Limbs: reflexes and sensation

Published on 10/04/2015 by admin

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Limbs

reflexes and sensation

Examining reflexes

Tendon reflexes are single synapse reflexes. A rapid stretch of the muscle stimulates the muscle spindles and this message is conveyed via the sensory root to the spinal cord at the segmental level of the muscle stimulated. This synapses with the motor neurone that supplies the muscle and leads to contraction of the muscle.

If this is interrupted, by either peripheral sensory or lower motor neurone lesions, the reflex is reduced or lost. Reflexes are reduced in muscle disease. If there is an upper motor neurone lesion, the reflex is increased because inhibitory factors have been removed.

Tendon reflexes are important because they provide an objective sign indicating abnormality and some indication as to the level of the abnormality.

Reflexes can be graded as absent, obtainable with reinforcement (see below), reduced, normal, increased and increased with clonus.

How to elicit tendon reflexes

The patient needs to be relaxed, with the muscle to be tested in the middle of its range of movement (Figs 1–3). The tendon hammer is swung to hit the tendon or, for the biceps and supinator reflexes, a finger on the tendon. The muscle is watched for movement in response to this. If the reflex is not obtainable then the patient is asked either to clench the teeth or make a fist – reinforcement – which may allow the reflex to be found. When testing the reflexes it is useful to remind yourself of the segmental level being tested.

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Fig. 1 Testing reflexes in the arm.

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Fig. 2 Testing the knee reflex: L3/4.

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Fig. 3 Testing the ankle reflex: S1.

Clonus is the rhythmic contraction of a muscle when it is stretched. This is most commonly found at the ankle (up to three beats is normal) and is occasionally found at the knee. Clonus indicates an upper motor neurone lesion.

Plantar response or Babinski response

This neurological sign has attained almost mythical status. An extensor plantar response is when the hallux extends and the other toes spread out in response to a stimulus. This stimulus is usually stroking the lateral part of the sole, though there are numerous alternatives, with different eponyms. This extensor response indicates an upper motor neurone lesion. Difficulties arise from false-positive results, especially when the patient withdraws or when there is a ‘dystonic toe’ in extrapyramidal disease, and from too great an emphasis being put on the sign. False-negative responses arise when there is sensory loss on the sole or profound weakness of toe extension. An extensor plantar response needs to be interpreted within the context of the rest of the motor examination.

Abdominal reflexes

These reflexes are not stretch reflexes. The muscles of the abdominal wall contract in response to a scratch of the skin of the same segmental innervation. The abdomen is usually considered in four quadrants. A response is normal. In upper motor neurone lesions, after multiple abdominal operations or multiple pregnancies, the response is lost. It is invisible in obesity.

Sensory examination

This section will describe some background and the techniques of sensory testing. The findings and their interpretation are discussed on pages 60–61.

There are five commonly tested modalities of sensation. These are subserved by particular-sized axons and run in particular tracts.

Joint position sense (proprioception) and vibration sense are carried in large myelinated fibres and then run in the posterior columns of the spinal cord. These remain on the same side until the medulla, where they cross over.

Pain, which is tested by using pinprick, and temperature are conveyed in small fibres, including unmyelinated fibres, and they run in the spinothalamic tracts. These cross over and synapse within one or two levels of entry into the spinal cord.

Light touch is conveyed to a degree in both systems. Loss of joint position sense and vibration sense is frequently dissociated from loss of pain and temperature; light touch is not usually helpful in this situation.

How to examine sensation

Sensory examination requires the patient’s cooperation, understanding and often patience. The degree of detail depends on whether there are sensory symptoms or other signs that make sensory examination important. It is easiest to start with the modalities that are easiest to test.

Remember that you need to teach the patient about the test, then undertake the test and have a system to check the validity if you are in doubt.

Vibration sense

Use a 128 Hz tuning fork.

image Teach: Set off the tuning fork and apply this to the sternum to allow the patient to experience the feeling of vibration.
image Test: Ask the patient whether the vibration is felt when it is applied to the bony prominences (Fig. 4). If this is perceived distally, there is no need to proceed proximally.
image Check: Apply the tuning fork, having stopped it vibrating, and ask the patient if vibration is still felt.
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Fig. 4 Sites for testing vibration sense and key dermatomes to remember.

Joint position sense

When testing joint position sense, hold the joint so that your grip is perpendicular to the direction of joint movement (Fig. 5). Normally, small movements are perceived. Testing patients without neurological problems allows you to establish a ‘normal range’.

image Teach: Move the joint with the patient’s eyes open, indicating which way is up and down.
image Test: With the patient’s eyes closed, move the joint up and down, asking the patient to tell you the direction of movement. Start with large movements and gradually reduce them until the patient makes errors.
image Check: Repeat the test for the lowest amplitude movements perceived. (See also Romberg test, p. 28.)
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Fig. 5 Testing joint position sense.

Pinprick

Use a slightly blunted pin, preferably a pin developed for this purpose. Do not use hypodermic syringe needles, which puncture the skin and leave a dotted line of marks.

image Teach: Touch an area of clinically unaffected skin with a pin and inform the patient that ‘this is a pin’.
image Test: Start distally or in a clinically affected area. Work proximally. Ask the patient to close the eyes and tell you when the pin feels sharp; if abnormal, map out the affected area.
image Check: Occasionally use a blunt stimulus, such as the opposite end of the designed testing pins, which the patient should recognize as blunt.

Temperature

This can be tested at the bed side using a tuning fork, which feels cold. More formal testing requires matched dry test tubes filled with warm and cool fluids.

image Teach: Touch the patient on an unaffected area with the side of the tuning fork so that the patient knows how cold the fork is.
image Test: Touch the affected area and map out any area of altered sensation.
image Check: This can only be done using hot and cold test tubes by varying the order of application of the tubes.

Light touch

This can be tested using cotton wool or a fingertip.

image Teach: Show the patient what the stimulus feels like on an unaffected area.
image Test: Start distally or in a symptomatically affected area. Ask the patient to tell you when the sensation is felt and whether the sensation feels normal.
image Check: Vary the frequency of testing.

Special situations

Inattention, agraphaesthesiae or astereoagnosia are all signs of contralateral parietal lesions. Before testing, check that there is normal superficial and posterior column sensation.

Inattention

Ask the patient to close the eyes and tell you which side you are touching: touch one side, then the other, and then both. Patients with inattention will correctly recognize the side on single stimulation, but only one side on bilateral stimulation.

Agraphaesthesiae

Write a letter or number with your finger on the palm of the patient’s hand. Normally this is readily recognized. If not, there is agraphaesthesiae.

Astereoagnosia

Ask the patient to identify an object, such as a coin or key, put in the hand.

Limbs reflexes and sensation

image Tendon reflex changes are ‘hard’ neurological signs.
image The plantar response is very helpful but needs to be treated with caution when the result is ‘surprising’.
image Sensory examination needs concentration and patience from both patient and examiner. This may need repeating.

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