Quantitative sensory testing

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Quantitative Sensory Testing (QST) is a diagnostic method used to evaluate the function of sensory nerves. It provides a quantitative measure of sensory nerve function in patients, which can be useful for diagnosing and monitoring neuropathies, chronic pain conditions, and other disorders affecting the sensory nervous system. QST involves a series of tests that measure responses to stimuli such as vibration, pressure, cold, and heat. These tests can help identify sensory deficits and their severity, offering valuable information for treatment planning.

Overview

Quantitative Sensory Testing is a non-invasive method that assesses the function of small and large sensory fibers. It is based on the application of stimuli at varying intensities to determine the sensory threshold, which is the minimum intensity at which a stimulus is perceived. The tests can be performed using various devices, including vibrometers for vibration thresholds, algometers for pressure pain thresholds, and thermal testers for cold and heat detection thresholds.

Clinical Applications

QST is widely used in clinical settings for the diagnosis and management of various conditions, including:

• Peripheral neuropathy: QST can help in the early detection of neuropathies, often before symptoms become apparent.
• Diabetes: Diabetic neuropathy is a common complication of diabetes, and QST can be used to monitor sensory function over time.
• Fibromyalgia and other chronic pain syndromes: QST can help in understanding the altered sensory processing in these conditions.
• Complex regional pain syndrome (CRPS): QST can assist in the diagnosis and monitoring of CRPS by identifying sensory abnormalities.

Procedure

The QST procedure typically involves the following steps: 1. Calibration of the testing device. 2. Selection of the test site, usually on the skin of the hands or feet. 3. Application of stimuli in increasing intensities until the patient perceives the sensation. 4. Recording of the threshold at which each type of stimulus is detected.

Patients are usually seated in a comfortable position, and the test environment is controlled for temperature and other factors that might affect sensory perception.

Advantages and Limitations

Advantages:

• Non-invasive and relatively easy to perform.
• Provides objective data on sensory nerve function.
• Can detect sensory deficits not identifiable through clinical examination alone.

Limitations:

• Requires patient cooperation and understanding of the test procedure.
• Results can be influenced by psychological factors and the testing environment.
• Not suitable for all patients, including those with severe cognitive impairments.

Conclusion

Quantitative Sensory Testing is a valuable tool in the assessment of sensory nerve function. It offers a detailed understanding of sensory deficits, aiding in the diagnosis and management of various neuropathic conditions. Despite its limitations, QST remains an important part of the neurological assessment, providing insights that can guide treatment decisions and improve patient outcomes.