Exam Techniques: Head Impulse Test (HIT), Nystagmus, and Test of Skew

00:01 Let's start by understanding the head impulse test.

00:04 This is a rapid and passive horizontal head rotation from the center to the lateral position when the patient is fixated at a central target.

00:14 So typically, I'll ask the patient to look at me, or look at my nose, or look at something on the midline.

00:20 With both hands on each side of the patient's face, I will induce a rapid head turn.

00:27 This is a passive head turn with the patient being as relaxed as possible.

00:31 And we'll start in the middle and go to the right, or start in the middle and go to the patient's left.

00:36 A normal head impulse test is where the patient remains fixated on the examiner.

00:42 So the patient's eyes remain fixated on me.

00:45 As the head move left, the vestibular apparatus recognizes that the brain recognizes that the head is moving left and compensatory moves the eyes right, so the patient is able to stay fixated on me.

01:00 When we go from straight to right, when we move the patient's head to the right, again, the vestibular apparatus should recognize that, and the brain should activate eye movement back to the left.

01:11 And so the eye should remain fixed on the target.

01:14 That's a normal head impulse test.

01:17 What about an abnormal head impulse test? This is where the patient again is instructed to remain fixated on the examiner at all times.

01:25 And when the head is moved, the eyes move with the head.

01:30 So when I start in the midline and move the patient's head to the left, the eyes initially move out to the left.

01:35 And then we see a corrective saccade, where the patient recognizes that they need to be looking at the examiner and induced that goal directed eye movement back to the examiner.

01:46 That would be a left sided abnormal head impulse test.

01:49 If we move the patient's head to the right, again, we may see the eyes remain fixed out to the right as the head moves, and then a corrective saccade.

01:57 It's that corrective saccade that we're looking for, that indicates an abnormal head impulse test.

02:03 This is the first of the three critical exam maneuvers that we're going to do for patients with the acute vestibular syndrome.

02:13 A normal head impulse test, a little bit paradoxically suggests that this could be a central cause of the acute vestibular syndrome.

02:21 So this is one of those tests in neurology, where a normal test is not reassuring.

02:27 And a normal head impulse test could indicate a signs of a brainstem, or cerebellar stroke, or multiple sclerosis, or one of those central causes.

02:36 Here, an abnormal head impulse test is a reassuring finding.

02:41 That reassures the examiner that the cause of this patient's vertigo and acute vestibular syndrome is likely to be of a peripheral origin.

02:50 Vestibular neuritis or labyrinthitis.

02:54 The second exam technique is to look for nystagmus.

02:58 And I can find nystagmus to be very difficult to understand, categorize, and evaluate in patients.

03:05 Let's start with a definition.

03:06 It's repetitive uncontrolled movements, where they're shaking or jerking of the eyes.

03:11 And we see many different descriptions Pendular nystagmus, optokinetic nystagmus, Jerk nystagmus, gaze-evoked nystagmus, there's a lot written about and that can be seen in patients.

03:24 When we're evaluating the acute vestibular syndrome, I would break nystagmus down into two options.

03:31 Unidirectional or bidirectional.

03:34 Into the trained eye, or even the untrained eye.

03:37 We should be able to categorize and evaluate the patient's nystagmus in one of these two ways.

03:43 So let's start with unidirectional nystagmus.

03:46 What is it? Well as you see here, whether the eyes are in primary gaze or primary position, or looking to the left or looking to the right, the fast phase of the nystagmus the jerk is always in the same direction.

04:00 So at primary position, we see jerking, the fast phase of jerking in one direction.

04:05 When the patient looks to the left, we ask the patient to follow our finger and look to the left.

04:10 Again we see that the fast phase of the nystagmus the jerk is to the same side.

04:15 And when we asked the patient to look to the right, again, we see the fast phase of the nystagmus in the same direction.

04:23 The nystagmus made jerk to the left, it made jerk to the right.

04:26 But with unidirectional nystagmus it's always in the same direction.

04:31 And this indicates peripheral pathology.

04:34 This is a reassuring finding.

04:35 Something that reassures us that this is likely not of central origin and more likely of peripheral origin.

04:42 Importantly, we often see that unidirectional nystagmus, nystagmus that is evoked by a peripheral source often follows Alexander's law.

04:52 Where the intensity and severity of the nystagmus is worse on the side of the lesion.

04:59 So when the nystagmus is worse on the right, we worry about a right sided peripheral vestibular pathology, when the status is worse on the left and a little bit better when the patient's looking to the right, we worry about a left sided peripheral vestibular pathology.

05:14 and that's Alexander's law helps us to localize the side of the peripheral vestibular syndrome.

05:22 That's different from direction changing nystagmus.

05:25 And this is the second type nystagmus we'll look for in these patients.

05:30 Direction-changing nystagmus indicates central pathology and it is exactly as it sounds.

05:36 It's nystagmus that changes directions.

05:39 We may see nystagmus in one direction at primary position, and another direction at right gaze.

05:44 In one direction with left gaze and another direction with right gaze.

05:48 It's nystagmus that changes position.

05:52 The third technique we'll look for is the test of skew.

05:55 And here we're looking for a vertical misalignment of the eye.

05:59 This is a subtle dis-conjugation of vertical dis-conjugation of the eyes.

06:05 In some patients, it can induce diplopia.

06:07 Patients may see double.

06:09 In others, it's so subtle, that the patient will only see one image.

06:14 We can see some patients compensate with a head tilt, and in others it requires provocative maneuvers to find that this vertical misalignment, and to test for a skew deviation.

06:25 There's two ways we do that on physical exam.

06:28 The first is to shine our light into the patient's eyes.

06:32 And as you can see here, we see a reflection.

06:35 And that's that small white ellipse that you see in this patient's two eyes.

06:40 Patients with a skewed deviation with a vertical misalignment, we'll see that reflection hit in different spots, different points of the eye.

06:48 Here you can see in the patient's right eye, the reflection is at a normal level where you would expect it.

06:55 On the patient's left eye, that reflection is lower down in the eye, indicating that there's a vertical misalignment.

07:02 And this is the first tip off on exam that we may be dealing with an abnormal test of skew.

07:09 The second test is to perform an alternate cover test.

07:13 Where we cover one eye and then cover the other asking the patient to fixate on the examiner.

07:19 When one is covered the eye that's uncovered we'll look at the examiner.

07:24 And when we alternate, we see that that vertical misalignment is accentuated and we can see that on exam.

07:32 Again, a normal finding is no skew deviation.

07:36 A normal test of skew, no vertical misalignment.

07:40 And this is reassuring and suggests a peripheral cause.

07:43 An abnormal test is the presence of a skewed deviation.

07:47 A positive test of skew, a finding that indicates that there's a vertical misalignment.

07:52 And this suggests a central cause.

07:54 Of the three exam techniques we talked about, head impulse test, nystagmus, and test of skew, this is the most specific.

08:02 Where if it's positive, this strongly points to a central source.

08:07 Let's look a little bit closer at that alternate cover test.

08:10 Here you can see the two eyes.

08:12 And we're covering the patient's right eye.

08:15 Will alternate back and forth to cover each eye in rapid succession.

08:20 And we're looking for the eyes to bob up and down.

08:23 This alternate cover test accentuates the vertical misalignment in this test of skew.