Chapter 13 - Weakness

Question 1

What is weakness?

Answer 1

Objective (true weakness- loss of strength from a neurologic or muscular disease process) vs. other mimickers

Question 2

what is UMN lesion and what are the signs?

Answer 2

UMN lesion: lesion in the cerebral cortex or corticospinal tract of the brainstem and spinal cord

SSx: (1 or more present: positive for central nervous system etiology)
1) spasticity to extension in upper extremities/ flexion of lower extremities
2) hyper-reflexia
3)pronator drift
4)hoffmann’s/tinel’s sign and babinski’s sign (up going toes)
normal muscle bulk

a number of strokes have clonus on exam

Question 3

What is LMN lesion and what are the signs?

Answer 3

Lesion in the anterior horn, nerve root, axon or peripheral nerve

SSx:

1) flaccidity
2) hyporeflexia
3) fasciculation
4) loss of muscle bulk

Question 4

NMJ lesion signs?

Answer 4

disrupt normal signalling from the pre-synaptic motor neuron to the post-synaptic muscle fiber

SSx:

1) slowly progressive or fluctuating signs
2) bulbar or ocular signs
3) mixed UMN and LMN pattern
4) bilateral proximal muscle weakness
5) loss of muscle bulk

Question 5

10 neuromuscular causes of weakness and describe their basic pathophysiologic mechanism

Answer 5

A) Critical diagnosis

1) cerebral cortex or subcortical” ischemic or hemorrhagic stroke (CVA)
2) brainstem ischemic or hemorrhagic stroke CVA
3) Spinal cord: ischemia, compression (disk, abscesses, hematoma)
4) peripheral nerve: acute demyelination GBS
5) NMJ: myasthenia gravis or cholinergic crisis, botulism, tick paralysis, organophosphate poisoning
6) Muscle: rhabdomyolysis

B) Emergent diagnosis

1) cerebral cortex or subcortical: tumor, abscess, demyelination
2) brainstem: demyelination
3) spinal cord: demyelination, compresion (disk, spondylosis
4) peripheral nerve: compressive plexopathy (hematoma, aneurysm)
5) Muscle: inflammatory myositis

Question 6

Warning signs of impending respiratory failure in patient with Neuromuscular weakness?

Answer 6

1) climbing pCO2
2) decreased LOC
3) decreasing peak flows - effort is weaning
4) tachypnea
5) respiratory distress with shallow respiration
6) accessory muscle recruitment

Question 7

7 non-emergent causes of peripheral neuropathy

Answer 7

1) connective tissue disorder
2) external compression (
3) endocrinopathy (diabetes)
4) paraneoplastic syndromes
5) toxins (alcohol)
6) trauma
7) vitamin D deficiency

Question 8

Causes of generalized weakness, non-neuromuscular

Answer 8

1) alterations in plasma volume (dehydration)
2) alterations in plasma composition (glucose, electrolytes)
3) derangement in circulating RBC (anemia, polycythemia)
4) decrement in cardiac function pump (MI)
5) drop in systemic vascular resistance: (vasodilatory shock)
6) increased metabolic demand (infection, endocrinopathy, toxin
7) mitochondrial dysfunction : (severe sepsis or toxin mediated)
8) global depression of CNS (sedatives, stimulant withdrawal

Question 9

Clinical pearls for the weak patient:

Answer 9

1) tachypnea and shallow resp- signify impending respiratory failure - prepare for PPV
2) sudden onset of focal weakness is vascualr cause until proven otherweise (occlusion vs. Hemorrhage vs. Ischemic )
3) presence of severe headache with unilateral weakness or midline back pain with lower extremity weakness is a compressive space occupying lesion until proven otherwise
4) patients with UMN signs that have weakness that localizes to spinal cord - considered emergent
5) presence of anorectal or bladder insufficiency without other explanation suggests UMN lesion or cauda equina synrome
6) lab tests are useful for excluding non-neuromuscular causes of weakness, with two exceptions: a CK in inflammatory myositis, a potassium level in channelopathies