Preoperative computerized dynamic posturography as a prognostic indicator of balance function in patients with acoustic neuroma.

Abstract

We conducted a study to determine the prognostic reliability of preoperative computerized dynamic posturography (CDP) in patients undergoing surgical excision of an acoustic neuroma. Our goal was to determine the correlation between objective preoperative assessments of balance function and subjective postoperative patient self-assessments. To that end, we retrospectively reviewed the records of 21 adults who had undergone preoperative CDP, and we subsequently obtained their subjective assessments of balance function by follow-up telephone surveys at least I year postoperatively. We conclude that although CDP has proven to be useful in many aspects of balance evaluation, it did not appear to be a valuable predictor of subjective postoperative balance function in these patients.

Introduction

Patients who are about to undergo resection of an acoustic neuroma routinely request an assessment of their prognosis prior to surgery. Many are concerned about experiencing prolonged postoperative disequilibrium. To date, no preoperative test has proven to be a valid, reliable predictor of postoperative balance function in these patients.

Computerized dynamic posturography (CDP) has become an increasingly popular modality for evaluating balance function. Most clinicians and researchers use the equipment, protocol, and normative values developed by NeuroCom International of Clackamas, Ore., as the standard for testing and comparison.

A central aspect of the CDP protocol is the sensory organization test (SOT), which is the focus of much current research. The SOT helps the physician evaluate how visual, somatosensory, and vestibular inputs affect a patient's ability to maintain functional balance. This objective test measures the extent of a patient's sway while standing on a force platform during six conditions:

* Condition 1 is a simulation of a common, normal state. With eyes open, the patient stands on a fixed platform amid a fixed visual surround.

* In condition 2, the platform and visual surround are both still fixed, but the patient's eyes are shut.

* In condition 3, the eyes are open and the platform is fixed, but the visual surround tilts in the direction of the patient's sway, thereby delivering inaccurate visual information about orientation in space.

* Conditions 4, 5, and 6 are the same as conditions 1, 2, and 3, respectively, except that the platform moves. The sway-referenced platform tilts with the patient's sway, thereby altering somatosensory input. As a result, conditions 5 and 6 effectively force a patient to rely on vestibular inputs alone to maintain balance.

In this article, we describe our study of the reliability of preoperative CDP as a prognostic indicator of postoperative balance function in patients with acoustic neuroma. We chose subjective patient self-reports of postoperative balance function as an outcome measure because this information represents a direct assessment of how patients feel about an issue that is of primary interest to them during preoperative counseling.

Patients and methods

Twenty-one patients--8 men and 13 women, aged 30 to 71 years (mean: 53.6)--were evaluated by CDP prior to surgical removal of an acoustic neuroma. They were the first 21 patients to undergo CDP after the equipment had been acquired by the senior author (R.T.S.). The test was ordered for all patients regardless of whether or not they had expressed any preoperative complaint of dysequilibrium. The NeuroCom EquiTest equipment, protocol, and standards were used, and SOT results were analyzed for each patient. At surgery, 20 patients underwent tumor removal via a translabyrinthine approach and 1 (patient 5) via a retrosigmoid (lateral suboccipital) approach.

Subjective assessments of postoperative balance function were obtained via a telephone survey conducted no sooner than I year following surgery. The survey was conducted by the lead author (E.B.), who identified himself as a medical student working with the senior author. Patients were asked to rate their balance function on a scale of 0 to 5:

0: I have no balance problems whatsoever.

1: I feel unsteady while walking or standing.

2: I have a spinning sensation while walking or standing.

3: I fell while standing or walking because I felt off balance.

4: I am afraid to walk because I feel off balance.

5: I am wheelchair-bound because of my balance problems.

Results

Preoperatively, abnormal CDP findings were noted in 17 of the 21 patients (81.0%); SOT conditions 5 and 6 were the most troublesome (table).

We were able to contact 19 of the 21 patients during the postoperative survey (table). Findings:

* 6 patients (31.6%) rated themselves with a score of 0.

