Athanasios Katsarkas

Benign paroxysmal positional vertigo (BPPV): idiopathic versus post-traumatic.

Between October 1974 and August 1997 in our Dizziness Clinic (n = 15,233), 2,523 patients were found to suffer from BPPV. All patients were assessed and followed up by the author. Patients (n = 337) having other ear or neurological diseases were excluded from this retrospective study. In 1644/2186 (75.21%) patients, the type of nystagmus was clinically identified in two opposite directions of gaze in the provocative head position. These patients were divided into two groups: i) idiopathic (n = 1,490) (no apparent cause); ii) post-traumatic (n = 154) (time of onset related to accident). It was found that in the idiopathic group men were older than women; women were more affected than men (2.3:1), and in the post-traumatic group there was no age difference between men and women; women and men were equally affected (1:1). In addition: i) patients were older in the idiopathic than the post-traumatic group. ii) BPPV of the posterior (PSC) was by far more prevalent than BPPV of the horizontal semicircular canal (HSC) in both groups, although there was no difference in prevalence between the two groups. iii) Bilateral involvement was more prevalent in the post-traumatic group. iv) All bilateral cases in both groups suffered from BPPV of the PSC. It is concluded that despite similarities, these two groups differ in a number of parameters. Thus the pathophysiology and the course of idiopathic vs post-traumatic BPPV may also be different.

Dizziness in aging: a retrospective study of 1194 cases.

In the Royal Victoria Hospital dizziness clinic, 1194 of 9767 (12.22%) patients were 70 years of age or older on the day of the first visit. There were 750 women and 444 men, with no difference in age distribution (p > 0.9). In 367 (27.04%) cases (percentages given as “cases” refer to the number of diagnoses [N = 1357], not the number of patients [N = 1194]), the symptoms were nonspecific, and the diagnosis was uncertain. In 530 (39.13%) patients, paroxysmal positional vertigo was either confirmed or strongly suspected. In the 241 of 254 (94.88%) confirmed cases, the observed paroxysmal nystagmus was compatible with excitation of the posterior semicircular canal. In 119 (8.77%) patients, the dizziness could not be attributed to neurologic or vestibular disease. Menieres disease, vestibular neuronitis, vascular episodes, and tumors were next in prevalence. The following conclusions were reached: (1) although no difference was found in age distribution between women and men, dizziness was more prevalent among women, which may be because of the higher survival rate of women; (2) the prevalence of paroxysmal positional vertigo was high, with apparent Involvement of the posterior semicircular canal in most cases (It is strongly suspected that paroxysmal positional vertigo is frequently misdiagnosed as vascular disease in advanced age); and (3) multisensory deficits, drugs, or systemic diseases, common in the elderly, may cause dizziness. Syndromes affecting the vestibular function, however, may be more prevalent in advanced age than is generally estimated.

The vomeronasal organ is not involved in the perception of endogenous odors

Chemosensory‐based communication is a vital signaling tool in most species, and evidence has recently emerged in support of the notion that humans also use social chemosignals (so‐called pheromones) to communicate. An ongoing controversy does exist, however, concerning the receptor organ through which these chemicals are processed. There is a widespread belief that the vomeronasal organ (VNO) is responsible for processing social chemosignals in humans. Here we demonstrate that functional occlusion of the VNO does not change the percept of, sensitivity toward, or functional neuronal processing of a putative human pheromone. Perithreshold and suprathreshold perception of the endogenous chemical androstadienone (AND) were compared, as were positron emission tomography brain activations evoked by AND when the VNO was either occluded or left open. In addition, we compared sensitivity to AND in subjects with an identifiable VNO to those in whom no VNO could be detected. Thus we could examine the effects of the VNO at several different levels of processing. Occlusion or absence of the VNO did not affect either the perceptual measurements or the functional processing of the putative human pheromone, AND. These results provide strong evidence that the human VNO has no obvious function. Pheromonal communication in humans may be conveyed via the main olfactory system. Hum Brain Mapp, 2011.

