The Sensitive Nervous System Chapter IX: Manual Assessment of Nerve Conduction

This is a summary of Chapter IX of “The Sensitive Nervous System” by David Butler.

The Value

The neurological exam is an excellent way to sample the patient’s nervous system. When looking at the neurological system, we must realize that testing does not reflect a tissue injury alone. It demonstrates the neurological pathway’s response. There is no such thing as a focal lesion in the nervous system.

We must also understand that the exam is a very small component of a further comprehensive assessment, providing moderate diagnostic value at best. Sensitivity for a screen like this is inherently poor, meaning this examination cannot rule out nervous system pathology or involvement.

Sensory Examination

If we are going to walk the neurological walk, we first need to talk the neurological talk. Here are some important definitions.

  • Allodynia: Pain from a non-painful stimulus.
  • Hyperalgesia: Increased response to a painful stimulus.
  • Analgesia: No pain from a painful stimulus.
  • Hyperpathia: Abnormal pain reaction to a repetitive stimulus.
  • Hypoalgesia: Decreased response to a painful stimulus.
  • Hypoesthesia: Decreased sensitivity to a stimulus.
  • Hyperesthesia: Increased sensitivity to a stimulus.
  • Dysesthesia: Unpleasant, but not painful response to a stimulus.

First, we will take a look at dermatomes. Now depending on who you talk to, dermatomal levels will be different. Moreover, many people have anatomically variant dermatomes, and often times these can fluctuate throughout the day. There are however, some signature zones that are fairly consistent throughout the literature.

There are several different sensations that need to be tested. Make sure the responses include yes, no, and don’t know.

  • Light touch: Using a tissue, piece a cotton wool, monofilaments. It is better to use these than hands so you can be consistent. You can also just touch someone’s body hair if you are working with a hairy individual.
  • Superficial pain: Sharp object, dull object.
  • Hot/cold.
  • Deep pain: Often the movement exam is enough, but the Achilles can also be squeezed.
  • Proprioception: Finger to nose, or nose to the clinician’s finger in a constantly changing position.
  • Vibration.

The above areas target predominantly peripheral sensation, but we can also test the cortical sensory capabilities.

  • Graphesthesia: Identify a letter or number written on the skin.
  • Finger identification: Touch a patient’s finger followed by the patient touching that same finger.
  • Stereognosis: Identify objects by handling it.
  • Two-point discrimination: Tell the difference between two points and one point. Here are the distances between two points that normally can be discriminated.
    • Finger tips: 2-7 mm.
    • Palms: 8-15 mm.
    • Back of the hand: 20-30 mm.
    • Top of the foot: 30-40 mm.
    • Back: 40-80 mm.

Motor Function

There are several ways to assess motor function.

  • Muscle wasting.
  • Tremors/fasiculations.
  • Manual muscle test: Palpate tendons while resisting to assess springiness.
  • Quick manual muscle test.
    • Median Nerve: OK sign.
    • Ulnar nerve: Froment’s sign.
    • Lower limb: Heel/toe walk.
Median nerve is a-OK.

Reflexes

Reflex testing looks at afferent connections and general nervous system sensitivity. However, reflexes have no correlation with muscle strength or tendon response. As a general rule, if there is reflex loss with certain conditions, prognosis is generally poorer.

  • Muscle-stretch reflex testing: Only until a response is elicited. There is no rationale as to why a response might fatigue.
  • Superficial skin: An example would be the abdominal or cremasteric reflex (look that last one up).
  • Central reflexes: Clonus or Babinski

Here is an example of clonus

And Babinski, normal response first.

A positive Babinski  a.k.a. punt ASAP.

Cranial Nerves

Here is a list of how to test each cranial nerve.

  • Olfactory (I): Smell identification.
  • Optic (II):  Reading a sign with letters 20 ft away.
  • Oculomotor, trochlear, and abducens (III, IV, VI): Eye tracks finger movements.
  • Trigmeninal (V): Facial sensation; biting.
  • Facial (VII): Facial symmetry. Lower motor neuron lesions affect entire side of face (Bell’s Palsy). Upper motor neuron lesions affect only the lower face (stroke).
  • Vestibulocochlear (VIII): Hearing & balance.
  • Glossopharyngeal (IX): Gag reflex, numbness in back of throat.
  • Vagus (X): Swallowing.
  • Spinal Accessory (XI): Shoulder shrug.
  • Hypoglossal (XII): Tongue deviates toward affected side.

Autonomic Nervous System (ANS)

Observation is an important way to test ANS function. One thing to look for is Horner Syndrome, which includes the following signs/symptoms on one side.

  • Miosis (pupil constriction).
  • Ptosis (drooping of upper eyelid).
  • Enopthalamus (eye retracted in the orbit).
  • Anhydrosis (Lack of sweating).
No, she’s not winking brah.

There is also a reverse Horner syndrome, which is a sympathetic irritation rather than paralysis.

  • Pupillary dilation.
  • Hyperhydrosis (increased sweating).
  • Facial flushing.

Another way to check the ANS is by skin palpation. Here you want to look for redness, sweating, and trophic changes (pitting edema, shiny skin, nail clubbing).

Not this type of clubbing.

Nerve Root Rules

Here Butler presents which is probably the easiest way to learn innervations that I have ever seen. Why didn’t I learn this in PT school? Let’s break the rules down by area.

The Trunk

  • Nerve roots follow cutaneous fields (know your dermatomes).
  • Nipple level is T4.
  • Belly button is T9.

The lower limb

  • Everything starts at L2.
  • Muscles at each joint have 4 nerve root innervations.
    • Hips are L2-L5.
    • Knee is L3-S1.
    • Ankle is L4-S2.
    • Front muscles are innervated before back muscles with 2 apiece.
      • Take the knee. Quads are L3-L4, hamstrings are L5-S1.
      • In before out.
        • Inversion is L4, eversion is L5-S1.

The Upper limb

  • The shoulder is C5-C8.
  • The shoulder innervates asymmetrically.
    • C5 is abduction.
    • C6-8 is adduction.
    • Elbow is C5-6 for flexion, C7-8 is extension.
    • Down the arm drop a root, but only 2 roots per joint.
    • Small hand muscles are T1.
After learning innervations this way, I can empathize.
After learning innervations this way, I can empathize.