Clinical examination

All patients should have a general physical and neurological examination. Sensory abnormalities can be specifically assessed and quantified using simple bedside equipment (Figure 11.1). A bedside sensory examination most commonly includes examination of pinprick, touch, cold, heat, and vibration sensation. Touch is examined by gently touching the involved skin area with a cotton swab. It is important to distinguish between dynamic stimuli in which the area is stroked and a static stimulus in which

Figure 11.1 Bedside equipment for analyzing sensory function in humans: metal thermorollers (kept at specific temperatures), von Frey hair, cotton wool, brush, pinprick roller, two-point discriminator, and a visual analog scale (VAS) meter.

the skin is exposed to a static, i.e. a nondynamic, stimulus. Cold and warm sensations are recorded by measuring the response to a specific cold or warm thermal stimulus, e.g. thermorollers maintained at 20 and 40°C, respectively. Cold sensation can also be assessed by the response to a drop of acetone on the skin. Vibration is assessed by a tuning fork placed at strategic points (malleoli, interphalangeal joints). At present, there is no consensus about the site where such activity should be measured, but it is generally agreed that this is best performed in the area with maximal abnormality using the unaffected contralateral mirror image skin area as control. However, this needs to be qualified by understanding that some studies have described contralateral segmental sensory abnormalities following a unilateral nerve or root lesion. An examination of the mirror image area of a nerve injury may therefore not represent a true control, but without a body of validated "normal values'' for the various psychophysical modalities this appears to be the best option at present. For all types of stimuli, the response can be graded simply as:67

If the response is hyperesthetic, it is classified as dyses-thetic (unpleasant abnormal sensation to a stimulus), hyperalgesic (increased response to a normally painful stimulus), or allodynic (pain evoked by a normally non-painful stimulus). A correlation between spontaneous pain and sensory response in the painful area suggests that the two phenomena are reflections of the same mechanism: a central sensitization of dorsal horn

neurons. ,

An essential point concerns the detailed description of what the sensory abnormalities reflect: does the distribution correspond to the innervation territory of a sensory nerve, to fascicles, to roots, to cord segment, or to a cerebral structure? This is not always an easy task and may require detailed neurological knowledge. However, this is important because a distinction has to be made between the sensory abnormalities seen in, for example, somatization disorders and those seen in diseases of the nerves or CNS.

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