You are not logged in.

  




Assessment and Management of Neurological Unilateral Spatial Inattention/Neglect Syndrome

Hannu Laukkanen, OD, MEd, FAAO

Emily McCart, OD

College of Optometry, Pacific University

2043 College Way

Forest Grove, OR 97116

 

Contents

 

Introduction

Unilateral spatial inattention, also known as spatial neglect, is a condition typically associated with brain injury. Patients with this condition have reduced awareness of one hemifield, usually on the side contralateral to the lesion or injury. Unilateral spatial inattention/ neglect (USI/N) is commonly the result of traumatic or acquired brain injury (e.g., a stroke) and can be quite variable in its presentation and severity. USI/N typically requires an extensive battery of tests to confirm its presence or absence and thus is often not identified by care providers. This lack of recognition can leave USI/N patients underserved with respect to their visual needs.

In this course, we will review some of the common definitions, causes, classifications, rates of occurrence, and manifestations of USI/N. We will also review some of the more common procedures used to detect and diagnose and treat the condition, and will discuss the clinical prognosis for USI/N patients.

 

Unilateral Spatial Inattention/Neglect

Remember when Joe Smith came into your office last week? He was fairly normal looking, although if you really looked closely, his hair was slightly messy on the left side and his beard wasn’t quite as well kept on the left side. He seemed to have a slight head turn with a gaze slightly to the right of center. This gaze shift was so slight that you hardly even noticed it and didn’t really give it a second thought.

You also barely noticed that as he walked down the hallway to the exam room he tended to walk a little closer to the left wall, and even caught a door knob, in passing, with his coat on the left side. During the case history his wife happened to mention that he has been hugging the center line of the road when he drives, and has almost crossed into the oncoming traffic a couple of times recently. She also noted that it seems to startle him when a car passes him on the left side and that he hasn’t been using his left turn signal or left side mirror as much as he used to. One other thing Mrs. Smith mentioned (she liked to talk) was that he had recently been leaving a little bit of food on the left side of his plate, even though he used to always clear his plate completely.

Mr. Smith admitted to feeling slightly “unsteady” recently, although he couldn’t quite put his finger on what it was and thought maybe it was just an “aging thing.”

While checking his acuities, Mr. Smith seemed to consistently miss the beginning VA letter on every line, but your projector makes the letters not quite as clear on the sides so you didn’t think much of it. Mr. Smith also didn’t follow the bead quite as far to the left when you were evaluating his extraocular muscles. However, when you ran the Frequency Doubling Technology perimetry screener on Mr. Smith, there was no field loss noted. At the end of the exam, you told Mr. Smith that you were changing his glasses prescription slightly and that his eyes were healthy - and that was the end of that.

Maybe, but things might have been different and you might have been able to make a big difference in Mr. Smith’s life if you had realized that all of the symptoms mentioned above could have been associated with USI/N. Even though none of his other health care providers had picked it up, you were in a position to detect the condition and if you had put all of this together and sent Mr. Smith for an MRI, a recent minor stroke in the posterior parietal lobe might have been diagnosed.

Definition of USI/N

Although USI/N can occur in mild forms, in its complete manifestation USI/N is a phenomenon in which an entire hemifield (generally the left) is ignored, and the “patient fails to report, respond or orient to novel or meaningful stimuli presented to the side opposite of the brain lesion.”(1) The patient acts as if a hemianopia were present, however he or she is unaware of the defect.

 

Figure 1. Visual representation of USI; the lighter shaded area represents the affected portion of the patient’s body (including the left half of the face not shown in the picture) and space.

 

Causes of USI/N

USI/N may be present after various types of unilateral brain damage. It can be seen after traumatic brain injury (TBI) or acquired brain injury (ABI). The most common cause of TBI is motor vehicle accidents. Other causes include assault, accidents in the home or workplace, and sports injuries.(2)

ABIs can be caused by cerebrovascular accidents (CVAs) such as stroke. USI/N is seen more commonly after stroke, particularly when the middle cerebral artery is involved.(3,4) USI/N can occur after left brain damage (LBD), but it is typically more frequent, more severe, and longer lasting after right brain damage (RBD).(3,5)

Unilateral spatial inattention/neglect can occur following a lesion to any of the following areas: posterior parietal cortex, frontal lobe, cingulate gyrus, thalamus, and striatum.(6) These areas are located throughout the brain, but they all play important roles in attention.

