Electroencephalography is the measurement of the spontaneous electrical activity of brain. It is non-invasive examination during which tiny small needles are placed under skin, while the animal is in sedation (sleeping) for about 20 minutes. EEG is usually performed in patients with seizures or where seizures are suspected. EEG currently is the only examination which can positively confirm presence of epileptic activity in the brain of the animal and therefore is the most useful in differentiation of the epileptic and non-epileptic events.
Another important role of EEG is in treatment of status epilepticus (continuous seizure) patients. In these cases EEG is the only tool which is able to say objectively if the patient has been treated sufficiently or not as the EEG is showing if the brain has calmed down already or not.
EMG is the recording of the electrical activity of the muscle. During the test the small needle is inserted in to the muscle and the activity recorded. EMG is done on a patient under deep sedation or general anaesthesia therefore no pain is felt during examination.
Normal resting muscle is generally electrically silent. In abnormal muscle there is spontaneous activity and based on the characteristics of this activity, may tell us the kind of process present in the muscle. EMG helps to confirm the of the existence of the disease of the peripheral nervous system and helps to distinguish between primary nerve and muscle disease. It says precisely if the muscle atrophy is because of disease of the muscle or nerve or because of because of too little activity. In case the nerve(s) of the patient have been damaged during trauma episode, the so called denervation potentials will be detectable on EMG 5 days after trauma. The measurement of the denervation potentials in different muscles will tell the examiner which nerves have been traumatized.
Nerve conduction studies
Nerve conduction studies evaluate the function of the peripheral nerves. In the clinical practice, the function of the motor nerves is the most commonly evaluated.
The measurement is done while the the patient is under general anesthesia. Two small needles are inserted near the nerve and the nerve is stimulated with low electrical current. The stimulation of the nerve initiates muscle contraction. Distance from the stimulation to the recording site is measured as well as time needed for impulse to arrive to the muscle. Changes in the nerve conduction velocity indicate damage to the axon of the nerve, to its myelin sheath or both. Nerve conduction velocity helps to confirm the presence of the peripheral nerve disease and to choose the right nerve for the further investigation such as nerve biopsy.
Nerve and muscle biopsies
Nerve and muscle biopsies are often taken at the same time as the electrodiagnostic testing. This is a minor surgery, and typically the patients will go home the same day. Often they will go home on some pain medication for a few days. The biopsies are done so a pathologist who specializes in looking at nerves and muscles can evaluate these organs under a microscope. We will be able to see if there is any infectious or cancerous process occurring. Sometimes, we can tell prognosis from the biopsies as well.