* 8 patients (42.1%) scored 1.

* 1 patient (5.3%) scored 2.

* 3 patients (15.8%) scored 3.

* 1 patient (5.3%) scored 4.

* No patient scored 5.

Of the 3 patients who reported that they had experienced a fall, 2 were at least 60 years old and 1 had had a larger (3 to 4 cm) tumor.

Discussion

Black et al studied 14 patients who had undergone unilateral vestibular surgery: 7 labyrinthectomies for Meniere's disease or endolymphatic hydrops, 4 middle fossa excisions of acoustic neuromas, and 3 vestibular nerve sections for Meniere's disease. (1) Patients were evaluated by CDP preoperatively and then at three periods ranging from 0 to 9 days, 10 to 99 days, and 100 to 999 days after surgery.

Their findings:

* Preoperatively, 5 patients (36%) exhibited CDP abnormalities during SOT conditions 5 and 6.

* At 0 to 9 days, all 14 patients (100%) exhibited abnormalities during conditions 5 and 6.

* At 10 to 99 days, 6 patients (43%) exhibited such abnormalities.

* At 100 to 999 days, only 3 patients (21%) exhibited such abnormalities.

These data show that over time, patients tended to adapt to the unilateral loss of vestibular function, and their CDP results either improved or stabilized.

Cass et al evaluated 24 patients who underwent posterior fossa vestibular nerve section for intractable vertigo caused by Meniere's disease, benign paroxysmal positional vertigo, vestibular neuritis, or perilymph fistula. (2) CDP was performed preoperatively and 1 week, 1 month, and 3 months postoperatively. Their findings:

* Preoperatively, 20 patients (83%) had abnormal preoperative CDPs.

* At 1 week postoperatively, 18 of the 24 patients were evaluated by CDP, and 8 (44%) manifested a vestibular deficit pattern with falls during SOT conditions 5 and 6.

* At 1 month, all CDP results were normal.

* However, at 3 months, 5 of the 24 patients (21%) had abnormal CDPs, including 3 whose preoperative CDPs were also abnormal.

This study showed that patients with abnormal preoperative CDPs tended to not maintain good balance function by the late postoperative follow-up.

Shepard et al studied 152 patients with varying diagnoses who were enrolled in a balance rehabilitation program. (3) They found that the results of pretherapy CDP were a reliable indicator of overall therapy outcome. Patients whose SOT patterns indicated severe vestibular dysfunction had significantly poorer posttreatment outcomes (p < 0.05).

Levine et al suggested the possibility of using preoperative CDP to determine whether acoustic neuromas smaller than 1.5 cm originate in the inferior or superior branch of the vestibular nerve. (4) In a series of 6 patients, they found that at a sway-reference gain of 1.5, patients whose neuromas originated in the inferior branch exhibited abnormalities during SOT conditions 5 and 6, whereas patients whose tumors originated in the superior branch had normal CDPs.

In our study, 81.0% of patients with acoustic neuromas had abnormal preoperative CDPs, most during SOT conditions 5 and 6. SOT conditions 5 and 6 force patients to rely on vestibular inputs for balance, even as these inputs are being compromised by the presence of their tumor. We found no correlation between the presence or severity of preoperative CDP abnormalities and postoperative balance function. Furthermore, we found no correlation between a patient's age or tumor size and postoperative balance function. The overwhelming majority of our patients scored 0 or 1 on the postoperative survey, indicating that most patients achieve and maintain adequate balance function postoperatively.

These observations are consistent with the findings of El-Kashlan et al, who used a survey to correlate preoperative symptoms with postoperative subjective balance function in 220 patients who had undergone surgical resection for acoustic neuromas. (5) They used a dizziness handicap inventory (DHI) scaled from 0 to 100, with 100 indicating the poorest balance function. The postoperative DHIs in their patients ranged from 0 to 82 (mean: 17), indicating that most patients had adequate balance function.

