Weakness COPY Flashcards
Describe broadly the areas where neuromuscular weakness can originate
1) CNS
2) PNS
3) Neuromusuclar junction
4) myofibers
Discuss causes of nonneurological generalized weakness
Alteration in plasma volume (dehydration)
Alteration in plasma composition (blood glucose, electrolytes)
Derangement in circulating red blood cells (anemia or polycythemia)
Decrease in cardiac pump function (MI)
Decrease in systemic vascular resistance (vasodilatory shock)
increased metabolic demand (local or systemic infection, endocrinopathy, toxin)
Mitochondrial dysfucntion (severe sepsis or toxin mediated)
global depression of the CNS (sedatives, stimulant withdrawals)
Where are the anatomical origins of lower motor neurons
Peripherally the spinal nerves extend from the anterior horn of the spinal cord
Describe symptoms of UMN lesions
Spaciticity to extension in the upper extremities and to flexion in the lower extremities
Hyperreflexia
Hoffmans sign – middle finger is held loosely then flicked down, positive if the thumb flexes and adducts
Babinskis
UMN signs signify lesions within the cerebral cortex or corticospinal tract (CST)
Describe lower motor neuron symptoms
Flaccidity
decreased reflexes
faciculations or muscle cramps
Conditions that have only peripheral effects at the NMJ and muscle have preserved reflexes
Discuss a broad approach to generalised weakness
In the generally weak patient rule out non neurological causes first – check circulating volume and composition
Check cardiac fucntion, red cellfucntion, systemic vasuclar tone and oxygenation.
If substrate delivery and plasma composition appear sufficient consider disturbance of cellular metbaolic machinery secondary to an endocrinopathy, toxin or mitochondrial dysfunction.
List a differential for combination of arm hand or leg weakness with ipsilateral facial involvement
This presentation is generally caused by a lesion in the contralateral cerebral cortex or the CST
Patient with equal loss of strength to the face hand and leg are more likely to have subcortical lesions disrupting all of these lesions as they funnel close together in the internal capsule
Sudden onset of weakness pattern implies haemorrhage or mass lesion
Gradual onset may be seen in demylination (e.g MS, acute demyelinating encephalomyelitis) or neoplasm (metastasis, astrocytoma, oligodendroglioma, ependymoma)
Discuss a differential for a combination of arm, hand or leg weakness with contralateral facial invovlement
This pattern indicates a brainstem lesion. – do a cranial nerve exam to identify the level of the lesion
Depressed concious state can be present if the brainstem reticular activating system is involved.
The two main broad resions for this presentation are vertebrobasilar insufficiency and demyelinating disease.
Discuss broad differential for limb weakness without facial involvement
A lesions in the medial contralateral cerebral homunculus (over the area where the lower extremity is represented)
A discrete internal capsule or brainstem lesion involving only the CST rather the the coticobulbar tracts
Brown sequard internal capsulr or brains stem lesion
Discuss brown sequard lesions
Caused by hemisection of the spinal cord involving all three major spinal tracts
1: corticospinal tract - causing ipsilateral flacid paralysis - from the level of the lesion
2: lesions of one or both DCML
- -lesions to fasciculus gracilis or fasciculus cuneatus result in ipsilateral proprioception loss as well as loss of all fine touch sensation
3: loss of the spinothalmic causes loss of contralateral temperature and pain sensation beginning one or two levels below that of the lesion
Causes:
- Trauma
- Demylination
- Ischaemia
- TB
Discuss differential for weakness in only one limb
Isolated weakness of one extremity is usually caused by a spinal cord or peripheral nerve lesion
Can include
- connective tissue disorder
- external compression (entrapment syndrome, compressive plexopathy)
- endocinopathy
- paraneoplastic syndrome
- toxins
- trauma
- vitamin D
Emergent
- iscahemai or compression of spinal cord
- acute demylination such as guillaine barre
- NMJ dysfunction – myasthenia or cholinergic crisis, botulism
Discuss differentials for weakness confined to lower extremities
Often will be accompanied by loss of pain and temperature as the spinothamlic tract runs close to the CST
DDX include
- Cauda equina
- anterior cord syndrome
- GBS
Discuss anterior cord syndrome
Caused by interruption of blood supply via the anterior spinal artery affected the CST and spinothalmic tract
Characterised by
- complete motor paralysis below the level of the lesion
- loss of pain and temperature
- preservation of proprioception and touch
- autnomic dysfunction with variation in BP and bowel and bladder dysfunction
- Flaccid internal and external anal sphincter, bladder retention
The most common cause is insufficienies in the aorta ie, dissection or AAA
Briefly discuss cauda equina syndrome
Caused by damage to the cauda equina the bundle of nerves which continues from the spinal cord - L4-5 - lower motor lesion
Incomplete
-loss of urgency or decreased sensation wihtout incontinence or retention
Comeplte
-urinary and or bowel retention or incontience
Signs and symtpoms incldue
- back pain
- saddle anaethesia
- Bladder and bowel dysfunction, decreased tone in urinary and anal sphincters, weakness of detruser leading to retention and post void residual incontinence
- sciatica
- sexual dysfucntion
- absent anal reflex
Causes 1) degenerative -lumbar disc herniation most common at L4/5 and L5/s1 -Lumbar spinal canal stenosis 2) infalammatory -ank spond 3) trauma -fracture dislocation 4) infection -arachnoiditis -epidural abscess 5) tumor -pirmary mets 6) vascular -aortic dissection -AVN
Discuss differential for weakness isolated to the upper limbs
This central cord pattern loaclizes to the central portion of the cervical spinal cord where CST fibers for hand and arm strength are located.
