Blink reflex changes in parkinsonism following severe traumatic brain injury correlates with diffuse axonal injury

BACKGROUND: Survivors of severe traumatic brain injury (TBI) may show transient or persistent extrapyramidal symptoms such as rigidity, akinesia and parkinsonian posture, associated with hypomimia, not estinguishable glabellar tap reflex, seborrhea and hypersalivation. The Blink Reflex (BR), an electrically-induced reflex, is abnormal in Parkinson's disease (PD) and in some parkinsonisms. The aim of the study was to investigate BR habituation and its recovery cycle in survivors of severe TBI suffering from parkinsonian syndrome and the possible correlation with neuroimaging findings. MATERIAL/METHODS: Twenty-three patients (18 males, 5 females; mean age 23.7 years, range 13-35), who sustained a severe TBI, (Glasgow Coma Scale or GCS, lower than 8 in the first 48 hours), and followed by coma for a duration equal or longer than 15 days, were studied during the post-acute or chronic phase. Enrollement criteria include the presence of at least 3 extrapyramidal symptoms. BR was elicited by electrical stimulation of the supraorbital nerve and responses were recorded with surface electrodes from the orbicularis oculi muscle ipsilateral to the stimulation. A repeated series of 10 electrical stimuli was applied at the frequencies of stimulation of 0.3, 0.5, 0.7, 1.0, 1.5, 2.0 and 3.0 Hz, respectively. Values between 0.5 and 1 Hz were considered as normal, according to the international literature, Cerebral Magnetic Resonance (C-MRI), with fast sequences was performed within 3 months after brain injury. Ten healthy subjects, age and sex matched, served as controls and underwent the same procedure. RESULTS: Nineteen of the twenty-three patients (82.6%) showed a significantly reduced BR habituation in comparison with controls. This findings highly correlated with C-MRI diagnosis of Diffuse Axonal Injury (DAI). A normal BR habituation was found in only 4 out of 23 patients (17%). In these subjects, C-MRI revealed focal lesions rather than DAI. CONCLUSIONS: BR changes correlate with parkinsonian signs and neuroimaging findings. BR may have a role as a diagnostic tool in post-traumatic parkinsonism and as a prognostic tool to evaluate the effect of therapeutic options.