Hearing Loss and Vestibular Dysfunction in Meniere's Disease

In a retrospective study of 475 patients suffering from Menieres disease, the hearing loss, both in the low and high frequencies, and the loss of vestibular function were studied over time. There were large variations of hearing loss from case to case but, overall, the low were more affected than the high frequencies, regardless of time elapsed since onset of disease. Hearing deteriorated over time and mean values of hearing loss correlated well with the elapsed time since onset of disease. There were also large variations of post-caloric labyrinthine preponderance (lp) from case to case but, overall, lp deteriorated with time. Mean values of lp, however, did not correlate that well with elapsed time since onset of disease as the hearing loss did. Nor was there any correlation over time between level of hearing loss and lp. It is concluded that in Menieres disease the hearing, deteriorating over time, is mainly but not necessarily worse in the low frequencies; lp, indicating loss of vestibular function, does not correlate with level of hearing loss in most cases.

Modelling non-linearities in the vestibulo-ocular reflex (VOR) after unilateral or bilateral loss of peripheral vestibular function

Abstract. We recorded the vestibulo-ocular reflex (VOR) in 18 normal subjects, 50 patients with unilateral loss of vestibular function and 18 patients with bilateral loss of vestibular function. The unilateral cases had either partial loss (i.e. vestibular neuronitis or Menieres disease) or total loss (i.e. vestibular nerve section), whereas bilateral cases had only partial loss (i.e. due to ototoxicity or to suspected microangiopathy, secondary to severe kidney disease). Tests were performed at 1/6-Hz passive head rotation in the dark, with peak head velocities ranging from 125 to 190°/s. We report on the distinct VOR non-linearities observed in unilateral versus bilateral patients: whereas unilateral patients all exhibit an asymmetric hypofunction with decreasing VOR gain at higher head velocities, bilateral patients have a more severe but symmetric hypofunction associated with increasing VOR gain at higher head velocities. We present a model study that can duplicate the nature of these characteristics, based mainly on peripheral non-linear semicircular canal characteristics and secondary central compensation. Theoretical analyses point to the importance of clinical test parameters (rotation speed and frequency) in the determination of a functional VOR and the detection of reflex non-linearities, so that test protocols can seriously bias the evaluation of adequate functional recovery.

Head-shaking Nystagmus (HSN): the Theoretical Explanation and the Experimental Proof

Head-shaking nystagmus (HSN) is induced by oscillating the head at high frequency in the horizontal plane. This test is used in the clinic to detect the presence of a unilateral loss of vestibular function. HSN has been described as monophasic with fast-phase direction towards either side, or biphasic with the direction of fast phases reversing after a few seconds. Loss of vestibular function amplifies existing non-linearities in the vestibular system, so that imposed sinusoids can induce biases which are the source of HSN. Fifty-one patients suffering from loss of peripheral vestibular function (43 partial, 11 total unilateral tests) were exposed to whole-body sinusoidal stimulation, with increasing head velocities (90-220°/s) at 1/6Hz, to explore the consistency of per-rotatory induced biases. A bias was induced in all cases, but it wandered on either side, healthy or pathologic, unless test head velocities were larger than ~180°/s. Given this condition, the slow-phase bias was located towards the pathologic side for all patients with significant bias (>5°/s). These observations demonstrate that the sign and amplitude of the bias is variable and is not correlated with the lesioned side, unless high head velocities are imposed. This explains why the direction of the initial phase of HSN in the clinic seems so labile. Subsequent monophasic or biphasic characteristics of HSN are simply the reflection of interactions between two main time constants associated with ?velocity storage? and ?gaze holding? in the vestibular central processes.