USI/N is most frequently seen after insult to the right inferior parietal lobe, also identified as the posterior parietal lobe. This area of the brain seems to play a large role in representation of personal space or body image, and external space.(3) More specifically, research suggests that the posterior parietal area is responsible for spatial localization, directing attention during voluntary and tactile tasks, and for visual awareness.(7) It is believed that the area receives and integrates incoming sensory input and produces a spatial representation of the world relative to the self.(7) The posterior parietal lobe integrates converging information from visual, auditory and vestibular areas and has extensive interconnections with the premotor cortex, the frontal eye fields, the superior colliculus, and the paralimbic areas (the strongest connections being with the cingulate gyrus).(6)

 

Researchers tend to associate deficits with a lesion in just one area, but Mesulam (8-10) believes this to be a mistake in the case of USI/N. He believes that USI/N behaviors are not a product of one specific area of the brain but are due to failures within the many interconnections between parts of the brain.

 

Figure 2. MRI scans of a patient with USI/N. The red region shows the area of the brain that was damaged. Image from http://www.sph.sc.edu/comd/rorden/neglect.html

 

Rate of USI/N Occurrence

Estimates of USI/N occurrence rates vary greatly in the literature. Stone, et al., (11) reported that over 80% of patients demonstrate USI/N following a right cerebrovascular accident, whereas Denes, et al., (12) reported only a 17% occurrence rate following a right CVA.

There is agreement in the literature, however, about the fact that USI/N is more likely to occur following lesions in the right hemisphere (potentially causing left spatial inattention) versus the left hemisphere (potentially causing right spatial inattention). Allegri (13) found that between 31% and 46% of right hemisphere stroke patients exhibited USI/N whereas only 2% to 12% of left hemisphere stroke patients showed evidence of USI/N. As measured during neuropsychological testing, left USI/N is commonly more severe than right USI/N (12), and larger lesions increase the severity of USI/N.(6)

USI/N appears to occur more frequently following stroke than following a TBI, (3) however exact numbers comparing the incidence of USI/N in stroke patients versus TBI patients are difficult to find.

Discrepancies in USI/N Diagnosis Rates

One reason for discrepancies in the rate of USI/N occurrence found in the literature could be the method of testing used to determine whether USI/N was present or not. Hier, et al., (14) studied the same group of patients and found a diagnosis rate of 46% based on behavioral observations of USI/N and an 88% diagnosis rate based on the paper and pencil Figure Copying Test. Another study (15) found a difference in diagnosis rates of between 49% on a letter cancellation test and 30% using Albert’s Test, which is a line cancellation procedure.

Another reason for the wide range of reported diagnosis rates could relate to selection criteria used in different studies and exclusion of patients who could not complete certain tasks required for some studies. An additional thing to keep in mind when comparing incidence rate data is the wide range in sample sizes used in different studies; many studies only recruited very small samples. For example, one study that Bowen, et al., (5) considered found a USI/N occurrence rate of 100% in RBD patients, but only 9 RBD patients were involved in the study.

Implications of USI/N for Daily Living

USI/N can be very debilitating for patients. There are many different manifestations of the condition and possibly even different forms of USI/N. There is also a wide range in severity seen in USI/N patients. In a severe case, the patient could lie in bed with eyes and head rotated toward the side ipsilateral to the lesion, unable to attend to the contralateral side even when spoken to from that side.(3) In other cases, such as the one described in the introduction to this course, only mild symptoms are manifest.

Many varying problems can occur in day-to-day living skills for USI/N patients. For example, he or she might be not pick up food from the side of the plate contralateral to the lesion, or might not brush hair, apply makeup, or shave on the side of the face contralateral to the lesion.

Even if USI/N begins to resolve, it can still be a very disabling condition. For example, if patients go out on a busy street many possible dangers exist if they are unaware of objects, people, or traffic on their left side.

Patients with USI/N can vary in the degree of awareness of their defect. Suchoff (7) proposes that a continuum exists ranging from no neglect (basic hemianopia with total awareness of the field cut) to complete neglect (USI/N with complete unawareness of the field cut). Patients can fall anywhere along this continuum.

Midline Shift

It is believed that patients with USI/N experience a shift in their perception of “straight ahead” or their egocentric localization so that the subjective perception of straight ahead does not correspond to the patient's objective midline. This creates a “spatial mismatch between their subjective and objective visual spaces.”(7) Karnath provided the first scientific demonstration of this phenomenon and found that the midline shift can be 15-degrees or more.(7)

Patients with large midline shifts tend to report feeling “unsteady,” “out of synch with the world,” and “not grounded.”(7) Symptoms associated with midline shift syndrome can include the following:

Extinction

Extinction is a phenomenon seen with many mild USI/N patients (or a step in the USI/N recovery process, or possibly even a sub-type of USI/N). It is a condition in which patients are capable of distinguishing a contralesional stimulus when it is presented alone but are unable to detect the same stimulus when competing stimuli are simultaneously present in the patient’s ipsilesional (and presumably intact) field.(16) This behavior is referred to as extinction because the competing ipsilesional stimulus appears to extinguish perception of the contralesional stimulus.(16) Extinction often becomes apparent when double stimulus presentation confrontational fields are done with the patient.

