Examples of neuropathic pain disorders
- Postherpetic neuralgia
- Accident-related nerve injury
- CRPS (Sudeck's disease)
- Chronic back pain
- Painful polyneuropathy in metabolic disorders (e.g. diabetes mellitus)
- After chemotherapy
Clinical signs
In order to identify neuropathic pain symptoms and find centralized pain symptoms, the following clinical signs should be looked for in the examination:
Hyperalgesia: A painful stimulus (e.g. toothpick) is perceived as significantly more painful.
Hypesthesia: A stimulus from touch or pricking is perceived as less intense than normally expected.
Allodynia: An actually painless stimulus (e.g. touch with a brush or cotton wool) is perceived as painful.
Increased sensitivity to pain: Chronic pain often results in increased sensitivity to pain, i.e. the sensitivity to pain increases.
IMPORTANT: The examination should be carried out at the site of maximum (sensory) symptoms if possible - in each case in comparison with a healthy, unaffected site.
How to recognize signs of nerve pain
It is important to know that a QST examination can be useful, but is NOT absolutely necessary to detect a neuropathic pain disorder. The simple “instruments” of the IISZ - Neuropathic Pain Detection Kit can provide clues to the presence of such a disorder:
Toothpick - search for hyperalgesia
A painful stimulus is triggered using a toothpick in a suspected neuropathically painful skin area. If this stimulus is perceived as significantly more painful than in another, “healthy” skin area, hyperalgesia can be postulated.
Brush - search for allodynia
A brush is “smeared” on the skin in a suspected neuropathically painful skin area and a non-painful sensory stimulus is triggered. If this normally non-painful stimulus is perceived as painful, this corresponds to allodynia in the area examined.
Clothespin - check pain sensitivity
Pain disorders that have been chronic for a long time often result in increased pain sensitivity. If you clip a clothespin to an earlobe for 10 seconds and then immediately ask about the intensity of the pain you feel on the “Numeric Rating Scale” NRS (NRS 0 = no pain, NRS 10 = the greatest pain you can imagine), you can estimate whether you have increased pain sensitivity. If the NRS value given is >6, there is a suspicion of increased pain sensitivity in the central nervous system.
Neuropathic Pain Detection Kit
QST - Quantitative Sensory Testing
Nervenschmerzen und zentralisierte Schmerzzustände werden im professionellen Setting mittels einer “quantitativ sensorischen Testung” (QST) gesucht und diagnostiziert. QST stellt eine psychophysische Methode dar zur Quantifizierung des Funktionsstatus des somatosensorischen Systems. QST bewertet alle Arten von afferenten (sensiblen) Nervenfasern durch Anwenden von quantitativen und abgestuften Stimuli (abgestufte von-Frey-Haare, mehrere Nadelstichstimuli, Druckalgometer, quantitatives Thermo Testing, Stimmgabel usw.) unter Verwendung spezifischer Testalgorithmen. Um eine QST korrekt durchführen zu können ist eine gewisse Erfahrung und auch eine spezifische Ausrüstung notwendig.
When is a QST examination recommended?
When clinical evidence of neuropathic pain exists and a more detailed evaluation is necessary, QST can be a helpful diagnostic tool. QST makes it possible to distinguish between neuropathic and non-neuropathic pain conditions.
When standard electrophysiological tests appear normal and suspicion of small fiber neuropathy remains, QST can reveal deficits in sensory nerve fiber function.
Sensory Phenotyping
In the future, QST could be important for creating an individual, patient-specific somatosensory profile (“sensory phenotyping”). QST could help to identify the mechanisms underlying the pain disorder and in the future assist in therapeutic decisions based on mechanism-oriented anti-neuropathic pain therapy.
Monitoring disease progression with QST
QST can monitor sensory deficits over time and is only useful for documenting pain conditions. For example, in patients with (diabetic) polyneuropathy, QST can detect further sensory loss and thus help prevent potential complications such as diabetic foot ulcers.
Limitations of QST
QST is a subjective examination. It depends on the patient's attention, motivation, misbehavior, language deficits and cognitive deficits. A QST can only provide a good, usable result if the patient cooperates well.
QST has no diagnostic value of its own and should be used as an additional diagnostic tool. It must be placed in a broad context and interpreted together with the results of clinical examinations at the bedside, pain questionnaires, studies on the speed of sensory nerve conduction (electroneurography) and somatosensory evoked potentials.
