Lermoyez syndrome is an infrequent disease of the auditory and vestibular system. It is likely to be caused by endolymphatic hydrops, and is defined by attacks of vertigo, together with tinnitus, aural fullness, and fluctuating hearing loss, followed by temporary hearing improvement. Surgery is considered for cases with frequent, severe episodes.
Lermoyez syndrome (LS) is generally regarded as a version of Meniere’s disease (MD), but this classification is not completely accepted and is under investigation. MD first reported in 1861 by Meniere, is usually referred to as idiopathic endolymphatic hydrops; the latter is due to increased pressure in the endolymph of the inner ear and can cause attacks of vertigo, tinnitus, and aural fullness, and result in hearing loss. Nausea and emesis also accompany the attacks. MD has several variants apart from the classic form; it can manifest without vertigo, or without hearing loss, or it can appear as Tumarkin otolithic catastrophe . LS is characterized by essentially the same symptoms as MD (and therefore is likely to be a variant of it), but with one striking difference: a temporary improvement in hearing ensues at the time of the vertigo attacks .
LS is a very rare medical entity, and consequently, the number of in-depth descriptions of the disease is small . In a study, which examined 12 patients with LS, some had hearing alterations without vertigo, while others had vertigo without alterations in hearing, indicating a similarity in the origin of LS and MD  . Another report on a patient with bilateral LS also came to the conclusion that endolymphatic hydrops was the source of the problem, based on electrocochleography measurements , although dissenting opinions have been voiced 
The attack may last for hours, with both the improvement in hearing in low frequencies during the episode and the deterioration of hearing occurring before the next attack lasting from days to months . The improvement in hearing can occur during or more commonly within a few hours following the attack . Hearing loss may be fast at the initial stages and slow down later . However, attacks of vertigo may increase in frequency as the disease progresses, as in the case of a patient with stabilized MD in one ear, and newly developed LS in the other .
Laboratory tests are routinely performed to exclude metabolic and hormonal diseases. Specific tests for LS (or for MD) have not yet been found. Magnetic resonance imaging (MRI) imaging is used for excluding anatomical abnormalities and growths, for example, acoustic neuromas. Three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) MRI is capable of quantitative evaluation of endolymphatic hydrops .
A number of acoustic exams are available for the evaluation of hearing loss and vertigo. Pure tone audiometry and acoustic impedance determine the hearing threshold and the acoustic reflex threshold; lower frequencies are usually affected more than higher ones, for example in one patient the threshold of hearing was found to increase in the range of 200-2000 hertz (Hz), whereas the values at high frequencies were relatively stable . The glycerol test, which detects an improvement in air-conductive hearing threshold following oral glycerol administration, is characteristic of both MD and LS  . Electrocochleography detects the expansion of the basilar membrane by measuring the ratio of the summing potential from the movement of the membrane and the nerve action potential following auditory stimulation. An increased value is often observed in MD and LS  . Auditory brainstem response and the caloric test, which forms part of the assessment for vestibular function, are also used .
Newer methods are also available for testing dynamic otolith and horizontal semicircular canal function. These include evaluation of utricular and saccular function  by determination of ocular and cervical vestibular evoked myogenic potentials, and assessment of the vestibulo-ocular response by using the video head impulse test .