Electronystagmographic (ENG) Findings in Paroxysmal Positional Vertigo (PPV) as a Sign of Vestibular Dysfunction

In 285 patients, the observed nystagmus during episodes of PPV was compatible with excitation of the posterior semicircular canal. In these cases, divided in two groups, routine ENG recordings were retrospectively reviewed. In Group A (n = 241), the ENG was performed during the time the vertigo could be elicited; in Group B (n = 44), during the time it could not. In Group A: 1) the velocity of positional nystagmus (not the paroxysmal) was less than 6 degrees/s in 93% of cases; 2) there was no statistical difference of positional nystagmus and post-caloric preponderance of opposite directions, with 66% of cases having symmetrical responses; 3) the velocity of positional nystagmus and the post-caloric preponderance were higher than in Group B. It is concluded that: (i) in most cases no concomitant vestibular dysfunction could be detected; (ii) there was a tendency to restore right-left asymmetricity when the episodes subsided; (iii) ENG recordings were not pathognomonic and did not localize the affected side; (iv) there were ENG findings suggestive of concomitant involvement of other vestibular sensors (canals), in a small number of cases.

Vestibulo-ocular Reflex (VOR) Biases in Normal Subjects and Patients with Compensated Vestibular Loss

The properties of the vestibulo-ocular reflex (VOR) were examined during sinusoidal passive head rotation in the dark at 1/6 Hz, in 9 normal subjects and 14 unilateral vestibular patients. Rotation speeds ranged from 90 to 180 degrees/s. The bias (offset of slow-phase velocity from zero) and gain in the VOR were estimated by using a polynomial (cubic) fit between head and slow-phase eye velocity, thereby allowing for possible non-linearities in the reflex. The gain in the VOR in this context refers to the linear components of the fit, and so predicts sensitivity only at low head velocities. The aim of the study was to verify previous theoretical predictions that VOR bias could vary with the rotation parameters, that this bias could be used to detect the side of a vestibular lesion even at low frequency rotation, and make non-linearities more obvious. Confirming these predictions, the VOR bias in a given test is never equal to any spontaneous nystagmus, even if present before rotation. The range of values for the gain in the VOR (as defined above) in normals and compensated unilateral vestibular patients overlap, so that they cannot be statistically separated into two response sets.(ABSTRACT TRUNCATED AT 250 WORDS)

Does the vestibulo-ocular reflex (VOR) merit redefinition?

The VOR has historically been described by parameters of the slow phase of nystagmus while fast phases have been systematically ignored. However, ample neurophysiologic and theoretical evidence suggests that fast phases are an integral part of the VOR and are not to be discarded in evaluation of vestibular function. In a series of experiments, normal subjects and compensated patients with total or partial loss of unilateral peripheral vestibular function were tested. They were exposed to sinusoidal oscillations (20, 60, and 120/second at 1/6 Hz and 25/second at 1 Hz) with no actual or imaginary visual targets (doing mental arithmetic) and the usual slow-phase parameters (gain, phase, etc.) were computed. The gaze (total eye position, slow and fast phase of nystagmus vs. head + head position in space) was also plotted vs. head position in space. It was found that in patients, fast phases of nystagmus are unequally (right vs. left) produced, extending the linear range of VOR function. It was also found that in normal subjects and patients, gaze essentially tracks the head in the absence of visual targets. It is concluded that fast phases of nystagmus contribute to gaze control during head rotations in darkness and that the definition and the testing of the VOR have to be modified to accommodate these observations.

Caloric and Rotational Testing: Merits, Pitfalls and Myths

Objectives: The evaluation of the caloric and the rotational tests in the light of contemporary data on the function and dysfunction of the vestibular system. This is attempted by using novel engineering system notions. Material and Patients: Our work in mathematical modeling of the vestibuloocular reflex. In addition, our data from thousands of patients submitted to caloric testing and more than one hundred patients submitted to rotational testing. Methods: Analysis of results in light of system engineering notions. Results and Conclusions: The caloric test, corresponding to low head velocity and movement frequency, is an excellent test in defining the degree of excitability of one side versus the other. If there is a bilateral loss of vestibular function both, right and left, caloric responses will be compromised. However, the definition of the dynamic condition of the system and the detection of nonlinearities, especially in the presence of pathology, require rotational tests, which will yield such information if data are appropriately processed. Present day knowledge is insufficient on: (1) the functional contribution of the fast phase of nystagmus, (2) the synergistic effects of semicircular canals and otoliths, and (3) the synergistic effects of vestibular and other sensory modalities.