What is Functional Weakness ?
Functional weakness is weakness of an arm or leg due to the nervous system not working properly. It is not caused by damage or disease of the nervous system.
Patients with functional weakness experience symptoms of limb weakness which can be disabling and frightening such as problems walking or a ‘heaviness’ down one side, dropping things or a feeling that a limb just doesn’t feel normal or ‘part of them’.
To the patient and the doctor it often looks as if you have had a stroke or have symptoms of multiple sclerosis. However, unlike these conditions, with functional weakness there is no permanent damage to the nervous system which means that it can get better or even go away completely.
How is a diagnosis of functional weakness made?
The diagnosis of functional weakness is usually made by a neurologist or stroke physician.
Patients with functional weakness have normal scans and other tests. When they are examined, the doctor usually finds a pattern of weakness typical of this problems and does not find changes in reflexes or other evidence of a structural neurological disease (like stroke).
This is because in functional weakness all the parts of the nervous system are there, they are just not working properly so that when you try to move your arm or leg it doesn’t do it as well as it should.
Your doctor may be able to find specific physical signs of functional weakness when you are examined and make the diagnosis in the same way as you would with a condition like migraine (which also does not have a ‘test’)
Signs of functional weakness include t:
• Collapsing weakness – this is a tendency for an arm or leg to ‘collapse’ when being tested. This may be interpreted by a doctor as ‘not trying’. In fact, patients with functional weakness typically find that the limb gets weaker the more they try
• Hoover’s sign – in this test, your affected leg may be weak when you try to push your foot down into the bed. However, when the doctor asks you to push up with your other leg the strength in your affected leg returns. Some patients with functional weakness use this sign as a form of physiotherapy to encourage normal movement in their affected leg (and to help demonstrate to themselves that the diagnosis is correct)
• A dragging kind of walk – Patients with functional leg weakness sometimes have a very characteristic way of walking which means that their affected leg “drags” along the ground. This is different to someone with a stroke or multiple sclerosis who swings their leg if they are able to stand up.
• A difference between the examination of power on the bed and when walking – some people with functional weakness have relatively normal examination of strength in the legs on the bed but weak legs when walking. The reverse can also be true. This is not because they are not trying to walk, the variability is a key feature of the diagnosis.