How to diagnose neuropathic pain
Unfortunately, nerve or neuropathic pain and centralised pain conditions occur quite frequently and often remain undetected for a long time. They are accompanied by considerable suffering and severely restrict the quality of life of the affected patients.
Examples of neuropathic pain disorders
- Postherpetic neuralgia
- Accidental nerve injury
- CRPS (Sudeck's disease)
- Chronic back pain
- Painful polyneuropathy in metabolic disorders (e.g. diabetes mellitus)
- Following chemotherapy
- Fibromyalgia / Widespread Pain
In order to identify neuropathic pain symptoms and to find centralised pain symptoms, the examination should look for the following clinical signs:
A painful stimulus (e.g. toothpick) is perceived as significantly more painful.
A stimulus by touch or pricking is perceived less strongly than normally expected.
A stimulus that is actually painless (e.g. touch with a brush or cotton wool) is perceived as painful.
Increased pain sensitivity
Chronic pain often results in increased pain sensitivity, i.e. the sensitivity to pain increases.
IMPORTANT: If possible, the examination should be carried out at the site of maximum (sensory) symptoms - always comparing it to a healthy, unaffected site.
QST - Quantitative Sensory Testing
Nerve pain and centralised pain conditions are identified and diagnosed in a professional setting by means of "quantitative sensory testing" (QST). QST is a psychophysical method for quantifying the functional status of the somatosensory system. QST assesses all types of afferent (sensitive) nerve fibers by applying quantitative and graded stimuli (graded von-Frey hair, multiple pinprick stimuli, pressure algometer, quantitative thermal testing, tuning fork, etc.) using specific testing algorithms. In order to perform a QST correctly, a certain amount of experience and specific equipments are necessary.
Recognize indications of nerve pain easily
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 "tools" of the IISZ - Neuropathic Pain Detection Kit can provide clues to the presence of such a condition:
Toothpick - hyperalgesia search
A toothpick is used to trigger a painful stimulus in a suspected neuropathic painful skin area. If this stimulus is perceived as clearly more painful compared to another, "healthy" skin area, hyperalgesia can be postulated.
Brush - allodynia search
In a presumably neuropathically painful skin area, a brush is used to "paint" the skin and trigger a non-painful sensory stimulus. If the normally non-painful stimulus is perceived as painful, allodynia in the examined area is indicated.
Clothes peg - check pain sensitivity
Long-standing chronic pain disorders often result in increased pain sensitivity. If a clothes peg is clamped to an earlobe for 10 seconds and immediately afterwards the perceived pain intensity is assessed on the "Numeric Rating Scale" NRS (NRS 0 = no pain, NRS 10 = the greatest pain imaginable), the presence of increased pain sensitivity can be evaluated. If the indicated NRS value is >6, an increased pain sensitivity of the central nervous system is suspected.
When is a QST examination recommended?
When there is clinical evidence for a neuropathic pain condition and more precise assessment is needed, QST represents a helpful diagnostic tool. QST makes it possible to distinguish between neuropathic and non-neuropathic pain conditions.
If standard electrophysiological tests appear normal and small fiber neuropathy is still suspected, QST can reveal deficits in sensory nerve fiber function.
In the future, QST could be important for individual patient-specific somatosensory profiling ("sensory phenotyping"). QST could help to identify underlying mechanisms of the pain disorder and to make therapeutic decisions based on a mechanism-oriented anti-neuropathic pain therapy.
Monitor disease progression with QST
QST can monitor sensory deficits over time and is only useful for documenting pain disorders. For example, in patients with (diabetic) polyneuropathy, QST can detect further sensory loss and thus help to prevent potential complications such as diabetic foot ulcers.
Limitations of QST
The QST is a subjective examination. It depends on the attention, motivation, misbehavior, language deficits and cognitive deficits of the examined patient. A QST can only provide a qualitatively good, usable statement if the examined patient cooperates well.
QST has no diagnostic value on 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 bedside examinations, pain questionnaires, sensory nerve conduction velocity studies (electroneurography) and somatosensory evoked potentials.
Backonja MM, Attal N, Baron R, Bouhassira D, Drangholt M, Dyck PJ, et al. Value of quantitative sensory testing in neurological and pain disorders: NeuPSIG consensus. Pain. 2013;154(9):1807-19.
Maier C, Baron R, Tolle TR, Binder A, Birbaumer N, Birklein F, et al. Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): somatosensory abnormalities in 1236 patients with different neuropathic pain syndromes. Pain. 2010;150(3):439-50.
Baron R, Forster M, Binder A. Subgrouping of patients with neuropathic pain according to pain-related sensory abnormalities: a first step to a stratified treatment approach. The Lancet Neurology. 2012;11(11):999-1005
Egloff N, Klingler N, von Känel R, Gander Ferrari M-L, et al. Algometry with a clothes peg compared to an electronic pressure algometer: a randomized cross-sectional study in pain patients. BMC Musculoskeletal Disorders 2011, 12:174