In the Overview of Clinical Neurophysiology the techniques are briefly described. In the Clinical Indications, specific conditions, appropriate neurophysiological investigations and their relative worth are listed, based on current best practice, evidence base and opinion of the local Consultants.

1. Indicated. When an investigation is most likely to contribute to clinical diagnosis and management.
   
   
2. Not indicated initially. This includes situations where experience shows that the clinical problem usually resolves with time or early investigation may produce ‘reassurringly’ false negative results. We therefore suggest deferring the study and only performing it if symptoms continue (‘watchful waiting’). Neuropraxia after nerve compression (“saturday night palsy” or carpal tunnel syndrome during pregnancy are typical examples).
   
   
3. Not indicated. Examinations in this group are those where the supposed rationale for the investigation is untenable as the investigation is often normal or not specific, and therefore neither rules in nor rules out the disorder. Experience shows that these conditions often have no demonstrable neurophysiological basis. (e.g. EEG for the investigation of aggressive outbursts, headaches or migraine).
   
   

Overview of Clinical Neurophysiology

Clinical Neurophysiologists undertake a variety of recordings and measurements of the electrical activity of the central and peripheral nervous systems. This information can be used to aid the diagnosis and management of a wide range of neurological conditions in all age groups. Activity is usually divided into four areas:

Electroencephalopathy (EEG)

The electrical activity of the brain (the EEG) can be recorded using either scalp (surface) or, in special circumstances, intracranial electrodes. The majority of studies are undertaken on an outpatient basis using scalp electrodes. Recordings may last from 20 minutes to several hours, particularly if a period of sleep is included. The principal indication for EEG is in the investigation of epilepsy and other disorders of consciousness.

Since it is rare for brief recordings to capture a clinical attack, these EEGs are usually referred to as interictal recordings. Interictal EEG is used to support a clinical diagnosis of epilepsy and to help classify the type of seizures and epilepsy syndrome, and include photic stimulation and hyperventilation with informed consent. A “normal” interictal EEG does not exclude a diagnosis of epilepsy.

EEG is also used in the diagnosis of other conditions such as encephalitis, Creutzfeldt-Jacob disease, coma, and dementia due to neurodegenerative disease.

1. Clinical Indications For Electroencephalography (EEG)
   
   
1. Seizures: to support the diagnosis of epilepsy, help determine seizure type and epilepsy syndrome (NICE Clinical Guideline 20, October 2004).
2. To assess the risk of seizure recurrence after a first unprovoked seizure.
3. Any undiagnosed coma, stupor or unconsciousness (because of the possibility of Non-Convulsive Status Epilepticus).
   
   
2. Clinical Conditions where EEG is Not Indicated Initially
   
   
1. General screening of Psychiatric patients.
2. Intellectual impairment or “early” dementia >60 years of age.
3. Probable syncope (risk of false positive result)
   
   
3. Clinical Conditions where EEG is Not Indicated
   
   
1. Headaches and migraine.
2. To “exclude” a diagnosis of brain tumour.
3. Dizziness and fatigue.
4. Attention deficit disorder.
5. Aggression.
   
   

Nerve conduction studies (NCS) and electromyography (EMG)

NCS recordings are made using electrical stimulation of the peripheral nerves. EMG activity measures the spontaneous and voluntary electrical activity produced in skeletal muscle. Many general medical disorders, as well as neurological disorders and trauma, can cause damage to the peripheral nervous system. NCS and EMG can identify and characterise the site and nature of the pathological processes affecting the peripheral nervous system.

1. Clinical Indications For Nerve Conduction Studies (NCS/EMG)
   
   
1. Polyneuropathy of unknown cause (allowing classification into axonal or demyelinating types).
2. Mononeuropathy that cannot be localised clinically or requiring localisation pre-operatively when there is co-existant pathology (e.g. Carpal Tunnel Syndrome and cervical spondylosis +/- radiculopathy).
3. Mononeuritis multiplex.
4. Disorders of neuromuscular junction i.e. myaesthenia gravis, LEMS.
5. Disorders of anterior horn cells i.e. motor neurone disease.
   
   
2. Clinical Conditions where NCS/EMGs are Not Indicated Initially
   
   
1. Polyneuropathy of known cause complicating metabolic/systemic conditions (e.g. diabetes mellitus/impaired GTT, alcohol abuse, uraemia, vitamin deficiency, GI disorders or neurotoxic drugs).
2. Suspected large fibre polneuropathy but no clinical signs (in particular those with brisk reflexes).
3. Clinically isolated small fibre neuropathy (as standard NCS are normal).
4. Children with pes cavus, normal neurology and no family history of hereditary neuropathy.
5. Radiculopathy if the diagnosis is secure on clinical and imaging findings (e.g foot drop due to L4/5 radiculopathy).
6. Clinical and family history suggestive of genetic or metabolic myopathy – biopsy and/or genetic tests provide more definite diagnosis.
7. Post-polio syndrome.
8. Chronic fatigue syndrome.
   
   
3. Clinical Conditions where NCS/EMGs are Not Indicated
   
   
1. Pain syndrome without ‘neurology’ (no signs) and negative imaging.
2. Certain “controversial” entrapment mononeuropathies including meralgia paraesthetica, radial tunnel sydrome, tarsal tunnel syndrome.
3. Myalgia – no weakness or objective signs and only mildly elevated CPK (<2 times upper limit of normal).
4. Endocrine, metabolic and steroid myopathy.
5. Fibromyalgia and Polymyalgia rheumatica.
6. Vascular thoracic outlet syndrome.
   
   

Evoked potential (EP) studies

These studies are used to monitor the response of the peripheral or, more commonly, central nervous system to a variety of sensory or cognitive stimuli. In our practice these are most often used as paraclinical tests to support the diagnosis of multiple sclerosis, help predict neurological outcome in comatose patients and classify myoclonus.

Intraoperative monitoring (IOM)

Monitoring Evoked Potentials, and in some cases EEG and NCS/EMG, can protect various neurological structures and systems during neurosurgery or orthopaedic surgery. Examples include spinal surgery, posterior fossa surgery for acoustic neuroma and trigeminal neuralgia. Monitoring during functional neurosurgery for disorders such as Parkinson’s disease and pain relief surgery can identify the correct neural structures for stimulation and lesioning.