 

Categories of USI/N

Swan (6) has identified three different categories of unilateral spatial inattention. They are:

Memory and Representational Deficits

The category of memory and representational deficits describes a condition in which USI/N extends to visual memory and imagery of space in patients’ minds. Bisiach, et al., (17,18) described the condition in two patients with lesions in the right temporo-parietal region, and consequently left USI/N. They were asked to describe, from memory, a familiar square containing a cathedral, palaces, and shops. The patients were asked to imagine themselves facing the cathedral.

Both patients accurately described the right side of the square, but left out many things on the left side. They were then asked to imagine themselves facing away from the cathedral, and this time they were able to accurately describe what was previously on their left. But, they omitted landmarks on the other side of the square that they had recalled perfectly when oriented the other direction.(17,18)

This study suggests that memories of extra-personal space are stored in relation to one’s own self-location in that space. This study shows that USI/N is not limited to motor and sensory deficits and that it extends to behavioral aspects of brain function.(6)

Motor Neglect

Motor neglect is not a deficiency of the motor pathway; instead it refers to an inability or failure to move in space contralateral to the damaged hemisphere.(6) Motor neglect can manifest with respect to any part of an individual’s body.

Swan references a study by Watson, et al., (19) in which five monkeys were trained to open a door to their right after left leg stimulation and to open a door to their left following right leg stimulation. The monkeys were then surgically given unilateral lesions in the frontal arcuate gyrus or the intralaminar nucleus of the thalamus and the mesencephalic reticular formation. Lesions were placed in either the right or left hemisphere of the monkeys’ brains.

Following surgery the monkeys demonstrated USI/N. None of the monkeys were afflicted with limb weakness. The monkeys were then retested on the door-opening task and showed mistakes when the stimulus was presented to the ipsilesional limb (failure to open the door on the side contralateral to the brain lesion). However, when the stimulus was applied to the contralesional limb, no mistakes were made. This demonstrated that the monkeys were able to make motor responses following a sensory stimulus, but with decreased motor responses in contralateral space after sensory stimulation of the ipsilesional limb.

Sensory Neglect

Sensory neglect is a decreased or lack of awareness of sensory stimulation in contralesional space, which occurs in spite of intact primary sensory cortical areas and sensory pathways. (6) This corresponds to the observation that following right hemisphere lesions, patients with USI/N fail to attend to left hemispace (the field beginning at the body’s midline and extending laterally to individual's the left). Swan (6) states that over time these observations have led to the following conclusion: “in an individual with no known neurological pathology or impairments, the right hemisphere of the brain attends to both the right and left hemispace while the left hemisphere attends primarily to the right hemispace. Following a right hemisphere lesion, attention is directed primarily to the right hemispace, resulting in a neglect of the left hemispace. A lesion of the left hemisphere does not usually result in USN [unilateral spatial neglect] because the intact right hemisphere can direct attention to both hemispaces.”

 

Dysfunctions in Personal Space, Extra-Personal Space, and Peri-Personal Space

Stein has proposed a different system for categorizing USI/N.(20) He believes that there are two general categories. The first involves somatic dysfunctions and includes impaired tactile perception and denial of the existence of the contralesional side of the body. These are dysfunctions in personal space.

The second category involves dysfunctions of visual motor control, visual localization, and impaired visual representation of the outside world. These are dysfunctions in extra-personal space. He further subdivides this category into dysfunctions in peri-personal space.(20)

Suchoff and Ciuffreda (3) believe that initially the most obvious manifestations of USI/N occur in personal space and then proceed to dysfunctions in peri-personal space. They give examples of dysfunctions seen in each of the above categories. Personal space USI/N behaviors can include:

Peri-personal space behaviors can include:

Extra-personal space behaviors can include an unawareness or inattention to one side of the external world.

USI/N has many different manifestations and categories. It can have very negative implications for daily living affecting personal, peri-personal, and extra-personal spaces. To assist in understanding the effects of USI/N, we have created a graphical representation of the Suchoff and Ciuffreda model.

 

 

 

Figure 3. Diagrams showing effects of USI/N.

 

How is USI/N Diagnosed?

