Chapter 10

“Across the board” posturography abnormalities in vestibular injury

Mallinson AI, Longridge NS.

Otol Neurotol 2005 July;26(4):695-8.

ABSTRACT

Objective: To analyze a newly defined group of Computerized Dynamic Posturography abnormalities and to determine if these patients' abnormalities are of vestibular origin.

Study Design: Analysis of results drawn from our larger study of two groups of sequentially referred patients complaining of dizziness and/or imbalance.

Setting: A tertiary and quaternary care ambulatory referral centre.

Patients: Two groups of patients were studied. One was a group of patients who had suffered work-related head trauma and had subsequent complaints of dizziness and/or imbalance. The other was a group of patients referred for dizziness and/or imbalance who had no history of head trauma, work related injury or litigation procedures.

Interventions: Standard vestibular assessment including Computerized Dynamic Posturography was carried out on all patients.

Main Outcome Measures: CDP results of all patients were reanalyzed and all results were pulled which were abnormal on at least 5 of 6 sensory conditions. All results were analyzed using a quantitative method of detecting malingering and also using our newly developed nine point subjective/objective criteria scale.

Results: While the standardized formulae categorized most of these results as “aphysiologic,” our nine-point protocol showed most of the patients to be legitimate.

Conclusions: These results represent a legitimate subgroup of vestibular patients that we feel have been more or less unrecognized, many of whom are incapacitated by imbalance and disorientation. These results also are helpful in measuring safety of these patients in the workplace.

KEYWORDS: dizziness, imbalance, posturography, vestibular.

INTRODUCTION

Traditional vestibular assessment with electronystagmography (ENG) is frequently unhelpful in localizing or even delineating a vestibular lesion, as ENG findings are often normal. Computerized Dynamic Posturography (CDP) does not provide localizing or lateralizing information, but it is a more sensitive test at detecting the presence of a vestibular system abnormality (1). It also is useful in assessing the safety of a patient at home or in the workplace, and is an appropriate technique for measuring functional ability (2).

Many patients that we see do not voice traditional complaints of vertigo, but report symptoms of vague imbalance and unsteadiness, which is very important to document and quantify especially with respect to workplace safety and also for safety in everyday activity. Occupations such as roofing, bridge building, crane operating, or even waitressing can be hazardous to the patient or surrounding people. Posturography frequently is helpful in assessing these patients, as it is very often abnormal.

Patients who have vestibular complaints frequently have abnormal CDP Sensory Organization Test (SOT) assessments, and often exhibit “typical” vestibular dysfunction patterns (e.g., “5,6 down”; “6 down”) (3), or abnormality patterns that are suggestive of a specific preference or dependence on visual or somatosensory information (e.g., “4, 5, 6 down”; “3, 5, 6 down”) (2). Many patients that we assess have CDP SOT deficits, which do not fit a traditionally recognized pattern. Not infrequently, they have deficits on 4, 5, or even all 6 of the SOT conditions. Although they relate vestibular sounding stories after careful history taking, and often have no known ulterior motives such as litigation, etc., these nonspecific SOT abnormality patterns are regarded in the literature as “aphysiologic” (2). In fact it is suggested in the CDP interpretation manual that during SOT assessment, if a generalized increase in sway is seen resulting in a patient's performance being impaired to an equal extent on all six conditions, vestibular system dysfunction as the primary cause of imbalance is unlikely.(3)

We see nonspecific CDP SOT abnormalities on a recurring basis in all three of the populations we encounter clinically; standard referrals to our tertiary care Dizzy clinic, work-injured patients who are looked after by a government-funded Worker's Compensation system, and medical-legal patients (often post- MVA) who are involved in a litigation process. We refer to these abnormality patterns as “across the board” abnormalities. We use this term when at least 5 of 6 SOT conditions are subpar. In a companion study, we assessed two groups of patients. From these two groups, we extracted a subgroup of patients, all with similar “across the board” CDP deficits. These patients had histories of unsteadiness and imbalance, and neurological assessment of them did not identify a lesion to account for their complaints. We wondered if this group of “nonspecifics” did, in fact, represent a group of patients with legitimate pathology. We felt that they warranted closer study, and we undertook to analyze their results using standardized methods of evaluating aphysiologic performance, and also by using our criteria for detecting aphysiologic behaviour reported in our companion study (4).

