Distal latency describes the time it takes for a nerve signal to travel from the point of stimulation to the muscle or a sensory receiver.
It is an important diagnostic value in electrophysiology and helps with the assessment of nerve conduction velocities.
An increase in distal latency can indicate nerve damage or a condition related to myelin.
How is distal latency measured?
The examination is carried out using an electroneurography measurement (ENG), in which a nerve is stimulated by a weak electrical impulse. This checks how long it takes for the signal to reach its destination. Depending on which nerve is being tested, the normal distal latency is usually in the millisecond range. The measurement is most commonly performed on peripheral nerves such as the median or ulnar nerve.
What does an increased distal latency mean?
A delayed signal can be a sign of nerve damage or a disrupted myelin layer. Myelin is the protective insulating layer around the nerve fibres that allows electrical impulses to be carried quickly. If this layer is damaged, for example due to polyneuropathy or carpal tunnel syndrome, the signal slows down. Inflammation or mechanical pressure on the nerve can also increase distal latency.
When is further investigation needed?
An unusual latency alone is not enough for a diagnosis, but it does provide valuable information. Patients with symptoms such as tingling, numbness, or muscle weakness should receive further examination. The combination of distal latency, nerve conduction velocity, and clinical symptoms allows for a more accurate assessment of possible neurological conditions. Early diagnosis can help to prevent further damage and allow for targeted treatment.
