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Neurophysiology (NCS, EMG and EEG)

Neurophysiology (NCS, EMG and EEG)

Nerve conduction studies and EMG can be a powerful diagnostic tool. However, they are uncomfortable for the patient and a scarce resource, so this guidance is designed to ensure appropriate and optimal use. This list is not exhaustive and the emphasis is on common indications.

Those indications where a neurological assessment prior to neurophysiology is advised are marked *
Those where neurological assessment prior to neurophysiology is strongly advised are marked **

1. Nerve Conduction Studies and EMG

Clear indications


Carpal tunnel syndrome - if conservative measures have failed and surgery is considered
Ulnar neuropathy - if conservative measures have failed and surgery is considered
Clinically significant neuropathy** - (without clear cause) especially if acute onset, disabling or multifocal
Suspected Motor neurone disease**
 

Probable indications

– where tests may support diagnosis or provide prognosis


Radial and Common peroneal palsy* without clear cause.
Brachial plexopathies** of unknown cause.
Myaesthenia gravis**
Chronic neuropathy** where history, examination and blood tests do not identify cause.
Generalised weakness** of uncertain cause.
Focal weakness** of uncertain cause.
Foot drop** of uncertain cause.

Possible indications - where other tests are better or result has little impact on management


Carpal tunnel syndrome - when surgery is not being considered
Ulnar neuropathy - when surgery is not being considered
Chronic non-disabling symmetrical sensorimotor neuropathy* - aetiological diagnosis may be forthcoming from history or blood tests.
Myopathy** - alternative tests: genetic studies or muscle biopsy
Sensory* symptoms of uncertain cause.
 

Indications with low or limited yield


Suspected radiculopathies
Suspected lesion of lateral cutaneous nerve of the thigh
Focal pain of uncertain cause.

 

2. EEG


EEG is not "the test for epilepsy" because it has significant false positives and negatives.  A normal EEG does not exclude epilepsy and an abnormal EEG without a typical clinical seizure sdoes not make a diagnosis of epilepsy; results must be interpreted within the clinical context.

EEG can be used:

 

To assess risk of recurrence following a single seizure*

To classify clinically confirmed seizure*

To assess patients with possible encephalopathy and non-convulsive status epilepticus*

As an aid to diagnosis in some patients with dementia*