TABLE 1. Patients with nonspecific CDP abnormalities.

METHODS

The CDP SOT results of the 61 patients reported in our companion paper (4) were analyzed. A similar analysis was carried out on the results of the 109 patients referred to us by the Workers' Compensation Board. All of these patients had complaints of dizziness, which came on after some type of work-related head injury. All had an assessment by a neurologist, and it was felt that their complaints were not of neurological origin.

From those two groups of patients (nontrauma and trauma), a subgroup of 39 patients with CDP SOT deficits on at least 5/6 conditions (for which we have coined the term “across the board” abnormalities) was selected. There were 33/109 patients from our traumatic group (30%), and 6/61 (10%) from our nontrauma group (Table 1). All CDP results were assessed using the Goebel criteria (5), Cevette formulae (6) and our nine-point malingering criteria outlined in our companion paper (4).

We also assessed the COG alignment of our 33 “across the board” patients in our traumatic injury group recorded during CDP assessment. If a patient maintains COG near the limits of stability, only small additional displacements are required to lose balance, and we thought that perhaps this may be contributing to the generalized instability shown by these patients.

RESULTS

Three patients of the trauma group who had across the board deficits were classified as flagrant malingerers using the Goebel criteria (5) and our nine-point scale (4). All three of those patients were also classified as “aphysiological” by the Cevette formulae (6). There were no patients in our nontrauma group judged by us to be malingering (none of these patients, as far as we are aware, had any ulterior motives, and they had waited three months to be assessed in our clinic).

Of the 30 remaining patients in the trauma group, 24 were classified by the Cevette formulae as “aphysiologic,” 1 was classified as “normal,” and 5 were classified as “vestibular” (Table 1). All six patients in our nontrauma group were classified as aphysiologic. (In addition to the fact that none of these 6 patients had any ulterior motives of which we were aware, 4 of them had caloric reductions, which strongly suggests vestibular pathology.)

When we examined the COG alignment of the 30 legitimate WCB trauma “across the board” patients, there was a significant difference; 16 of them (53%) had their COG behind the center of foot support, while only 9 of the other 76 patients (12%) exhibited this tendency.

DISCUSSION

We have come to recognize a group of “inherently unstable” patients with “across the board” posturography abnormalities (at least 5/6 conditions subpar). In our nontrauma group, 10% of patients fell into this category, but this figure was 30% in our trauma group. While one might conclude that this suggests the “across the board” pattern is aphysiologic, we were struck by the fact that patients with identical abnormalities were seen in the non work-injured group, and that most patients with these abnormalities had no other signs of malingering behaviour using either the Goebel criteria or our nine-point criteria. We postulate that this particular abnormality may suggest an impairment somewhere in the balance system (either peripheral or central) not necessarily reflected as a caloric abnormality (i.e., not impairing lateral semicircular canal function). In our nontrauma group, 4 of the 6 patients with these results had a unilateral reduction, but in our head injured group, only 5 of 30 (17%) had a caloric abnormality.

Does this subset of CDP results represent a legitimate group of pathology that has gone unrecognized up until now? Our group of nontraumatic dizzy patients shows results similar to those in head injured patients, although Kisilevsky et al. (7) have inferred central pathology in people showing this combination of findings. However, they do not suggest the nature of the pathology any more specifically. They draw attention to the fact that, after a head injury, most patients do not show an acute “vestibular pattern” of CDP abnormality, but indeed show a multi-sensory deficit pattern (across the board) possibly suggestive of central pathology. The assumption of a central origin for this finding is based on information in the CDP manual (3), which suggests a central origin but makes no statistical support for this assumption. We see little, if any, central pathology in our groups of patients (and our trauma patients had all been examined by a neurologist). We wondered if in addition to “across the board” CDP abnormalities, they also had seen other standardly accepted CDP abnormalities (e.g., “4, 5, 6 down”; “3, 5, 6 down” patterns). These patterns also are said in the CDP assessment manual to be “suggestive of central nervous system pathology” (3) although it is generally accepted that these CDP abnormality patterns are standardly recognized patterns of peripheral vestibular deficits (2,8).

