Central Damage

Question 1

What is spasticity?

Answer 1

[rigidity associated with UMN signs. Under passive movement, it is an encountered resistance that only occurs in one direction of movement, and is velocity dependent. It is also known as ‘clasp knife’ reflex as the resistance melts away once movement exceeds a certain angle (analogous to the resistance encountered opening a pocket knife)]

Question 2

What is spinal shock?

Answer 2

[period of areflexia and flaccid paralysis immediately following spinal (UMN) injury… duration can be hours to weeks]

Question 3

What is polio?

Answer 3

[a virus that appears to kill lower motor neurons only. It used to be a major neuromuscular disease, but thanks to the Salk vaccine is virtually unknown in this country and was on the verge of being wiped off the planet. On an individual basis, it is wildly unpredictable… affecting different motor neuron pools differently. Individuals can have it ‘a little’ or ‘a lot’, with the most affected unable to breathe without assistance.]

Question 4

Do nerves to muscles have sensory fibers?

Answer 4

[Absolutely. On most muscles, half the nerve fibers are sensory. On the other hand, some cranial nerves do not carry sensory input when they leave the brain, but pick it up by the time the get close to the muscle, e.g., the spinal accessory n leaves as pure motor but soon picks up sensory fibers from C3 and C4]

Question 5

What is amytrophic lateral sclerosis (ALS)?

Answer 5

[A neurodegenerative disease typically associated with both upper and lower motor neuron signs. Simultaneous observation of both upper and lower motor signs is indicting (e.g., Babinski + fasciculation). ALS is relatively rare (< .01%), with age being the highest risk factor (~50 on average), affecting slightly more males than females. It is progressive, slowly wiping out both upper and lower motor neurons. For whatever reason, muscles associated with control of the extraocular muscles and urination (Onuf’s nucleus) seem to be the last to go. Diagnosis to death averages 2-5 yr. The NMDA antagonist, Riluzole, has been shown to extend life span up to 6 months.

Question 6

What are peripheral neuropathies?

Answer 6

[Diseases/conditions affecting peripheral nerves (PNS; lower motor neurons). They can be of traumatic or non-traumatic origin. Traumatic are usually mono-neuropathies, with loss of that nerve, and prognosis variable depending largely on condition of tissue between nerve stump and prior target. Non-traumatic neuropathies have various etiologies captured by ‘DANG’, and ‘glove and stocking’ being most frequent distribution of locale. DANG is in decreasing order of frequency: diabetes, alcohol, nutrional, Guillan-Barre. Often noted are that the reflex is gone, and loss includes both sensory and motor loss. Patients will most commonly be areflexic, exhibit fasciculations, with muscle atrophy. Contrast this with myopathies which typically involved proximal muscles, muscle only, intact reflexes, and high levels of creatine phosphokinase (CPK) levels.

Question 7

Distinguish between upper and lower motor neuron signs?

Answer 7

[upper motor neuron signs are typically associated with spasticity, a type of rigidity with a velocity and direction component, hyper-reflexia and Babinski sign. Initial trauma-related loss will also exhibit spinal shock, a varying period (2-8 weeks) of flaccid paralysis and areflexia. This is then replaced by the brisk reflexes, and spasticity. Muscle atrophy is described as ‘atrophy of disuse’. Lower motor neuron signs are arreflexia, fasciculations, and muscle atrophy.]

Question 8

What is the Babinski sign?

Answer 8

[dorsoflexion of the big toe on stroking the plantar surface of the foot from proximal to distal. It is the sine quo non of upper motor neuron damage. It is also normal in babies during the 1st year, reflecting the lack of maturation of the corticospinal tract.]

Question 9

What is spinal ‘shock’?

Answer 9

[Typically observed in spinal injury (upper motor), it is a period in which the muscles distal to the injury exhibit a flaccid paralysis and areflexia. The period is ~2-8 weeks or more. Of significance with loss of lower spinal cord is that bladder is areflexic, necessitating catheter and continuous drainage. The shock period will pass, but even with the reflexive bladder, it is important that complete emptying be monitored. Spinal shock does not occur with near the duration in other animals… likely a statement of the importance of the corticospinal tract in the human]

Question 10

How important are corticonuclear fibers in cranial nerve function?

