Guidelines2,13-15 recommend a structured approach, with patient history and clinical examination being the most important parts of the diagnosis. Neuropathic pain can be graded as possible, probable or definite based on the built-up evidence. Treatment can be commenced once probable neuropathic pain has been diagnosed,14 with further investigations only considered if these tests would inform treatment.
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History is needed to reach a ‘possible’ level of certainty.14
A history suggestive of a relevant neurological lesion (like herpes zoster or a traumatic nerve injury), pain descriptors (burning, shooting, pricking and pins and needles) or the presence of non-painful sensations like numbness or tingling are suggestive of neuropathic pain.14 Furthermore, the pain distribution should be explainable by a lesion or disease in the somatosensory system, or be typical of an underlying neuropathic disorder14 (see Figure 1). Validated assessment tools14,15,25-30 have been created to help in this assessment, but should not be used alone.14
A clinical examination is needed to reach a ‘probable’ level of certainty.14
Once the history suggests a possible diagnosis of neuropathic pain, tools such as toothpicks, brushes or cotton wool can be used in a clinical examination to detect clinically consistent sensory changes that help further differentiate neuropathic from non-neuropathic pain.2,13-5 Hypoalgesia to pinprick, hypoesthesia to tactile stimuli and allodynia to brush and cold are particularly discriminant.13,31 Sensory changes should also lie within a plausible neurological distribution (see Figure 1).
Confirmatory tests can be considered in order to reach a ‘definite’ level of certainty14 if these tests would inform treatment. A ‘definite’ level of certainty is commonly not required in primary care.
Tests must confirm that a lesion or disease of the somatosensory system can explain the pain.2,13-15 These include magnetic resonance imaging (MRI) to confirm a stroke, multiple sclerosis or spinal cord injury and a skin biopsy showing reduced nerve fibre density.14