Somatosensory testing is a diagnostic procedure that evaluates the function of the somatosensory system. This system processes sensory information from the body, including touch, temperature, pain, vibration, and proprioception, the sense of body position and movement. These tests show how well sensory signals transmit from the body to the brain, helping understand various neurological conditions.
Understanding the Purpose of Somatosensory Testing
Somatosensory testing pinpoints and assesses damage or dysfunction within the peripheral nerves, spinal cord, or brain. It helps identify conditions like neuropathies (e.g., diabetic neuropathy, carpal tunnel syndrome), spinal cord injuries, multiple sclerosis, and stroke. They also evaluate other neurological disorders affecting sensation or motor control. By examining signal transmission speed and strength, these tests precisely locate nerve damage.
Common Types of Somatosensory Tests
Several types of somatosensory tests measure specific aspects of nerve function. Nerve Conduction Studies (NCS) measure how quickly electrical signals travel along a nerve. Electrodes are placed on the skin over a nerve, delivering a small electrical impulse and measuring the time for the signal to reach another electrode.
Somatosensory Evoked Potentials (SSEPs) measure electrical activity in the brain and spinal cord from sensory stimulation. Mild electrical impulses are delivered to a nerve (typically in an arm or leg), and electrodes on the scalp and spine record the brain’s and spinal cord’s electrical responses. Signal travel time from the stimulated nerve to the brain indicates sensory pathway integrity.
Quantitative Sensory Testing (QST) assesses a patient’s ability to perceive and respond to sensory stimuli. This involves applying temperatures, vibrations, or pressures to the skin to determine sensory thresholds. QST helps evaluate nerve integrity and function, providing objective measurements.
Preparing for and Undergoing the Test
Preparing for somatosensory testing involves a few steps for accurate results. Patients are usually advised to avoid lotions or creams on the skin where electrodes will be placed, as these can interfere with electrode adherence. Wearing comfortable, loose-fitting clothing is also recommended, and individuals should inform their doctor about any medications they are taking. Certain substances like caffeine may need to be avoided for a few hours prior to the test.
During the test, the patient will typically be in a quiet room, often reclining in a comfortable chair or lying down. Small electrodes will be taped to various body parts (scalp, arms, legs, or back), depending on the specific test. Patients might experience mild electrical impulses, a sensation of pressure, or changes in temperature, but these are generally well-tolerated and temporary. The duration of the procedure can vary, but most tests are completed within 30 minutes to two hours.
What Test Results Indicate
Somatosensory test results are interpreted by comparing them to normal ranges. Abnormal results can point to nerve damage, demyelination (damage to the protective covering of nerves), or problems within the spinal cord or brain. These findings help healthcare professionals localize the specific area of concern within the somatosensory pathway.
Results represent one piece of the diagnostic puzzle. They are typically reviewed in conjunction with a patient’s reported symptoms, their complete medical history, and findings from other diagnostic tests, such as imaging scans. A healthcare professional integrates all this information to arrive at a comprehensive diagnosis and to develop an appropriate treatment plan.