Answer 10

[absolutely critical. You couldn’t voluntarily stick out your tongue, your jaw wouldn’t work, and you couldn’t talk, for openers. Clinically, because non-lethal damage tends to disrupt corticonuclear (corticobulbar) fibers on one side or the other, the discussion centers on whether a cranial nerve motor nucleus is innervated ipsilaterally, contralaterally, or both. Oculomotor is special, and we covered that. Trigeminal (V) is bilateral, but one observes an unusually brisk jaw-jerk reflex following damage to cortex (representing the mouth) on one side. The facial motor nucleus controlling muscles to the upper face receives bilateral cortical downflow, but that part of the nucleus innervating the lower face receive contralateral influence only (therefore, expect a droop of the right mouth following damage to left cortex). Contrast this with Bell’s palsy, whose most common presentation is upper and lower (and, btw.. the most important clinical issue is keeping the cornea moist due to loss of the orbicularis oculi m). For IX and X, corticonuclear projections (to the nucleus ambiguus, SVE) are contralateral dominant. This can be observed by noting the uvula swings towards the side of cortical damage (loss of muscle tone in uvular muscles opposite cortical damage). Expect issues with swallowing (dysphagia), and articulation of speech (dysarthria, dysphonia, if not Broca’s aphasia, left side). The spinal accessory is ipsilateral dominant. Therefore, cortical damage on the right will yield a shoulder droop to the right and difficulty in turning the head away from the side of cortical damage. The hypoglossal n is contralateral dominant. Therefore, protrusion of the tongue will yield a deviation away from the side of cortical damage (and, it is the loss of power to the genioglosseus that does one in).

Question 11

How is strength rated?

Answer 11

[on a scale of 0-5. On testing, the patient gets 0/5 for no movement, 1/5 for observing twitches, but no movement, 2/5 for movement, but cannot overcome resistance of gravity, 3/5: movement against gravity but cannot overcome imposed resistance, 4/5 movement against some resistance, but weakness noted, and 5/5 is normal.

Question 12

How are reflexes rated?

Answer 12

[The major reflexes are often referred to as ‘deep tendon reflexes’ (DTR) on a scale of 0/4, with a ‘+’ inserted, except at 0. 0 = absent reflexes; 1+ = obvious attenuation, hyporeflexia; 2+ = normal; 3+ = brisk; 4+ brisk, followed by brief clonus (vibration of muscle after reflex); 5+ brisk, with sustained clonus.]

Question 13

What is clonus?

Answer 13

[rapid muscle vibration, which can be phasic (brief) or sustained]

Question 14

What is ‘locked-in syndrome’?

Answer 14

[Rare disorder resulting from infarct of pons that includes bilateral damage to, pyramids (+ corticobulbar), and medial longitudinal fasciculus (MLF). Spared are the central tegmental tract (reticular activating), medial and lateral lemniscus (hearing), spinothalamic and often anterior trigeminothalamic tracts. The individual shows sleep waking cycles on EEG, but can often present as if in coma. Movement is reduced to blinking and vertical eye movements. Not a pleasant condition, and worse, it can often go months before it’s even noticed that the person is conscious, not In a coma]

Question 15

What is the #1 source of peripheral neuropathies in the US?

Answer 15

[type II diabetes, insulin resistant]

Question 16

What are the risk factors for diabetes?

Answer 16

[family history, age, obesity, sedentary life style]

Question 17

Cancer chemotherapy is associated with increased risk of what disorder?

Answer 17

[peripheral neuropathies, especially involving sensory fibers including pain. Of significance is that the neuropathies tend not to appear until several years after the chemotherapy was stopped.]

Question 18

What is multiple sclerosis (MS)?

Answer 18

[autoimmune disorder in which the body produces an antibody for oligodendroglia, the source of myelin in CNS. Average age of onset is 20-30, and affects females/males by nearly 3:1. Relatively rare (~1:20,000 has disease]. The disorder is characterized by episodes of focal neurologic deficits that can include both sensory and motor deficits (e.g., optic neuritis, internuclear ophthalamoplegia). The most common pattern is a focal neurologic issue will emerge, go into remission, and then at another time another focal neurologic issue will emerge (‘separation in time and space’. For many, the duration of the relapse increases over times, shortening the remission phase. There is no cure, but the severity of the attacks can be minimized using interferon and other drugs to suppress T-cells, and, steroids seem to be the treatment of choice (immunosuppressant) during a relapse. Etiology unknown, but there seems to be a link between sunlight, vitamin D (levels of both negatively correlate with the disease), and onset of Epstein-Barrr (EB) virus. In particular, early onset of EB virus, seems to have a protective effect.]

Question 19

Characterize lower motor neuron injury?

