When examining an abnormal area, ask the patient to close their eyes and say ‘yes’ every time contact is made. When looking for changes in sensation, ask whether each stimulus is normal or abnormal. Move from insensitive to normal areas or from normal to hyperesthetic, varying the rate and the rhythm of the stimuli. Gently mark the boundaries of change with a biro or skin pencil. This enables you to check consistency of response and also to reproduce these markings in diagrammatic form.
Start with the wrist and ankle on each side; progress proximally to the olecranon and acrominion, and to the patella and anterior superior iliac spine, if there is a distal sensory abnormality.
Touch and light pressure are transmitted in the dorsal column to the postcentral cortex. Initially test them by finger contact over the affected area, and then detailed mapping with a wisp of cotton wool or an artist’s paintbrush (figure 19a,b). Initially let the patient watch while you apply the stimulus, to ensure a positive response is appreciated: compare it with the contralateral side.
Two blunt points are distinguished as separate contacts at varying distances in different parts of the body (figure 19c): lips and tongue 2–3 mm; fingertips 3-5 mm; dorsum of the fingers 4–6 mm; palms 8–15 mm; dorsum of the hands 20–30 mm; dorsum of the feet 30–40 mm; and the back 40–50 mm.
Pain and temperature are carried to the level of sensory awareness in the spinothalamic tract. Test the former with a sterile pin or a partially blunted needle (figure 19d). Ask the patient to respond to each contact, stating whether it feels dull or sharp.
Gross temperature difference is detected by comparing the warmth of the side of your finger with the cold of the side of a tuning fork (figure 19e,f). More precise mapping is with test tubes of warm and cold water. Temperature changes may be more consistent than those with a pinprick. Mapping follows the same routine to that described for touch.
Vibration sensation is assessed by applying the base of a clinical tuning fork to a bony prominence (figure g–j). The stimulus is generated by lightly tapping the fork on your hypothenar eminence. Strike the tuning fork before each application and ask the patient with their eyes closed, whether vibration is present and when it stops. Occasionally deliberately stop the vibration of the tuning fork to assess the accuracy of response. The feet are particularly important to assess for distal neuropathy in a diabetic patient.
Graphesthesia is assessed by writing numbers or letters on each palm, forearm or the anterior compartment of each shin (figure 20). Use a blunt object, such as the blunt end of a pen or pencil. With the patient’s eyes closed, give examples for orientation and then assess; the numbers 3 and 8 are useful stimuli.
Assessment of size, shape and weight (stereognosis) is with common objects placed in the palm of the hand, with the patient’s eyes closed. Useful. stimuli are, pens, pencils and keys (figure 21).
Sensory inattention is typical of parietal lobe lesions. It is elicited by the simultaneous application of stimuli on the two halves of the body (figure 22). The patient has their eyes closed and occasionally only one side is touched.
Examine joint position sense in the upper and lower limbs, starting distally and moving proximally if a defect is elicited. Hold the hand or foot with your left hand and with the right index finger and thumb gently grasp each side of the terminal phalanx of the index finger or great toe. Indicate to the patient up and down movements and then, with their eyes closed, ask them to identify a series of movements, inserting ups and downs in a random fashion. The normal subject can perceive minimal change of angulation (figure 23a–d).
Check for deep pain sensation by squeezing the tendo Achilles from side to side or pressing the base of the thumb or great toenail.
A useful initial test of neurological function of the upper limbs including position sense, power and coordination is to ask the patient to extend both arms with the palms outwards, and upwards or downwards with their eyes closed and observe any unconscious drift (figure 24a,b).
The Romberg sign (see above) is associated with asking the patient to stand upright with their feet together and eyes closed. Make sure you guard against any fall. An initial gentle sway of the body is normal but in abnormalities of dorsal column function, the patient is unable to stand unaided.
Lumbar puncture provides access to the epidural and subarachnoid spaces: both of these sites are used in various anesthetic techniques. In examination of the nervous system, the technique is used primarily to sample cerebrospinal fluid, it must never be undertaken in cases of known or suspected raised intracranial pressure and, as with all invasive procedures described, full aseptic precautions must be in place.
The entry site is above or below the fourth lumbar spine (sited in the supracristal plane (figure 25a). The procedure may be undertaken in the sitting or lying position (figure 25b,c). In the former, have the patient leaning forward over the back of a chair, or over the side of a bed. In the latter, their head and knees should be tucked into the body, with their back near, and parallel to, the edge of the bed.