Numbness and sensory disturbance

What is it?

Sensory symptoms can be broadly divided into:

positive symptoms: an intrusive feeling of altered sensation, often referred to as numbness, tingling, pins and needles, though sensations may include pain

negative symptoms: the realization that sensation is lost, usually noticed when the patient inadvertently touches the affected part.

Patients will often describe sensory disturbance as ‘numbness’ and this term alone can be used to mean:

loss of sensation – a negative symptom

a positive feeling of altered sensation – ‘like the sensation as a local anaesthetic wears off’

pain

A limb may be described as numb when it is in fact weak, or vice versa.

Tingling or pins and needles can usually be readily recognized as a distinct sensory symptom. Usually this can be localized more accurately than other positive symptoms.

Loss of joint position sense (proprioception) is more likely to be described as clumsiness or unsteadiness or like having a tight bandage on rather than numbness. Cortical sensory loss is usually noticed because of the disturbance in function, with clumsiness or incoordination more prominent than sensory symptoms.

Negative sensory symptoms, or the finding of sensory loss without associated symptoms discovered on examination, occur particularly in the following situations:

If the sensory loss is very longstanding or of slow onset, for example hereditary neuropathies.

When a cortical lesion also causes inattention so the area is ignored.

If in an area that is not functionally important, for example the thoracic dermatomes.

Where is it?

The distribution of the sensory symptoms and signs is important in determining the cause of the symptoms (Fig. 1). The common patterns of sensory symptoms follow the patterns of sensory loss illustrated. However this can be imprecise. For example, patients with carpal tunnel syndrome commonly feel their whole hand is numb, sometimes even the arm. Their feelings of tingling are usually more clearly localized to the hand, though they may be uncertain which fingers are affected. Patients with cervical root compression often describe numbness affecting the whole arm; their tingling however normally is more clearly related to a single root dermatome. In other circumstances, even relatively minor symptoms can be very helpful. For example, a patient with numbness and weakness in both legs with upper motor neurone signs could have a problem at any level of the spinal cord, or possibly brain stem. If they have sensory symptoms or signs in the arms, this indicates the level to be in the cervical cord or above.

Fig. 1 Sensory loss and associated conditions.

How did it come on?

Important clinical features are the timing of the onset and pattern of sensory disturbance.

Transient sensory disturbance

Transient disturbances of sensation can arise from any level in the nervous system:

Cerebral hemisphere and brain: include migraine, epilepsy, transient ischaemic attacks, and CNS demyelination.

Nerve roots and peripheral nerves: compressive radiculopathy and peripheral nerve compression.

These types of symptoms are also often unexplained or may be psychogenic.

The timing of the onset and its duration, as well as the distribution, helps clarify this (Table 1).

Table 1 Causes of numbness and of sensory disturbance

Persistent sensory disturbance

The distribution of sensory disturbance and any associated motor or other signs are helpful in localizing the lesion. The timing and evolution give additional information regarding aetiology in this group as well. In addition, sensory deficits can be progressive, reflecting progressive disease. The nature of this will depend on the affected level of the nervous system; some examples include:

brain – infarction, haemorrhage, demyelination or space-occupying lesions (such as tumours)

spinal cord – demyelination, cervical spondylitic myelopathy

nerve root – spondylitic radiculopathy

peripheral nerve – peripheral neuropathy, common cause diabetes mellitus (pp. 102–105).

When there are persisting sensory symptoms, more information can be obtained from examination. When examining for sensory loss, ignore equivocal findings, concentrate on definite abnormalities and map out their boundaries. The area may need to be re-examined to confirm the findings. This may allow a more definite pattern of sensory loss.

Sometimes sensory examination can be normal or minimally abnormal despite quite marked persisting symptoms. This can either reflect a central lesion or a non-organic sensory disturbance.

Understanding sensory loss will depend on the integration of sensory and motor signs.

Numbness and sensory disturbance

Sensory examination is an imprecise art. The subjective description of the cutaneous sensory abnormality is of limited value in diagnosis.

The timing of the onset of paroxysmal sensory symptoms is important in diagnosis.

The distribution of sensory loss is important in localizing the causative lesion.

Sensory symptoms and signs need to be integrated with other findings when trying to make a diagnosis.