Subjective and objective responses to caloric stimulation help separate vestibular migraine from other vestibular disorders.

BACKGROUND: Nystagmus generated during bithermal caloric test assesses the horizontal vestibulo-ocular-reflex. Any induced symptoms are considered unwanted side effects rather than diagnostic information. AIM: We hypothesized that nystagmus slow-phase-velocity (SPV) and subjective symptoms during caloric testing would be higher in vestibular migraine (VM) patients compared with peripheral disorders such as Meniere's disease (MD) and non-vestibular dizziness (NVD). METHODS: Consecutive patients (n = 1373, 60% female) referred for caloric testing were recruited. During caloric irrigations, patients scored their subjective sensations. We assessed objective-measures, subjective vertigo (SVS), subjective nausea (SNS), and test completion status. RESULTS: Nystagmus SPV for VM, MD (unaffected side), and NVD were 29 ± 12.8, 30 ± 15.4, and 28 ± 14.2 for warm irrigation and 24 ± 8.9, 22 ± 10.0, and 25 ± 12.8 for cold-irrigation. The mean SVS were 2.5 ± 1.1, 1.5 ± 1.33, and 1.5 ± 1.42 for warm irrigation and 2.2 ± 1.1, 1.1 ± 1.19, and 1.1 ± 1.16 for cold-irrigation. Age was significantly correlated with SVS and SNS, (p < 0.001) for both. The SVS and SNS were significantly higher in VM compared with non-VM groups (p < 0.001), and there was no difference in nystagmus SPV. VM patients SVS was significantly different to the SVS of migraineurs in the other diagnostic groups (p < 0.001). Testing was incomplete for 34.4% of VM and 3.2% of MD patients. To separate VM from MD, we computed a composite value representing the caloric data, with 83% sensitivity and 71% specificity. Application of machine learning to these metrics plus patient demographics yielded better separation (96% sensitivity and 85% specificity). CONCLUSION: Perceptual differences between VM and non-VM patients during caloric stimulation indicate that subjective ratings during caloric testing are meaningful measures. Combining objective and subjective measures could provide optimal separation of VM from MD.

EMG responses evoked by the termination of galvanic (DC) vestibular stimulation: 'off-responses'.

OBJECTIVE: Vestibular responses in soleus electromyography (EMG) evoked by the sudden onset of galvanic (DC) stimulation ('on-responses') have been described in detail previously. The aim of the present study was to describe responses in soleus triggered by the termination of galvanic stimulation ('off-responses'). METHODS: In 10 healthy human subjects, we studied responses to transmastoid (bilateral) stimuli of 200 ms and 2 s average duration and 3 or 4 mA intensity. We obtained both on- and off-responses using the same raw data. EMG activity was recorded onto tape while current pulses of systematically varying duration were delivered. Averaged on-responses were obtained by triggering from the beginning of the current pulses. Averaged off-responses were obtained by triggering from the termination of the current pulses. RESULTS: Short-latency (SL) and medium latency (ML) off-responses were both obtained in all but one study. The SL and the ML components of the off-responses were present and had similar latencies and amplitudes, but opposite excitability, to the on-responses obtained with the same stimuli. CONCLUSIONS: Off-responses to galvanic vestibular stimulation can be recorded from soleus EMG. Our findings imply that vestibular SL and ML reflex responses in the legs are dependent on the change in the rate of vestibular nerve discharge, not its absolute level. Both on- and off-responses have properties appropriate to a role in maintaining body stability.