Chapter 9 - Sensory system evaluation

Questions

Define the following terms:

conscious proprioception, agnosia (stereoagnosia), graphesthesia, dermatome, sclerotome, myotome, radiculopathy, myelopathy, anesthesia/hypoesthesia, hyperpathia, allodynia, hyperesthesia, dysesthesia, paresthesia, polyneuropathy, subjective.
Conscious proprioception is the ability to tell where a body part is in space. It is largely based on joint position sense.
Agnosia (stereoagnosia) is the inability to recognize what a sensation is despite relatively normal perception of the sensation. When it is tactile it is termed sterioagnosia (or asteriognosis). It would be the inability to determine the denomination of a coin despite normal ability to perceive it, for example.
Graphesthesia is the ability to identify letters or figures traced on the skin (without looking).
Dermatome is the area of skin supplied by a nerve root.
Sclerotome is the area of bone and joints supplied by a single nerve root.
Myotome is the muscles supplied by a single nerve root.
Radiculopathy is damage to a nerve root (radiculitis is irritation).
Myelopathy is damage to the spinal cord from any cause.
Anesthesia/hypoesthesia is loss (or decrease) in sensation.
Hyperpathia is the exaggerated perception of normally painful stimuli.
Allodynia is the perception of normally innocuous stimuli as being painful.
Hyperesthesia is excessive sensitivity to any modality.
Dysesthesia is the perception of the pain when no stimulus is present.
Paresthesia is the detection of a sensation in the absence of any stimulus.
Polyneuropathy is generalized damage to peripheral nerves. This is usually due to a systemic cause.
The sensory exam is by definition subjective, that is, relies on the patients report.

9-1. What are the steps involved in the sensory exam?

Answer 9-1. First, the exam needs to determine if the patient can detect modality; next, you need to know if it is the same on both sides; then you need to know if the patient can interpret the sensation.

9-2. How is it possible to lose some types of sensations and not others?

Answer 9-2. Different sensory modalities follow different types of nerve fibers and different pathways (tracts) through the nervous system.

9-3. What sensations are conveyed by the small-diameter sensory nerve fibers in a peripheral nerve?

Answer 9-3. Small, unmyelinated or lightly-myelinated (slow) nerve fibers convey pain and temperature sense.

9-4. What sensations are conveyed by large-diameter sensory nerve fibers in a peripheral nerve?

Answer 9-4. Large, heavily myelinated (fast) nerve fibers convey proprioception and well-localized touch sensation. They are also the sensory limb of the muscle stretch reflex.

9-5. What sensations are conveyed by the dorsal columns?

Answer 9-5. Dorsal columns convey vibration, 2-point discrimination and joint position sense.

9-6. What sensations are conveyed by the spinothalmic tract?

Answer 9-6. The spinothalamic tract conveys pain, temperature and very light (poorly localized) touch.

9-7. What is tested by double simultaneous stimulation?

Answer 9-7. Double simultaneous stimulation tests attention/neglect (parietal lobe).

9-8. Where would the lesion be if the patient was able to detect all modalities of sensation but could not recognize an object placed in the right hand?

Answer 9-8. The left parietal lobe (somatosensory association area).

9-9. What is the common sensory loss from damage to the spinal cord?

Answer 9-9. Spinal cord lesions often result in sensory level (loss of sensations below lesion) due to damage to ascending sensory tracts. This loss (especially of pin-prick sensation) usually begins at least several segments below the level of the lesion of the tract.

9-10. What would be the expected sensory loss from damage restricted to the left side of the spinal cord?

Answer 9-10. There would be ipsilateral loss of vibration and joint position sense and contralateral loss of pain and temperature sense below the level of the lesion. The pain and temperature sense loss would start at least several dermatomes below the injury.

9-11. What is the characteristic of sensory loss due to damage of peripheral nerves in a limb?

Answer 9-11. Peripheral nerve injury (mononeuropathy) usually results in well-localized sensory loss (often with appropriate motor loss).

9-12. What is the pattern of sensory loss seen in diffuse damage to peripheral nerves (polyneuropathy)?

Answer 9-12. Diffuse peripheral nerve injury (polyneuropathy) results in stocking (and, later, glove) sensory loss.