Study design: An experimental study of motor and sensory function and psychological distress in subjects with acute whiplash injury.
Objectives: To characterize acute whiplash injury in terms of motor and sensory systems dysfunction and psychological distress and to compare subjects with higher and lesser levels of pain and disability.
Summary of background data: Motor system dysfunction, sensory hypersensitivity, and psychological distress are present in chronic whiplash associated disorders (WAD), but little is known of such factors in the acute stage of injury. As higher levels of pain and disability in acute WAD are accepted as signs of poor outcome, further characterization of this group from those with lesser symptoms is important.
Materials and methods: Motor function (cervical range of movement [ROM], joint position error [JPE]; activity of the superficial neck flexors [EMG] during a test of cranio-cervical flexion), quantitative sensory testing (pressure, thermal pain thresholds, and responses to the brachial plexus provocation test), and psychological distress (GHQ-28, TAMPA, IES) were measured in 80 whiplash subjects (WAD II or III) within 1 month of injury, as were 20 control subjects.
Results: Three subgroups were identified in the cohort using cluster analysis based on the Neck Disability Index: those with mild, moderate, or severe pain and disability. All whiplash groups demonstrated decreased ROM and increased EMG compared with the controls (all P < 0.01). Only the moderate and severe groups demonstrated greater JPE and generalized hypersensitivity to all sensory tests (all P < 0.01). 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 motor or sensory tests.
Conclusions: Acute whiplash subjects with higher levels of pain and disability were distinguished by sensory hypersensitivity to a variety of stimuli, suggestive of central nervous system sensitization occurring soon after injury. These responses occurred independently of psychological distress. These findings may be important for the differential diagnosis of acute whiplash injury and could be one reason why those with higher initial pain and disability demonstrate a poorer outcome.