There is a wide range of tests that can be used to help detect USI/N. The most popular are “pen and paper” tests, which include line bisection, cancellation, copying, and drawing tasks.(21)

One of the more popular test batteries is the Behavioral Inattention Test (BIT). It consists of six pencil-and-paper tests (line crossing, letter and star cancellation, figure and shape copying, line bisection and representational drawing), and nine ‘behavioral’ tests.(22)

When considering the accuracy of USI/N tests, factors such as test sensitivity and specificity should be kept in mind. Misdiagnosis is minimized by using a test with high sensitivity and high specificity because it will generate fewer false negatives and less false-positives.

Line Bisection Test

The Line Bisection Test, which is part of the BIT battery, is a common USI/N assessment tool. It simply requires the patient to determine the mid-point of a horizontal line. The line is presented on a piece of paper centered with respect to the patient’s midline. The patient is asked to mark or indicate the exact middle of the line.(23) The test is scored by measuring the deviation from the patient's perceived midpoint to the true center of the line. A deviation toward the ipsilateral side of the lesion is usually indicative of USI/N. For example, a patient with a right parietal lobe lesion would bisect the line more toward the right of the center. The deviation from the true midpoint of the line can depend on the extent or severity of the patient's USI/N.

One of the problems associated with the line bisection test is that there are many different versions of it and the different versions are not standardized.(24) Some investigators also feel that other factors, such as hemianopia, might influence the results of this test. One study found that the line bisection test missed 40% of USI/N patients.(25) However, test-retest reliability was found to be 0.97 using an intra-class correlation coefficient (ICC). This indicates good reliability for the test. (26, 27)

 

Figure 4. Line Bisection Test results. Left line shows normal subject performance; right line shows perceived midpoint for a patient with USI/N caused by a right brain lesion.

 

Cancellation Tests

Cancellation tests involve visual search skills and possibly figure-ground perceptional skills also. In a cancellation test, the patient searches a page of print for specific stimuli (e.g., letters) and crosses them out as they are found.(23) Patients with USI/N have a tendency to miss stimuli contralateral to the side of the brain lesion. These tests are considered to be among the most sensitive pen and paper tests available.(28) Sensitivity is increased with a high number of targets and distracter items.(29)

There are a variety of different cancellation tests available for clinical use. Examples include the Line Crossing test, Bells test, and the Star Cancellation test.(23) A subtest of the BIT battery, the Star Cancellation test has been shown to be the most sensitive part of the battery.(21) The test consists of a page printed with 56 small stars, 52 large stars, 13 letters, and 10 short words. The goal of this test is to have the patient locate and cross out all of the small stars.(21)

The Star Cancellation test has good potential for high sensitivity because of the presence of distracter items as well as the high target density. Bailey, et al., (26) found an intra-class correlation coefficient of 0.89, indicating good repeatability. This was corroborated by another study, which found that the Star Cancellation test had a diagnostic sensitivity of 80% and a diagnostic specificity of 91%.(30)

 

Figure 5. Star Cancellation Test. Image from http://www.undergrad.ahs.uwaterloo.ca/~aktse/assessment.html

 

Line Crossing Test

The Line Crossing Test, also part of the BIT battery, is sometimes confused with the line bisection test, but it is a different assessment tool. The Line Crossing test is composed of a page printed with uniform black lines in random orientations.(21) Patients are asked simply to cross out every black line on the page. Those with USI/N should make more omissions on the side contralateral to the lesion. However, one study found a sensitivity of only 23% for the Line Crossing test.(21)

 

Figure 6. Line Crossing Test. Image from http://www.undergrad.ahs.uwaterloo.ca/~aktse/assessment.html

 

Indented Paragraph Test

The Indented Paragraph test is another commonly administered part of the BIT battery. A paragraph is printed on a page with the left-most word indented on each line by a different number of spaces. The patient reads the paragraph aloud, and the examiner notes any omissions or additions as well as how long it takes to complete the task. In one study the sensitivity of this test was found to be 77%.(21)

Baking Tray Test

The Baking Tray Test can also be used to detect USI/N. For this test, the patient is asked to place "buns," which are actually wooden cubes, as evenly and symmetrically as possible on a wooden board "baking tray." Subjects with USI/N generally skew the distribution of buns in an ipsilesional direction. Bailey, et al., (26) found the test-retest reliability to be 0.87 for patients with USI/N (this indicates good reliability).

Clock Test

The Clock Test is another part of the BIT battery that can be used as a test for representational inattention.(22) There are different versions of the test, but all share the common theme of requiring that a clock face be drawn from memory. For patients with USI/N, the numbers on the clock are typically drawn or skewed towards the side of the circle ipsilateral to the brain lesion.

 

Figure 7. Clock Test performance of a USI/N patient with a right side lesion.