Results

Clinical characteristics
The present study included 38 females with migraine without aura, 30 episodic TTH and 50 healthy controls. Mean age in the migraine, TTH and control groups was 35.5, 33.3 and 35.1 years, respectively. The mean age did not differ significantly among groups. Clinical and headache characteristics are shown in Table 1.
Table 1 Clinical and headache characteristics of the study groups
TTH (n = 30) Migraine (n = 38) Control (n = 50) P-value
Age (years) 33.37 ± 13.70 35.58 ± 12.26 35.14 ± 13.47 NS
Frequency (day/week) 1.52 ± 0.93 2.14 ± 2.05 -
Duration (hours/day) 5.35 ± 6.01 9.51 ± 8.83 -
Intensity (NRS) 4.13 ± 1.61 6.29 ± 2.10 -
Values are expressed as mean ± standard deviation
TTH tension-type headache, NRS numeric rating scale, NS non-significant

oVEMP abnormalities
Eight patients in the migraine group (7, 18.4 % unilateral; 1, 2.6 % bilateral) demonstrated absent oVEMP responses, while responses could not be obtained for three patients in the TTH group (2, 6.7 % unilateral; 1, 3.3 % bilateral) and five patients in the control group (3, 6.0 % unilateral; 2, 4.0 % bilateral). A low response rate was observed in migraineurs, but no statistical difference was detected in the response rate of oVEMP among groups (Table 2). In oVEMP, the migraine group had mean latencies of bilateral n1 and left p1 significantly longer than the other groups (p < 0.05). Mean amplitudes of n1-p1 were lower than in the other groups, but the difference did not reach statistical significance (Table 3). No significant difference was observed in the AR amplitude or interaural latency differences of oVEMP. Illustrated examples of oVEMP tracings in controls and patients with migraine are shown in Fig. 1. Box plots of statistically significant oVEMP parameters are shown in Fig. 2.
Table 2 VEMP response rates in headache patients and healthy controls
TTH (n = 30) Migraine (n = 38) Controls (n = 50)
oVEMP
Bilateral response, n (%) 27 (90.0 %) 30 (78.9 %) 45 (90.0 %)
Unilateral response, n (%) 2 (6.7 %) 7 (18.4 %) 3 (6.0 %)
No response, n (%) 1 (3.3 %) 1 (2.6 %) 2 (4.0 %)
cVEMP
Bilateral response, n (%) 23 (76.7 %) 34 (89.5 %) 46 (92.0 %)
Unilateral response, n (%) 7 (23.3 %) 4 (10.5 %) 3 (6.0 %)
No response, n (%) 0 (0 %) 0 (0 %) 1 (2.0 %)
TTH tension-type headache, oVEMP ocular vestibular evoked myogenic potential, cVEMP cervical vestibular evoked myogenic potential
Table 3 oVEMP results of headache patients and healthy controls
Parameters TTH Migraine Controls
Left side
latency n1 (ms) 11.29 ± 0.78** 12.34 ± 1.43*,** 11.29 ± 0.73*
latency p1 (ms) 16.09 ± 0.83 17.05 ± 1.95* 16.11 ± 0.82*
n1-p1 interpeak latency (ms) 4.79 ± 0.87 4.75 ± 1.22 4.82 ± 0.92
n1-p1 amplitude 11.64 ± 6.73 8.00 ± 5.21+ 11.66 ± 9.14
Right side
latency n1 (ms) 11.42 ± 0.86** 12.41 ± 1.41*,** 11.58 ± 0.90*
latency p1 (ms) 16.41 ± 0.89 16.99 ± 2.02 16.20 ± 1.04
n1-p1 interpeak latency (ms) 4.99 ± 1.02 4.58 ± 1.24 4.62 ± 1.00
n1-p1 amplitude 11.29 ± 6.77 7.51 ± 4.47+ 11.76 ± 10.79
Interside difference
interaural latency diff., n1 0.64 ± 0.86 0.91 ± 0.97 0.74 ± 0.72
interaural latency diff., p1 0.64 ± 0.55 0.84 ± 0.95 0.78 ± 0.62
amp. asymmetry ratio, n1 0.23 ± 0.17 0.28 ± 0.17 0.23 ± 0.16
amp. asymmetry ratio, n1 0.22 ± 0.19 0.28 ± 0.21 0.24 ± 0.15
*p < 0.05, statistically significant between patients with migraine and controls; **p < 0.05, statistically significant between patients with migraine and patients with TTH; values are expressed as the means ± standard deviation
TTH tension-type headache, oVEMP ocular vestibular-evoked myogenic potential, amp amplitude
Fig. 1 oVEMP and rectified cVEMP responses in normal subjects (a-1, b-1, respectively) and migraine patients (a-2, b-2, respectively). oVEMP: ocular vestibular evoked myogenic potential; cVEMP: cervical vestibular evoked myogenic potential
Fig. 2 Box plots of latency of oVEMP. Latencies of a left n1, b left p1, and c right n1. Horizontal dashed lines indicate the grand average. *p < 0.05, statistically significant difference between migraine patients and healthy controls; † p < 0.05, statistically significant difference between migraine patients and patients with TTH; oVEMP: ocular vestibular evoked myogenic potential

cVEMP abnormalities
Four patients in the migraine group (4, 10.5 % unilateral; 0, 0 % bilateral), seven patients in the TTH group (7, 23.3 % unilateral; 0, 0 % bilateral) and four patients (3, 6.0 % unilateral; 1, 2.0 % bilateral) in the control group showed absent cVEMP responses. There was no statistically significant difference among the groups with respect to cVEMP response rate (Table 2). Illustrated examples of rectified cVEMP tracings in controls and patients with migraine are shown in Fig. 1. Additionally, p13 and n23 latencies and rectified amplitudes of cVEMP in migraine without aura and TTH patients did not differ significantly from those of healthy controls (Table 4). Moreover, no significant difference was observed in the amplitude AR or interaural latency differences of cVEMP.
Table 4 Rectified cVEMP results of headache patients and controls
Parameters TTH Migraine Controls  P value
Left side
latency p13 (ms) 12.78 ± 1.37 13.57 ± 2.37 12.84 ± 1.81 NS
latency n23 (ms) 20.82 ± 2.01 21.98 ± 3.01 21.32 ± 2.06 NS
p13 rectified amp (μV) 42.43 ± 19.10 38.61 ± 24.95 39.41 ± 21.81 NS
n23 rectified amp (μV) 53.22 ± 13.90 58.52 ± 37.73 50.95 ± 34.25 NS
Right side
latency p13 (ms) 12.89 ± 2.45 13.68 ± 2.16 13.01 ± 2.00 NS
latency n23 (ms) 21.06 ± 2.17 22.09 ± 3.10 21.56 ± 2.29 NS
p13 rectified amp (μV) 38.97 ± 21.05 34.49 ± 23.40 41.79 ± 25.55 NS
n23 rectified amp (μV) 49.98 ± 15.70 46.38 ± 28.37 57.79 ± 39.72 NS
Values are expressed as the means ± standard deviation
TTH tension-type headache, cVEMP cervical vestibular evoked myogenic potential, amp amplitude, NS non-significant