We speculate that the “across the board” abnormality pattern is due to a disturbance of the balance system, perhaps involving parts that are as yet clinically unmeasurable (8). Even though it is not yet possible to measure vestibular activity in the utricular macula, the saccular macula, and two of the semicircular canals, we are aware that myogenic evoked potentials do measure an acoustic response from the macula of the saccule. We assume that these structures are still capable of producing significant disease. It should be remembered that otoconia weigh substantially more than their surrounding milieu, and in a situation of acute trauma, their inertia is likely to result in trauma to the macular organs.

Several studies have examined postflight instability in returning American astronauts. Paloski et al. (9) reported “substantial decrease in postural stability on landing day” in astronauts when measured on CDP. While they didn't report SOT scores for individual conditions, their discussion referring to “disrupted postural stability” seems to suggest a non-specific performance deficit.

A study by Black et al. (10) reports further results about instability of returning astronauts and shows a subtle “across the board” deficit in two of the astronauts. Interestingly, these same two astronauts had taken part in another experiment in which they had been exposed to a post flight eccentric rotation experiment. In one of these two astronauts, ataxia was so severe that posturography could not be completed initially, and when it was, the results showed a vestibular type of deficit (5,6 down) superimposed on a subtle drop in performance on all conditions. The explanation offered in this study was that, in these two astronauts, the post flight eccentric rotation had a disruptive effect on otolithic inputs. This was in agreement with Parker et al. (11) who in 1985 stated that post flight disorientation of astronauts may be related to an “otolith reinterpretation hypothesis,” in which otolithic signals in 0G conditions suggesting falls (i.e., sudden movement of the body towards the feet) are reinterpreted as linear translations, as there is no such thing in space as a “fall”. Fries et al. (12) in 1993 also suggested that although the combination of otolithic signals to postural control is controversial, it seems that otolithic information plays an important role.

More than half of the patients in the trauma arm of our study exhibited a misalignment of weight distribution, placing their weight inappropriately behind their center of foot support on a consistent basis, and the number of malaligned patients in the across the board group was significantly higher than the rest of our group. Perhaps this malalignment contributes to the generalized destabilization seen in our “across the boards.” This rearward malalignment also has been observed by Kohen-Raz (13) in patients reporting imbalance after whiplash-type injuries, and we feel this may be another feature of otolithic disruption, perhaps leaving a patient unable to calculate earth vertical in an appropriate manner. Often these patients deny any symptoms of vertigo at all, even after direct questioning, but rather they voice complaints of “being off balance” or “feeling intoxicated.”

Davies and Luxon looked at dizziness after head injury and felt that “the variety of audiovestibular abnormalities found in head injured patients would suggest that the sensory organs of the inner ear are vulnerable” (14). They also state that, based on the high incidence of benign positional vertigo (BPV) in head injury, the otoliths are the most frequently affected structure. Otolithic debris results in the well-known symptoms of canalolithiasis, and otolithic damage in our patients could account for the CDP abnormalities seen in our patients whether or not the calorics are normal.

We postulate that our group of patients (and also the returning astronauts with similar nonspecific CDP deficits) are exhibiting the vestibulospinal correlates of otolithic deficits. Our patients may represent the “other side” of BPV, and their symptoms and CDP results may have resulted from damage to the otoliths, either traumatically or nontraumatically.

We concur with Black et al. (10) that their astronauts' CDP abnormalities are physiologic and do suggest pathology of the balance system. However, most of the patients we saw in both our study groups with this pattern of abnormality were classified by the Cevette formula as “aphysiologic.” We feel that the Cevette formulae neglect to recognize the “across the board” pathology group, a legitimate group of patients demonstrating an impairment, which can be extremely compromising to a patient's employability as well as disruptive to recreational activities.

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