Localization of Motor Diseases

Question 1

Lateral Corticospinal Tract (LCST):

• Function:
• Lesion:

Answer 1

• Function:
  
  • movement of contralateral body
• Lesion:
  
  • contralateral weakness

Question 2

It takes at least _ neurons to transmit impulse from cortex to muscle

Answer 2

2 neurons:

1. **UMN: **originating from primary motor cortex that synapses onto LMN
2. **LMN: **in the ventral horn of the spinal cord
   
   • α-motor neuron

Question 3

To localize lesions further along LCST look for:

Answer 3

1. Contralateral weakness & aphasia, apraxia, neglect or other cortical sign ⇒ lesion in cortex
2. Contralateral weakness & ipsilateral CN deficits ⇒ lesion in brainstem
3. Bilateral weakness below a certain spinal level ⇒ complete spinal cord lesion at that level
   
   • Ipsilateral hemibody weakness & **contralateral hemisensory deficit below a spinal level **⇒ lesion of hemicord (Brown-Sequard syndrome)

Question 4

Corticobulbar tract:

• Function:
• Lesion:

Answer 4

• Function:
  
  • **Controls contralateral facial movement **
• Lesion:
  
  • ​contralateral weakness

Question 5

UMN pattern of facial weakness:

Answer 5

lesion of corticobulbar tract

• contralateral weakness of lower face
  
  • facial droop, drooling, weak smile
  • intact forehead wrinkle
• forehead spared due to bilateral cortical input to upper face

Question 6

LMN pattern of facial weakness:

Answer 6

lesion of facial nucleus or facial nerve

• ipsilateral weakness of upper & lower face
  
  • facial droop, inability to close eye
  • no forehead movement

Question 7

Reticulospinal tract:

Function

Answer 7

• Unconscious motor control & for giving your muscles ‘tone’
• LMNs are tonically active ⇒ INHIBITED by the reticulospinal tract
• ↑UMN (specifically the reticulospinal tract) activity ⇒ inhibits LMN ⇒ muscle relaxes
• ↓UMN activity ⇒ loss of inhibition of LMN ⇒ muscle contracts
• Antigravity muscles are more tonically active than muscles that move in the plane of gravity

Question 8

Lesion of reticulospinal tract:

Answer 8

• Acute lesion ⇒ contralateral hypotonia
  
  • acute stroke
• Chronic lesion⇒contralateral hypertonia
  
  • chronic stroke
• ​​UMN pattern of weakness (chronic):
  
  • due to increased tone in antigravity muscles
  • see flexion at elbow/fingers/wrists, knee extension, ankle plantarflexion, ankle inversion, hip adduction

Question 9

Reflexes:

• Hyperreflexia:
• Hyporeflexia:

Answer 9

• Hyperreflexia ⇒ UMN lesion
• Hyporeflexia ⇒ LMN lesion or lesion of afferent or efferent limb

Question 10

Anterior horn cell lesion:

Answer 10

• Signs: flaccid paralysis, severe muscle atrophy, fasciculations, cramping, loss of reflexes
• fasciculation (α-motor neuron lesion)
  
  • ​spontaneous firing of motor neuron
  • can see ‘twitching’ of muscle under skin
  • not painful
• cramping
  
  • firing of mutiple motor neurons or entire muscle
  • usually causes entire muscle to contract
  • painful
• Ex: ALS, polio

Question 11

Root lesion:

Answer 11

shooting pain in a root dermatomal distribution

• loss of reflexes that corresponds to root
• little or no weakness & atrophy
  
  • in order to have muscle atrophy due to root lesion ⇒ all roots to that muscle need to be lesioned
• Ex: disc herniation

Question 12

Plexus lesion:

Answer 12

lesion of lumbosacral or brachial plexus

• multiple muscles in an arm or leg are weak
• sensory loss & loss of reflexes usually well defined
  
  • depends on location of lesion
• usually painful

Question 13

Plexus Lesion:

Erb’s palsy

Answer 13

due to lesion of upper trunk of brachial plexus

• arm is held internally rotated, extended at elbow, flexed at wrist at side of body
• characteristic “waiter’s tip” pose