Answer 19

[If the lower motor neuron or it’s axon is cut, injury will result in flaccid paralysis, and muscle atrophy. To the extent there are surviving lower motor neurons to that muscle, they will sprout axons and innervate the dennervated muscle fibers resulting in larger motor units (which is evident in the EMG, electromyography. For non-traumatic peripheral neuropathies, it is more common to observe partial denervation of the muscle. A common finding is fasciculations, ‘twitching’ of individual motor units]

Question 20

Characterize upper motor neuron injury?

Answer 20

[Depending on severity, there may an initial ‘shock’ period. This is especially prominent in spinal injury and can continue for 4-8 weeks or more. The shock includes a flaccid paralysis, and areflexia (including an areflexic bladder). This is replaced with a particular form of rigidity, spasticity, and hyperreflexia. Spasticity is a resistance to movement (rigidity) that is directional (extensor or flexor), velocity dependent, and tends to ‘melt’ as passive movement of the limb continues. For involvement of the corticospinal fibers, the Babinski sign is readily apparent as a dorsoflexion of the big toe in response to stroking the plantar side of the foot from heel to toe.]

Question 21

Give examples of peripheral neuropathies?

Answer 21

[Peripheral neuropathies can be traumatic or non-traumatic. Traumatic are localized to site of injury, and include flaccid paralysis with sensory loss as well. Non-traumatic peripheral neuropathies tend to follow a ‘glove and stocking ‘ distribution, with reflexes typically compromised, pain is common, as is ‘tingling’ (paresthesia). Non-traumatic origins include diabetes, alcohol, nutrition, peripheral neuropathies associated with chemotherapy, and Guillan-Barre.

Question 22

What is the prognosis for recovery of function following axotomy of peripheral nerve?

Answer 22

[Reasonable. Following nerve cut, the proximal nerve stumps will sprout growth cones within hours of the injury and try to reach their former target. Success depends on how far the target is, the extent of local trauma (cut with a clean knife fares better than cut via a chain saw), age of individual, disposition of basal lamina (the supporting connective tissue associated with the nerve), and the particular nerve involved (e.g., axons associated with innervating the facial muscles are notorious for getting lost trying to re-find their target). Compression injuries (e.g., from a tourniquet or extremely tight stocking) have a good prognosis because the nerve is still intact all the way to the target… course, a new axon/ dendrite will have sprout and grow.]

Question 23

What is considered a good rate of recovery for peripheral nerve?

Answer 23

[1 mm/day (an inch/month)]

Question 24

What is a ‘nerve graft’?

Answer 24

[A surgical procedure in which a piece of healthy nerve from the person is excised and sewn into place at the site of injury to ‘point the way’ to the target. It is imperative to know that the grafted nerve will die, what the surgeon wants is the basal lamina which will provide a growth track for the recovering nerve]

Question 25

What is spinal shock?

Answer 25

[Refers to the period of areflexia and flaccid paralysis that initially follows massive upper motor neuron injury. It is a given with spinal injury, and may or may not happen with cortical damage alone. The duration of this period is 4-8 weeks or more. Curiously, spinal shock only lasts a few hours in non-primates such as

Question 26

Why don’t cut axons in CNS reestablish contact with their targets?

Answer 26

[they try. Within hours of the cut, they sprout growth cones. However, for unknown reasons, oligodendroglia in the area respond to such events by release factors called collapsins (of which ‘no-go’ is an example) that thwart regrowth by collapsing the growth cones.]

Question 27

Distinguish between fasciculations and fibrillations?

Answer 27

[fasciculations are spontaneous twitching (contractions) of motor units (and visible to the eye), fibrillations are spontaneous twitching of individual muscle fibers (not visible to the eye). Fasciculations are normally common after a demanding workout; otherwise, they tend to be associated with lower motor neuron pathology. Fibrillations are more often than not associated with myopathies.

Question 28

Distinguish between myopathies and neuropathies?

Answer 28

[neuropathies commonly present with weakness of the distal limbs (‘glove and stocking’), with diminished or absent reflex, sensory loss, tingling (paresthesia), and fasciculations. Myopathies present with proximal weakness, no sensory loss, intact reflexes, no tingling, fibrillation (with EMG) and elevated creatine phosphokinase levels (CPK).

Question 29

What are the current interventions in treating spinal injury patients?

Answer 29

[The big shift over the past 20 years is toward stabilizing the patient, but making no efforts to bring down edema at injury site. Stablilizing/immobilization to prevent any further damage is high priority. Beyond that, surgical intervention may be used to remove bone to allow edema to run its course. Gone are efforts to reduce edema via diuretics (e.g., mannitol) and steroids (which reduce edema but are immunosuppressive). The shift in treatment is largely due to evidence that both mannitol and steroids can aggravate natural healing processes.