What are Functional Sensory Symptoms ?

Functional Sensory symptoms describe sensory symptoms anywhere in the body that are due to the nervous system not working properly. They are not caused by damage or disease of the nervous system.
 
Patients with functional sensory symptoms can experience the following:

1. A feeling of altered sensation down one side of the body (more commonly the left) – usually involving the face, arm or leg in various combinations. This is sometimes called ‘hemisensory syndrome’. Facial sensory disturbance alone is quite common.
2. A feeling that a limb just doesn’t belong to them or ‘part of them’.
3. Loss of sensation with sharp edges – sometimes where the arm meets the shoulder or where the leg meets the trunk.
4. Dense loss of sensation – some people with FND find they dont feel anything at all – even painful sensations like someone pressing on a toenail. Thats unusual in other neurological conditions.
5. Fleeting sensations – including twitches, buzzing sensations, electric shock sensations.
6. Sometimes visual symptoms including intermittent blurring and double vision and limb weakness (see ‘Functional Limb Weakness‘ ) may be present on the same side of the sensory symptoms.

To the patient and the doctor, these symptoms can be alarming. They may make you wonder if you have had a stroke or multiple sclerosis.
 
However, functional sensory symptoms are not due to damage to the nervous system which means that they can get better or even go away completely. This is because when people have functional sensory symptoms all the parts of the nervous system are there, they are just not working properly so that your brain does not receive the messages in the normal way.

How is the diagnosis made?

The diagnosis of functional sensory symptoms is usually made by a neurologist.

When the doctor listens to your story and examines you they may recognise your symptoms as typical of functional sensory symptoms. On examination the doctor may find that sensation in the affected area is reduced. There may be a mild degree of weakness in association with the sensory disturbance. The pattern of this weakness and response to specialised tests on examination will help the doctor make a positive diagnosis of your condition.

Normal scans and tests help to make the diagnosis, but the diagnosis is usually made by a neurologist when they first meet you.

How do functional sensory symptoms happen?

Functional sensory symptoms arise for different reasons in different people. The reasons are very similar to those that cause functional weakness. These include

1. After an injury / with pain—People seem particularly vulnerable to functional sensory symptoms after a physical injury or if they have a lot of pain. Studies of patients with chronic pain show that unexpected functional sensory disturbance (usually occurring down one half of the body is quite common). Sometimes functional sensory symptoms occur as part of another condition called Complex Regional Pain Syndrome Type 1 . Click on the link to find out more.
2. With hyperventilation – In addition, functional sensory symptoms are particularly likely to occur along with symptoms of dizziness and intermittent shortness of breath. Studies in volunteers have shown that if you ask 100 people to breathe quickly for a period of time (hyperventilate), then most will get sensory symptoms. This usually consists of tingling in the fingers or around the mouth. This is believed to be due to the effect on nerve endings of a low carbon dioxide that occurs in hyperventilation. In a small proportion of volunteers however, hyperventilation causes numbness down one side of the body.
3. An illness with a lot of fatigue or bed rest— sensory symptoms can develop slowly in people who are suffering from a lot of fatigue or exhaustion. In some patients too much rest can bring the symptoms on. There may be an overlap in this situation with Chronic Fatigue Syndrome. Click on the link to find out more.
4. After an episode of dissociation / panic attack– Functional sensory symptoms like numbness and tingling often occur with other symptoms like lightheadedness and dissociation (a feeling that things around you were distant or disconnected). Dissociation is a bit like a trance and is described elsewhere on this website. Sometimes these episodes are very frightening, especially if they come ‘out of the blue’ and can lead to a panic attack. Once the panic attack is over it can leave behind the feeling that one half of the body is ‘not right’, perhaps heavy or tingly
5. Migraine – Some people with migraine experience sensory symptoms as part of their attack. Sometimes patients with functional sensory symptoms describe an attack that sounds like migraine after which their sensory symptoms remain persistent. In these cases, the migraine has been the trigger for functional sensory symptoms
6. No obvious cause – there may be no obvious precipitant, just as some people with migraine have them only when tired or stressed, whereas some have them for no reason at all