## 4 Discussion  
Although the otoneurological examination was found to be negative, the first interesting finding in this study was the significant decrease in vHIT scores in MCS subjects (Figure 2B) in whom DHI highlighted a prevalence of dizziness-related symptoms (Figure 1A). In turn, a significant increase in classical posturography and FFT parameters as well as in VD behaviour was found in the same group (Figure 2A). This syndrome has been classified by many authors as part of a wide group of emerging diseases--labelled idiopathic environmental intolerances (IETs)--which are characterized by symptoms attributed to environmental agents [40]. For instance, many studies have tried to find an unifying pathophysiology for all IEIs, focusing on CNS reactions to environmental stimuli, with activation changes of the brain areas related to sensory processing and emotional responses [1; 5; 41; 15; 42; 1; 1; 16; 41; 1]. Since environmental noise has been recognised as an important health quality stressor [43], relevant literature up to now has focused mainly on auditory symptoms [21; 22] without highlighting possible vestibular and postural consequences. In particular, no study protocol has found an impaired VOR function in MCS patients with vHIT. By providing a new dimension in vestibular evaluations [33], in this study the test permitted a quantitative assessment of the lateral semi-circular canal function and highlighted side and receptor specific information about the VOR [31; 32; 33], resulting in a bilateral reduction of both MCS gain and reslo (Figure 2B, Table 2). These aspects suggested that MCS patients, when compared with HC normative data, have a vestibular impairment (although not clinically evident by means of a cHIT). In line, FFT PS analysis and classical posturography parameters were demonstrated to be congruent with the above-mentioned vestibular damage in MCS. In fact, literature demonstrated body sways at the low frequency interval to be mainly under vestibular control [35; 44; 36] and patients with vestibular deficits (i.e., vestibular neuritis, Meniere's disease) have consequently increased body sways at the low frequency interval as compared with normal subjects [35; 44]. Furthermore, increased body sways within the middle interval and in classical posturography parameters especially during closed eye condition tend to confirm similar findings in previous studies, and result in a decreased ability to adapt to balance perturbations under complex conditions in certain disorders affected by a lack of vigilance [45; 46; 47; 48; 49]. It has previously been noted that the integration of information from the visual, vestibular and somatosensory receptors and motor coordination are processes requiring attention and vigilance [48], especially when information from other sensory systems is not reliable [50]. Considering the closeness between MCS and other related idiopathic disorders affected by functional postural impairment and attention and vigilance decrease (i.e., fibromyalgia, chronic fatigue syndrome) [45; 51] it could be postulated that such phenomena may lead to slower or inappropriate sensory integration [48]. In relation to this, negative correlation found between RI values and QEESI total scores further strengthen these aspects, highlighting possible negative influences between higher values on the questionnaire tool used in the study and this kind of body sway parameter. Moreover, MCS patients demonstrated an increase in VD parameters (Figure 2A, Table 2), the concept of which has been postulated by previous authors [28; 52] observing that, in conflicting circumstances between sensory modalities involved in spatial orientation, some subjects depend mainly on visual input. These visual-dependent subjects are more likely to be be bewildered by tilted or moving visual surroundings [28; 52].