Signs & Symptoms:

1. loss of arm abduction ⇒ axillary nerve; C5 & suprascapular nerve; C5/6
2. loss of elbow flexion ⇒ musculocutaneous nerve; C5/6
3. loss of external rotation of humerus ⇒ suprascapular nerve; C5
4. loss of wrist extensors ⇒ radial nerve; C6
5. Can have sensory loss, as well as loss of biceps & brachioradialis reflexes
6. NOTE: Movements of fingers are spared because they are innrvated by the lower brachial plexus

Question 14

Plexus Lesion:

Klumpke’s palsy

Answer 14

lesion of lower trunk of brachial plexus

• Opposite symptoms of Erb’s palsy
• Weakness in fingers but no difficulty moving across shoulder & elbow
• Weakness of all ulnar innervated muscles, median innervated hand muscles, radially innervated extensor digitorum communis (extends fingers)
• May have an ipsilateral Horner’s syndrome due to sympathetic fibers traveling from T1 cord ascending to superior cervical gangion
• Can be caused by birth trauma or any other trauma

Question 15

Plexus Lesion:

Pancoast tumor

Answer 15

lesion of lower trunk of brachial plexus due to tumor infiltration

• usually by apical lung tumor
• symptoms depend on extent of infiltration
• affects lower trunk first (like Klumpke’s)

Question 16

Peripheral nerve lesion:

Answer 16

muscles innevated by that nerve are affected

• can be associated with profound atrophy
• dense sensory loss in the distribution of peripheral nerve
• reflexes may be lost if muscle being tested is innervated by lesioned nerve

Question 17

Peripheral nerve lesion:

Carpal Tunnel Syndrome

Answer 17

median nerve compression at wrist (neuropathy)

• overuse of finger flexors from repetitive tasks cause these muscles to hypertrophy
• hypertrophied muscles & median nerve pass through a tunnel (called carpal tunnel)
  
  • bound by a thick ligament called transverse carpal ligament
• muscles compress the nerve as they grow

Signs & Symptoms

1. pain and tingling in median region of hand (thumb to lateral half of ring finger)
2. especially bothersome at night
   
   • hand gets accidently hyperflexed at wrist & pt wakes up and shakes out hand
3. if chronic, cause cause atrophy of median innervated hand muscles causing loss of bulk of thenar eminence

Question 18

Neuromuscular junction defect:

Answer 18

fatigable weakness

• worse later in the day & after repetitive movement
  
  • improved strength after rest
• no sensory loss
• reflexes usually normal
• no muscle atrophy

Question 19

What muscles do NMJ defects affect?

Answer 19

Affects muscles that are constantly working:

• Levator palpebrae (raises eyelid) ⇒ ptosis
• Extraocular muscles ⇒ diplopia
• Neck extensors ⇒ dropped head
• Core muscles ⇒ difficulty rising from chair, stairs
• Swallowing muscles ⇒ dysphagia
• Intercostals/diaphragm ⇒ difficulty breathing
• Eg. myasthenia, Lambert-Eaton myasthenic syndrome, botulism

Question 20

Muscle lesion:

Answer 20

weakness confined to certain muscle groups

• sensation preserved
• slowly progressive weakness (not fatigable)
• reflexes are normal (profound muscle atrophy can result in areflexia or hyporeflexia)
• Muscle can degenerate due to:
  
  • inflammation (myositis)
  • genetic defect
    
    • muscular dystrophy like Duchenne muscular dystrophy

Question 21

CASE: 31 yo F developed sudden R f/a/l weakness 2 weeks ago. She has mild slurred speech & has been falling. She denies numbness & headache.

Exam:

• Normal language; no neglect ⇒ no cortical signs & leg involved (so 2 vascular territories involved)
• ↓R nasolabial fold ⇒ L corticobulbar tract (before pons)
• ↑tone in R arm; R finger taps slow & 4+/5 strength in R arm/leg ⇒ LCST on L lesioned
• Reflexes 3+ on R arm/leg ⇒ L LCST lesioned
• Spastic gait ⇒ indicative of corticospinal injury

Answer 21

• Lesion: L LCST & L corticobulbar tract at internal capsule or L pons
  
  • ​i.e. L posterior limb of internal capsule
• Cause(s): stroke or multiple sclerosis

Question 22

CASE: 62 yo F with DM, HTN develops sudden aphasia and R face/arm weakness.

