Introduction
If your patient is complaining of impaired sensory function (tingling = paraesthesia, numbness = hypaesthesia or anaesthesia, burning sensation = causalgia, painful skin = hyperpathy) or if, based on the history-taking and / or other findings (atrophy, loss of strength, reflex differences) you suspect that the patient may have a neurological condition, your examination should aim to answer the following questions.
1. Are there objective signs of sensory function impairment?
Procedure
- You should be aware that suggestion can easily lead to both you and your patient falsely assuming the presence of sensory dysfunction.
- First examine the patient with their eyes open, so that they can see which stimuli they are expected to identify.
- Then have the patient close their eyes during the sensory function examination.
- Alter the time interval between the administered stimuli.
- Now and again administer a false stimulus, asking the patient whether they feel the point or the skin contact while you are actually not touching them.
- If in doubt, repeat the examination later on and note whether the findings are consistent.
- Be aware that loss of sensory function is often preceded by reduced sensory function. During the examination you will therefore often find that although the patient can identify all the administered stimuli, they still feel differences, for example between left and right.
2. Where is the lesion located? [Figures 66 and 67]
Figure 66
Figure 67
Procedure
- Mark the area of sensory deficit as accurately as possible so that you can establish whether it involves mononeuropathy, polyneuropathy, a nerve root lesion or a central lesion.
- Examine both the dorsal column sensory function (light touch sensation, vibration sensation and motion sensation) and the spinothalamic sensory function (pain sensation, temperature sensation). The pathway followed by these sensory aspects differs particularly in the spinal cord. All sensory fibres enter the spinal cord via the anterior nerve root. Dorsal column sensory stimuli mostly travel homolaterally via the dorsal tracts (tract of Burdach and tract of Goll) to the central nervous system. The spinothalamic stimuli first cross and then travel along the spinothalamic tract to the central nervous system [Figure 68]. Dorsal column sensory stimuli also cross over, but only at the medulla oblongata. Thus a condition involving the spinal cord can display dissociated sensory deficit, for example intact spinothalamic sensory function, but impaired dorsal column sensory function.
- If you suspect a neurological condition, you should in any case examine the patient’s hands, feet and face, and carry out further examinations based on the symptoms and / or other findings.
- Always compare left and right and different skin regions.
Figure 68
Procedure
Spinothalamic sensory functions
Pain sensation
Snap a cotton bud in two, to obtain a sharp point.
- Let the patient feel the difference between the tip of the cotton bud and the sharp point (blunt-sharp sensation) on an area where you are certain there is no sensory deficit.
- Upon each stimulus ask the patient to indicate whether or not the contact feels sharp.
- If the blunt-sharp sensation is impaired, the terms hypalgesia or analgesia are used.
Temperature sensation
- Instead of having the patient distinguish between sharp and blunt, you can also ask them to assess the difference between hot and cold. To do this, use two test tubes, one of which you have filled with water and stored in the freezer and the other you have filled with warm water.
- Make sure there is an adequate area of contact between the test tube and the patient’s skin.
Dorsal column sensory function
Procedure
Light touch sensation
- Use the tip of the cotton bud.
- Always touch the patient lightly, do not stroke.
- Always ask the patient to say yes when they feel contact.
- Ask the patient to also indicate when the contact feels different, such as dull or tingling.
- Because it can sometimes be problematic to differentiate between loss of function of light and crude touch (= spino-thalamic sensory function), it often better to examine the sense of vibration or motion to determine whether there is loss of dorsal column sensory function.
Vibration sense
- Strike the tuning fork (128 Hz), for example against the ulnar side of the palm of your hand.
- Firmly place the foot of the tuning fork on the first metatarsophalangeal (MTP1) joint.
- Ask the patient whether they feel the vibrations [Figure 69].
- To be sure that the patient is feeling the vibrations and not just the tuning fork touching their skin, ask them to close their eyes and indicate when the vibration stops.
- Stop the vibration in the tuning fork without altering the pressure on the MTP1 joint [Figure 70].
- If the sense of vibration on the MTP1 is impaired, investigate the vibration sense on more proximal bony extremities (malleolus, tibia, metacarpal joints, wrist).
Figure 69
Figure 70
Sense of movement and sense of direction
- Hold the patient’s big toe between your thumb and index finger.
- Make sure that neither the patient’s toe nor your fingers touch the other toes [Figure 71].
- Ask the patient to keep saying yes when you move their toe.
- Start with large movements; if even these are not felt, test the sense of movement in the ankle and the knee as well.
- If the patient feels the movement, enquire about the direction of the movement.
- The procedure for determining the sense of movement in the upper extremities is the same as above.
Figure 71
Interpretation
- In people older than 60 years of age, there is often a loss of vibration sense, without this being indicative of any pathology.
- The sense of vibration and sense of movement are often impaired before the sense of light touch.
- On the basis of the distribution and nature of the sensory deficit, it is often possible to locate the lesion [Figures 72-75].
Figures 72 – 75