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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’. Functional weakness may also be described as 'dissociative motor disorder' and less helpfully as "conversion disorder."
To the patient and the doctor it often looks as if there has been 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.
The diagnosis should usually be made by a consultant neurologist so that other neurological causes can be excluded. The diagnosis should be made on the basis of positive features in the history and the examination (such as Hoover's sign). It is dangerous to make the diagnosis simply because tests are normal. Neurologists usually diagnose wrongly about 5% of the time (which is the same for many other conditions.)
Many patients with functional weakness suffer from not being believed. Although psychological factors can be important they are not exclusively so and the problem is not 'made up' or 'imagined'. Patients with functional weakness are as disabled and distressed by their symptoms as patients with multiple sclerosis.
Treatment involves understanding and believing the diagnosis and gradually restoring nervous system function with graded exercise, learning how to manage symptoms of fatigue and pain when present and treatment of associated symptoms of worry or low mood if present. Hypnosis may also be useful.
Giveway weakness (also "give-away weakness", "collapsing weakness", etc.) refers to a symptom where a patient's arm, leg, can initially provide resistance against an examiner's touch, but then suddenly "gives way" and provides no further muscular resistance.