Clinical neurophysiology is a branch of medicine concerned with measurement of the activity of the central and peripheral nervous systems, various sensory systems, the autonomic nervous system and skeletal muscles.
During surgery, clinical neurophysiological methods are used to monitor important structures and functions. This is done to ensure the best possible results of surgery and to preserve the patient's functional capacity as well as possible.
Serial navigated transcranial magnetic stimulation can be used to treat depression, tinnitus and pain, for example.
Clinical neurophysiological investigations are often sensitive but, as far as the aetiology of the lesion is concerned, non-specific.
Some of the investigations are uncomfortable for the patient. Neurophysiological investigations are therefore not suitable for screening purposes.
There are no contraindications or age limits.
To assess the significance of any findings, the question needs to be clearly formulated.
Electroencephalography (EEG)
Indications
Diagnosis and differential diagnosis of episodic symptoms, epilepsy and epileptic seizures
Diagnosis and differential diagnosis of status epilepticus, particularly nonconvulsive status epilepticus, in an unconscious patient
Antiepileptic medication need not be discontinued for the EEG recording.
In a patient with suspected epilepsy, there is a strong correlation between an epileptiform EEG pattern and the diagnosis of epilepsy and its type (primary generalised epilepsy, focal epilepsy) especially in adults. The correlation of other abnormalities with epilepsy is uncertain.
Epileptiform phenomena are known to occur more readily if the patient is tired or during light sleep; if so, a sleep-deprived EEG should be done after the patient has stayed up for part or the whole of the night. In children and neonates one will usually try to record a sleep EEG.
Special EEGs (to be arranged with the department of clinical neurophysiology): ambulatory EEG, videotelemetry EEG, quantitative EEG analysis, investigations in preparation for epilepsy surgery
Continuous EEG monitoring with a few channels may be used, for example, during status epilepticus in order to assess treatment response. In the treatment of prolonged status epilepticus, EEG monitoring should always be available.
EEG is also used in neonatal monitoring, as well as in assessing hypoxic-ischaemic damage and the depth of anaesthesia.
Electroneuromyography (ENMG)
ENMG provides information about the functioning of the thickest motor and sensory peripheral neurofibrils and skeletal muscles. The functioning of thinner fibrils mediating pain, cold and heat sensations cannot be examined with regular ENMG. The functioning of the myoneural junction can be studied using repetitive nerve stimulation or single fibre EMG.
Separate studies are performed on the conduction of nerve impulses (electroneurography) and on muscle function using a needle electrode (electromyography).
Most common indications
Nerve entrapment, local damage to the nerve: entrapment of the median nerve in the region of the carpal tunnel, ulnar neuropathyin the region of the elbow, radial neuropathy in the upper arm, peroneal neuropathy in the region of the knee
Clinical examination of a nerve entrapment, such as carpal tunnel syndrome, may reveal nothing abnormal, although the patient gives a history of repeated episodes of numbness, particularly at night and in association with using the hand to grip or hold objects, the symptoms being alleviated by shaking the hand.
Suspected axon damage is the most common reason for referral. Needle EMG findings indicative of axon damage (fibrillation, denervation) take about 3 weeks to appear. If ENMG investigations are required earlier than this, a clinical neurophysiologist should be consulted. Needle EMG may increase the concentration of muscle enzymes (CK) in the blood.
If the patient presents with symptoms suggestive of an upper motor neuron lesion (brisk reflexes, abnormal Babinski sign) and/or progressing paraparesis, for example, a neurologist should first assess the situation with appropriate examinations.
Quantitative sensory testing (QST)
QST is used for the diagnosis of small-fibre neuropathy and neuropathic pain.
Measurement of the thermal sensory threshold based on temperature change is usually performed. Other methods, such as ones based on sensing vibration or touch, can also be utilized.
As the tests are based on perception reported by the patient, good cooperative ability and concentration are required.
Evoked potential studies
Evoked potentials (EP) provide information on the functioning of various sensory and central nervous pathway systems.
Typically, somatosensory (sensory evoked potentials, SEP), visual (visual evoked potentials, VEP) and auditory system (brainstem auditory evoked potential, BAEP) studies can be used to examine damage to and dysfunction of the systems.
SEP studies are today mostly used for assessing the prognosis of patients with brain injury.
Diagnosis of organic sleep disorders
Limited overnight polygraphy is usually sufficient for the diagnosis of sleep-disordered breathing in adults and can also be used to detect sleep apnoea and periodic limb movement disorder.
Polysomnography (PSG) should be done in children. EEG should also be included, facilitating sleep staging because breathing changes in the different sleep stages, and the findings should be interpreted in relation to the sleep staging.
A sleep diary is often useful when exploring daytime tiredness and it will also be beneficial when considering the reasons for insomnia. A 2-week sleep diary is normally used before technical investigations.
In actigraphy, the patient's movements and activity are usually monitored over 2 weeks. The obtained information can be used to draw conclusions on disturbed circadian rhythms and disturbed sleep phases.
The Multiple Sleep Latency Test (MSLT) is used to diagnose narcolepsy and hypersomnias.
The Maintenance of Wakefulness Test (MWT) measures the person's ability to remain alert. The test is used to assess how sleep apnoea and other diseases causing disturbed alertness affect the working ability of professional drivers, in particular, and of other people whose work requires a high level of alertness.