Year 2 MBChB

Clinical Skills Session

Examination of the Sensory System

Reviewed & ratified by:

Dr D Smith Consultant Neurologist

Dr R Davies Consultant Neurologist

Dr B Michael Neurology Clinical Lecturer

Dr J Williamson Neurology Registrar

Dr A Clarke GP

Aug 2018

Sensory Examination

Learning objectives

o To know the basic anatomy and function of the sensory system

o To be able to understand and carry out a bed side assessment of the sensory system and assess co-

ordination

o To adhere to waste disposal policies including sharps and clinical waste

The sensory system

Sensory information is detected at the peripheral receptors, travels via peripheral nerves, nerve roots, spinal cord,

brainstem and thalamus to sensory cortex. There are 2 pathways, spinothalamic tract and posterior (or dorsal)

column.

o Pain, light touch and Temperature sensation are carried by small unmyelinated fibres in the

spinothalamic tract. This decussates (crosses over) immediately in the spinal cord

o Vibration and Proprioception (joint position) are carried by large myelinated fibres in the Posterior (or

dorsal) columns. They ascend on the same side of spinal cord and cross over in the brain stem.

Indications for sensory examination

The following list of potential indications is by no means exhaustive, a patient may present with;

o Paralysis or changes in sensation

o Unexplained muscle weakness

o Stroke

o Trauma – spinal cord injury or direct brain injury

o Autoimmune disease / metabolic disease (Lysosomal storage disease, rare)

o Congenital conditions

o Diabetes

Spinal cord section

Normal sensory examination

Normal sensation allows a patient to detect;

o pain (pinprick), light touch and temperature in whichever area is tested,

o vibration at tips of fingers and toes and

o proprioception (joint position) (i.e. small amplitude movements) at distal joints

A sensory examination is not routinely performed but is only done with certain clinical presentations i.e.

when the patient complains of altered sensation or when the patient has impaired balance

Sensory pathway

Localisation of problems can be determined by knowledge of the area of skin supplied by peripheral nerves, sensory dermatomes, decussation of spinothalamic tract and dorsal columns.

Dermatones

A dermatome is an area of skin supplied by a single spinal nerve for the modalities of sensation. Knowledge of the dermatomes can help to localise problems involving the spinal cord or nerves. Please note the dermatome borders will differ from one text book to another as indeed they do from one individual to another. It is not an exact sceience.

Dermatomes of the upper limb

Dermatomes of the lower limb

C3

C4

C5

C6

C8

T1

T2 C5

C6

S4

S5 L1

L2

L3

L4

L5

S1

S2

S

C7

Dermatomes of the trunk

Another example of dermatomal distribution

C2 C3 C4

T2

T5

T10

V1

V2

V3

Patient Safety

In clinical practice

Encourage the patient to describe the distribution of altered sensation. Initially demonstrate the test chosen to

assess sensation in an area of skin the patient perceives to be normal and test that sensation within the area

reported to be abnormal. Map the extent of altered sensation by asking the patient to confirm that the sensation

demonstrated i.e. light touch, feels the same on the area of concern. Then decide if this area relates to/ or is

associated with a spinal, dermatomal or peripheral /cutaneous nerve pattern of altered sensation.

Testing light touch

o Use fingertip / cotton wool or a

monofilament (usually found in diabetic

clinics)

o Ask the patient to respond when stimulus is

detected and confirm that it feels the same

as the test site.

o Dab the skin and then withdraw the stimulus

- do not drag, stroke or tickle as this

stimulates the hairs on the skin

o Compare one side with the other

Testing vibration sense

With a 128 Hz tuning fork create vibration by either taping it gently against your hand or by pushing the prongs

towards one another. Wait for the audible sound to disappear before placing on the patient. Demonstrate on a

bony prominence away from the affected area (forehead or sternum for example). To avoid reducing the vibration

hold at the round thumb rest just under the fork, the flat rest at the base is held against the patient.

Place the base of 128 Hz tuning fork on the most distal point of the limb

being tested i.e. tip of a finger or toe. Any finger or toe may be tested as it

makes no difference. (In choosing a toe, it is easier to use a larger toe for the

practicality of testing) Ask the patient ‘Can you feel that?”. If they cannot,

move proximally, testing vibration sense at bony prominences (radial styloid

process, olecranon etc) until the vibration is detected. If the patient’s

vibration sense is abnormal record as ‘absent below….’

Pain - sharp

o Use a disposable neurotip, or an unfolded paper clip

o Do NOT use a hypodermic needle

o Explain and demonstrate the stimulus with the

“sharp” on an unaffected area

o Then go directly to the area, which the person

perceives to be abnormal and map out the

distribution of the abnormality.

o This should then be recorded as ‘impaired cutaneous

perception to pinprick in e.g. a stocking distribution

bilaterally.

o Always dispose of “sharp” safely

Testing proprioception

Hold the patient’s fingertip between your fore finger and thumb,

ensuring you hold the sides of the finger. Avoid holding from

above and below as the patient may sense up and downwards

pressure, therefore giving false results.

Demonstrate what you are going to do by moving their fingertip

up and down whilst they watch.

To test proprioception, ask the patient to close their eyes. Repeat

the movements moving the fingertip randomly up or down in

small incremental movements and ask the patient to confirm what

direction their finger has been moved in.

If the patient cannot detect small amplitude movements,

or makes errors, increase the amplitude of movement. If

the patient cannot detect larger amplitude movements,

test proprioception at a more proximal joint. If the joint

position sense is abnormal it is recorded for example as

“absent below” ankle bilaterally or, if milder, ‘errors of’ at

the great toes bilaterally.

Proprioception – order of testing

Remember proprioceptive sense tends to decline with age;

Upper limb o Distal interphalangeal joint o Proximal interphalangeal joint, o Metocarpophalangeal joint o Wrist o Elbow o shoulder

Lower limb o Interphalangeal joint of the hallux, o Metatarsophalangeal joint, o Ankle o Knee

Hip

Testing proprioception of the finger

Romberg’s test

The patient should stand with their feet 6 inches apart, arms by their sides and eyes closed, the patient

should then count to 10. The examiner should stand behind or beside the patient with arms around but

not touching them.

If proprioception is intact balance is maintained. This is a negative Romberg's test.

If proprioception is known to be lost, do not perform this test

Patterns of sensory loss

As with motor examination, the pattern of sensory loss helps to localise a lesion to specific parts of the nervous

system. The initial distinction is whether the lesion is in the central or peripheral nervous system.

A good way of achieving this is to recognise patterns of sensory loss caused by

o spinal cord lesions (central)

o peripheral neuropathy (peripheral)

Spinal cord lesion

With a spinal cord lesion sensation is lost or altered below the level of the lesion, this is called a sensory level. The

extent of the lesion determines whether the loss of sensation is uni- or bi-lateral

Familiarise with the cross-sections of the cord and sites of where the main tracts decussate (cross over), this will

enable you to understand the detail of the pattern of sensory loss.

Peripheral neuropathy

Loss, or altered, sensation starts at the end of the longest nerves; i.e. in the toes and spreads proximally

The fingers are affected after the toes/feet

This produces a “glove and stocking” pattern of sensory loss

The type of nerve fibre affected (myelinated, unmyelinated or both) determines which modalities are lost.

Further Reading

https://geekymedics.com/dermatomes-and-myotomes/