Weakness | The Massachusetts General Hospital Handbook of Neurology

Authors: Flaherty, Alice W.; Rost, Natalia S.

Title: Massachusetts General Hospital Handbook of Neurology, The, 2nd Edition

> Table of Contents > Adult Neurology > Weakness

Weakness

A. See also

Neuromuscular Disorders, p. 80.

B. Terminology

Paresis is partial; plegia or paralysis is complete.

C. H&P

Numbness, pain, distal vs. proximal, bowel and bladder function, injuries, diurnal or exercise-induced fluctuation, tone, reflexes, atrophy, fasciculations, etc.

Figure 14. Muscle strength grading.

D. Upper motor neuron (UMN) vs. lower motor neuron (LMN) weakness

Both may be flaccid initially, but UMN lesion (corticospinal, pyramidal) usually develops spasticity and hyperreflexia; reflexes should be depressed in LMN lesion. May see fasciculations in LMN lesion; EMG will show fibrillations only after a few weeks. Dexterity is preferentially affected by upper motor neuron corticospinal lesion.

1. Spasticity: An exaggeration of stretch reflexes, causing velocity-dependent, clasp-knife rigidity, flexion dystonia, and flexor spasms, hyperreflexia.
- a. DDx: Extrapyramidal rigidity, muscle spasms,
- b. Rx: Muscle relaxants, see p. 173. Physical therapy. Orthopedic procedures to release contractions.

E. Bulbar vs. pseudobulbar palsy

1. Bulbar palsy: Lower motor neuron flaccid lesion of lower cranial nerves. Decreased gag.
2. Pseudobulbar palsy: Spastic, upper motor neuron lesion. Hyperactive gag. Causes include ALS, MS, and bilateral cerebral strokes. In the latter two, there is often pseudobulbar affect : excessive, inappropriate laughing and crying.

F. Hemiparesis

Ipsilateral arm and leg. Typically from corticospinal damage. Look for other signs (e.g., neglect, cranial nerve abnormalities) to localize further.

G. Monoparesis

Single limb. May have peripheral or central cause.

H. Paraparesis

Both legs. Usually spinal cord; look for sensory level. But consider falx meningioma or bilateral ACA infarcts.

I. Proximal, distal, or generalized weakness

1. Severe or quickly progressive quadriparesis: Consider high cervical or brainstem lesion, Guillain-Barr syndrome, botulism.

P.130

2. Slowly progressive: Consider neuropathies, neuromuscular dz.
3. Fluctuating weakness: Consider myasthenic syndromes, TIAs, hyper- or hypokalemic periodic paralysis.
4. Generalized weakness in the ICU: Mnemonic for DDx is MUSCLES: Medication, Undiagnosed neuromuscular disorder, Spinal cord damage, Critical illness polyneuropathy, Loss of muscle mass, Electrolyte disorders, Systemic illness.