Changes in sensation are some of the most common neurological symptoms in hospitalized patients. Patterns of weakness is covered in Chapter 28. In this chapter, we will survey an approach to evaluation of sensory changes. Most of the causes of isolated changes of somatosensory sensation are relatively benign or do not require hospital admission. In some situations, an etiology for such findings confined to sensation may not even be found. Conversely, sensory deficits that are associated with other neurological findings that point to specific neurological regions are clearly based on organic pathology, deserve attention, and help in localizing the lesion.
Clinical examination of the sensory system may be the most difficult part of the neurological examination because of the “psychophysical” nature of the tests employed; the stimuli applied are not standardized or quantified, and the findings are elicited by the nature of a judgmental response from the patient regarding the stimulus. This results in significant variability both within and among examiners in terms of the precise stimulation given, as also variability among even normal subjects provided the same type of stimulus. It is best to perform the sensory examination late in the neurological evaluation when one already has some idea as to the kind of sensory abnormality one may expect in the context of the patient’s presentation.
PART 1—PERIPHERAL SENSORY SYNDROMES
A 45-year-old obese woman presents with tingling and numbness of the left anterolateral thigh. The patient has researched her symptoms on the internet and is now worried that she may have multiple sclerosis. You are asked to evaluate the patient in the emergency department (ED). One of the ED residents asks for advice regarding how to perform the sensory examination.
What factors determine the rate of detection of stimulus in sensory testing?
Several factors determine the detection of a stimulus:
The strength of the stimulus: Stronger stimuli are easier to detect.
The size of the area where the stimulus is applied: Applying the stimulus to larger skin areas makes it easier to detect the stimulus due to spatial summation.
Duration of the stimulus: Applying the stimulation for a longer time makes it easier to detect the stimulus (temporal summation).
How does one vary the strength of the stimulation during the examination?
At the outset, the best strategy is to use the lightest stimulus strength, applied to the smallest possible area, and for the least possible time to be able to detect the mildest of sensory loss. With such a strategy, if several stimuli are applied to an area, subjects with lesions of the somatosensory system consistently miss a larger number of stimuli as compared to persons with normal sensation.
If a deficit is demonstrated then the stimulus parameters are strengthened (increased strength, increased ...