El-Kashlan et al also found significant correlations between postoperative balance function and several preoperative factors, including the magnitude of caloric weakness on the side of the acoustic neuroma, preoperative vestibular disability scores, abnormal positional nystagmus, abnormal vestibuloocular reflex asymmetry on rotary chair testing, and the use of postoperative vestibular habituation exercises. (5) On the other hand, they found no correlation between preoperative SOT results during CDP and various postoperative balance outcome measures.

We conclude that although CDP has proven to be useful for many aspects of balance evaluation, it does not appear to be a valuable prognostic indicator for predicting subjective postoperative balance function in patients who are about to undergo surgery for the removal of an acoustic neuroma. Although CDP probably provides an accurate reflection of the level of equilibrium problems experienced by patients, it may not reflect accurately postoperative balance function. Additional research aimed at collecting subjective and objective data from larger samples of patients should he helpful in clarifying the value of preoperative CDP in this important patient population.

Table. Patient characteristics and pre- and postoperative results

                                      Preoperative       Postoperative
                   Tumor              CDP abnormality    patient
Pt.    Age/sex     size/side          (SOT condition)    self-rating

1      54/F        3 to 4 cm/L        5, 6               0
2      56/F        1.5 cm/L           5, 6               N/A
3      68/F        2.5 cm/L           5, 6               1
4      55/F        1 to 2 cm/R        2, 3, 4, 5, 6      1
5      53/M        4 to 5 cm/R        5, 6               0
6      56/F        1.5 cm/R           5, 6               0
7      34/M        3 to 4 cm/R        5, 6               3
8      60M         3 cm/L             WNL                3
9      64/M        8 mm/R             4, 5, 6            1
10     59/F        1.2 cm/R           WNL                1
11     60/F        1.4 cm/R           3, 4, 5, 6         0
12     30/M        4 cm/L             5, 6               N/A
13     62/F        1.5 cm/R           3, 4, 5, 6         3
14     33/F        2 cm/R             6                  1
15     71/M        4 cm/L             5, 6               2
16     48/M        3 cm/L             WNL                1
17     61/F        1 cm/L             3, 4, 5, 6         4
18     51/F        3 cm/L             6                  1
19     60/F        9 mm/L             WNL                0
20     37/F        2.7 cm/R           6                  0
21     53/M        3 to 4 cm/R        3, 5, 6            1

CDP = computerized dynamic posturography; SOT = sensory
organization test; L = left; N/A = not available; R = right;
WNL = within normal limits.

References

(1.) Black FO, Shupert CL, Peterka RJ, Nashner LM. Effects of unilateral loss of vestibular function on the vestibulo-ocular reflex and postural control. Ann Otol Rhinol Laryngol 1989;98:884-9.

(2.) Cass SP, Kartush JM, Graham MD. Clinical assessment of postural stability following vestibular nerve section. Laryngoscope 1991;101: 1056-9.

(3.) Shepard NT, Telian SA, Smith-Wheelock M, Raj A. Vestibular and balance rehabilitation therapy. Ann Otol Rhinol Laryngol 1993;102(3 Pt 1):198-205.

(4.) Levine SC, Muckle RP, Anderson JH. Evaluation of patients with acoustic neuroma with dynamic posturography. Otolaryngol Head Neck Surg 1993:109(3 Pt 1):392-8.

(5.) El-Kashlan HK, Shepard NT, Arts HA, Telian SA. Disability from vestibular symptoms alter acoustic neuroma resection. Am J Otol 1998:19:104-11.

From the Department of Otolaryngology--Head and Neck Surgery, Albert Einstein College of Medicine, Bronx, N.Y. (Dr. Bergson), and the Department of Otolaryngology--Head and Neck Surgery, Thomas Jefferson University and Graduate Hospital, Philadelphia (Dr. Sataloff).

Reprint requests: Robert T. Sataloff, MD, 1721 Pine St., Philadelphia, PA 19103. Phone: [phone]; fax: [phone]; e-mail: [e-mail]