Exam:

• Speech is halting, effortful, agrammatic, few words ⇒ Broca’s aphasia ⇒ L frontal cortex (a cortical sign & hence lesion in cortex)
• L gaze preference ⇒ R frontal eye fields are working & L FEF are NOT ⇒ another cortical sign
• R lower facial weakness & R arm drift; leg normal ⇒ L LCST in face & arm ⇒ L frontal lobe (leg is medial frontal lobe, which is not in MCA territory)
• Reflexes: absent in RUE; normal elsewhere; Babinski absent on L and mute on R ⇒ reflexes are low immediately after stroke & Babinski has not evolved yet; it takes at least 1-2 weeks for hyperreflexia & spasticity to develop after a lesion to UMN

Answer 22

• R face/arm sensory deficit ⇒ L parietal somatosensory cortex
• Lesion: L frontal & parietal cortices (MCA distribution)
• Causes: stroke

Question 23

CASE: 22 yo F develops neck pain, vertigo, ataxia, L sided facial numbness after chiropractic manipulation.

Exam:

• • R beating horizontal nystagmus on R gaze, N/VL cerebellar pathways or vestibular nuclei
• • L V1-V3 ↓ PP sensationL trigeminal nucleus & tract
• • Hoarse voice & ↓palate elevation L, ↓gag on LL nucleus ambiguus &/or CN 10lesion in medulla
• • No weakness
• • L FTN ataxia on hands/feetL inferior cerebellar peduncle
• • R ↓PP on bodyL spinothalamic tract
• • L Horner’s syndrome (ipsilateral ptosis, miosis, anhidrosis)L descending hypothalamic fibers

Answer 23

• Notice absence of cortical signs
• Notice **crossed signs: **L face & R body reduced sensation ⇒ places lesion in brainstem

o

• Since cranial nerves on L are affected ⇒ should be L brainstem involved
• Lesion: left lateral medulla (supplied by L vertebral artery)
  
  • Wallenberg syndrome
• Cause: vertebral dissection secondary to chiropractic manipulation (rapid rotation of neck ⇒ layers of artery to separate ⇒ ‘dissection’) ⇒ causes blood in lumen to enter b/w the layers & causes a clot to form ⇒ no blood flows through that vessel ⇒ stroke

Question 24

CASE: 62 yo M with HTN has 2 days of R f/a/l numbness.

Exam:

• Normal language
• R face↓ PP/temp
• Normal body/facial strength
• Reflexes normal
• R body ↓PP/vibration/temp
• No neglect

Answer 24

• Lesion: L thalamus
  
  • receives STT and dorsal column/medial lemniscus afferent information from both body & face
• Cause: stroke

Question 25

CASE: 38 yo M working in a Cola factory has R thumb, index & middle finger pain & tingling x 2 month, especially at night.

Exam:

• Decreased PP in R index, middle, thumb ⇒ region too localized to be cortex or thalamus; so, most likely a peripheral lesion
• Weakness in R opponens pollicis & reduced bulk in thenar eminence ⇒ these muscles are done by median nerve
• Reflexes normal

Answer 25

• Localize: right median nerve
• Cause: median neuropathy at the wrist
  
  • Carpal Tunnel syndrome

Question 26

CASE: A patient falls from a tree and develops L sided weakness.
Exam:
• No weakness in hand
• L lateral forearm ↓PP
• Reflexes: L biceps, brachioradialis 1+

Answer 26

• Localize: L upper trunk of brachial plexus
• Cause: usually related to trauma in which angle between shoulder & neck is rapidly increased, causing tearing of upper portion of brachial plexus
  
  • lesion could be in the trunk or roots
  • if lesion was at level of roots, there may be shooting pain down arm
  • additional studies (like EMG) need to be done to confirm clinical suspicion