Disabling positional vertigo (DPV) is a rare form of a balance disorder that is characterized by constant positional vertigo and nausea (Møller et al. 1993b; Jannetta et al. 1984). The symptoms of DPV are constant and people with DPV experience a state of nausea to a disabling degree. As symptoms become more intense with changes in head position, people with DPV are most comfortable lying in bed. In addition to abnormal vestibular test results, people with DPV also exhibit signs of functional changes in the cochlear nerve resulting in subtle but distinct changes in their auditory brain stem responses (ABR). There is a prolonged interval between peaks I and III (IPL I–III) and peak II is also abnormal (Møller et al. 1993b).

MVD operations of the vestibular nerve are in use for treating DPV. Other treatments are medications with benzodiazepines such as diazepam (Valium) (Møller 1997). The results of MVD operations for DPV are similar to those of HFS and TGN (Møller et al. 1993b). The operation is more difficult because of the risk of injuring the cochlear nerve.

Studies by De Ridder et al. (2002) produced evidence that vascular compression syndromes may arise from vascular contact along the entire CNS segment of the cranial nerves and not only at the root entry zones (Obersteiner-Redlich zone). De Ridder and Møller (2010) described the results of studies that showed the correlation between the length of the centrally myelinated (oligodendrocyte) portion of the vestibular nerve and the incidence of the microvascular compression syndrome. Furthermore, decompression of the CNS segment of the vestibular nerve is effective in eliminating DPV symptoms without decompression of the root entry zone. De Ridder and colleagues interpreted this to corroborate the hypothesis that close contact with a blood vessel anywhere along the entire length of the central portion of the vestibular nerve could be associated with symptoms.

Tinnitus is hearing meaningless sounds that are not caused by a physical sound reaching the ear. In addition to hearing annoying sounds, many people with tinnitus also experience suffering or distress that often is independent of the phantom sound of tinnitus. Severe chronic tinnitus has many similarities to what has been described for chronic neuropathic pain (Møller 2014b).

Many different treatments have been studied but few have reached routine clinical use. The reason for the inconsistent success in treatment of people with tinnitus is mainly of lack of understanding of the abnormal functions that generate the phantom sounds of tinnitus and their connection to distress and suffering. It was a major progress in understanding of the pathophysiology of tinnitus when it was discovered that chronic tinnitus is rarely caused by pathologies of the ear but rather often pathologies of the nervous system.

MVD operations directed to the cochlear-vestibular nerve are one form of treatment that is in use. However, tinnitus takes a plethora of forms (Møller 2010a) and only a few people with a certain form of tinnitus benefit from MVD operations on the cochlear nerve. The form of tinnitus that can be alleviated by MVD of the cochlear nerve is associated with ABR changes similar to those that occur in people with DPV (De Ridder et al. 2007; Møller et al. 1993a). The success rate of MVD operations for tinnitus is considerably lower than those of HFS and TGN.

The pathophysiology of DPV is unknown. The fact that the symptoms of DPV can be relieved by MVD suggests that there may be similarities between the pathology of DPV and those of the other disorders that can be cured effectively by MVD (HFS, TGN, and GPN). This means that it is likely that the anatomical location of the pathology is the brain and not the vestibular organ (inner ear).

It also seems likely that activation of neuroplasticity is involved in the creation of the symptoms of DPV similar to what is the case for, for example, chronic neuropathic pain and tinnitus (Møller 2014a).

The fact that head movements trigger the symptoms indicates that they are evoked by signals from the vestibular organ in the ear. As such signals normally do not reach consciousness, it can be inferred that, in people with DPV, the signals from the balance organ are abnormally routed to reach regions of the brain that they do not typically reach. The feeling of vertigo and nausea indicates involvement of structures in the autonomic nervous system and possibly the insula. Such rerouting can occur because of unmasking of dormant synapses that connect axons from the vestibular nuclei to different regions of the brain (Møller 2014a).

Dormant synapses may become unmasked by activation of neuroplasticity. Synapses that do not conduct because of insufficient input may also become activated if the excitatory input is increased or if inhibition is decreased. This means that the rerouting of information that causes the symptoms of DPV may be caused by hyperactivity at some level of the ascending vestibular pathways. This hypothesis is supported by evidence that the symptoms of DPV can be lessened by administration of drugs of the benzodiazepine family, which are known to be GABA_A receptor agonists and thereby enhancers of inhibition.

Little is known about the pathophysiology of those forms of tinnitus where the symptoms can be relieved by MVD of the cochlear nerve. In general, studies of patients who are undergoing MVD operations for tinnitus have shown that evoked potentials that are generated by the cochlear nerve, the nuclei, and the fiber tracts of the ascending auditory pathway of the brain stem in people with incapacitating tinnitus are not significantly different from those that can be recorded from individuals with the same degree of hearing loss but no tinnitus (Møller et al. 1992a). This suggests that severe tinnitus might be the result of abnormalities in more rostral brain structures. The abnormalities that occur in people with tinnitus may not be limited to structures that are normally associated with auditory functions, but many other structures may be involved (Schlee et al. 2009, 2010; Vanneste and De Ridder 2012).

That injury to the peripheral auditory system can result in hyperactive changes in more central auditory structures was demonstrated by Gerken et al. (1991). They found that overexposure to sound (noise impairment) affects the function of central structures in the ascending auditory pathways. Earlier, Syka and colleagues showed that noise-induced hearing loss was associated with abnormalities in the function of central auditory structures (Syka and Popelar 1982). The fact that some people with tinnitus experience hyperacusis has been taken to indicate that the physiological abnormality is located at higher brain levels and that perhaps the prefrontal cortex is involved (Hazell 1990).

Rerouting of auditory information through such activation of neural plasticity may activate an ascending auditory pathway that uses the dorsal-medial thalamic auditory nucleus. This hypothesis is supported by the finding that the nonclassical ascending pathways in adults with tinnitus may be active (Møller et al. 1992b). Other studies have shown indications that sound activated the nonclassical pathways in children but normally not in adults (Møller and Rollins 2002). This route has subcortical connections to limbic structures (Eggermont 2007; Møller 2010b, 2014a) and may explain why affective signs and symptoms such as phonophobia and depression often accompany severe tinnitus. Other studies have shown evidence of increased activation of limbic structures in people with tinnitus (Lockwood et al. 1998).

Many forms of tinnitus have similarities with central neuropathic pain (Møller 2010b, c).

The process for selection of candidates for MVD of CNVII, CNV, CNIX, and CNVIII depends almost entirely on the patient’s history and assessment of the patients’ symptoms. While HFS, TGN, and GPN have distinct diagnostic characteristics, the symptoms of DPV are similar to those of several other vestibular disorders, which may not respond to MVD. It is an additional challenge to determine which side of the patient is affected by the DPV. Due to these variables, the process to select candidates for MVD operations needs to be more rigorous for potential DPV cases than for other MVD procedures. Not all people with the symptoms of DPV are candidates for MVD operations.