How to examine a person with suspected neuropathic pain?
The examination of a person in chronic pain should begin with an appropriate general physical examination of the affected area. Thus a musculoskeletal examination (visual inspection and palpation of the joints, range of motion testing, and firm palpation of tendons and fasciae for recognized musculoskeletal conditions, such as extensor tendinitis or plantar fasciitis) is important. Next, examination of the skin and soft tissues for trophic changes, color changes, evidence of vascular insufficiency, and edema is important, especially if CRPS is suspected. It is important not to neglect these fundamental aspects of the general physical examination.
A comprehensive neuromuscular examination, including sensory, motor, and reflex testing, is important if neuropathic pain is suspected. The goal is, in part, as it is in evaluating other neurological problems: Is there evidence of a neurological deficit, and if so, what is the localization?
The sensory examination should explicitly include the following:
- • Large fiber modalities: Typically light touch and vibration; position sense testing is unlikely to be revealing unless vibration perception is substantially impaired.
- • Small fiber modalities: Typically perception of pinprick and temperature. Only one of these may be sufficient, and testing of pinprick perception is generally better at identifying the margins of the symptomatic area.
Particular attention should be paid to the presence of sensory disturbances other than sensory loss alone. These can include:
- • Allodynia: Light stroking of the skin with cotton or a fingertip might demonstrate allodynia (a painful perception in response to a non-noxious stimulus). This is particularly prevalent and severe, for example, in PHN, and can be present in PTNs and painful small fiber neuropathy.
- • Hyperalgesia: Testing with a pin may evoke excessive pain, and often a person with hyperalgesia will withdraw promptly as one approaches with the pin to guard the region, or will refuse pinprick testing. Sometimes, in distal symmetric painful polyneuropathy, the distal zone of sensory loss abuts a zone of hyperalgesia, which in turn yields to normal sensation as one moves proximally.
- • Other dysesthesias: At times people with neuropathic pain report other abnormal and unpleasant responses to external stimuli, or a delayed or lingering perception after the stimulus is removed. Because they are inconsistent with expectations of normal physiologic responses, patients themselves sometimes discount such sensations, but they can be indicators of a neuropathic process.
- • Profound sensory loss: When this occurs in a painful area, consider the possibility of a deafferentation pain. The clinical context should be informative in this regard.
In the case of a possible posttraumatic neuropathy, explore the course of the nerve for the presence of a Tinel’s sign.