% of the variability in NDI scores at six months. This is the first time that physical and psychological factors in addition to the already recognised predictors of outcome (demographic and symptomatic factors) have been shown to be associated with poor recovery following whiplash injury. Addressing these changes soon after injury may prevent the transition from the acute to chronic stages of the condition.