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2 Patient who has Weakness Cheat Sheet (DRAFT) by

Distribution & 'types' of weakness

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Weakness overview

Distri­bution: reflects the site of lesion (e.g. proximal, distal, bilateral, unilat­eral, etc.)
Type: reflects the element of the nervous system that's impaired
To understand nature of pathology & aetiology of muscle weakness, what 4 things need to be considered?
1. Type of weakness
2. Distri­bution of weakness
3. Time course of onset
4. Mode of onset
Weakness vs. fatigue:
- Weakness: is regional
- Fatigue: is genera­lised
Pt records:
- Sense of clumsi­ness, tightness, instability
- Uncoor­dinated movement
- Numbness
Physical manife­sta­tions:
- Clumsiness
- Uncoor­dinated movement
- Loss of fine motor skills
- Imbalance
4 consid­era­tions of weakness:
- Type of weakness
- Distri­bution of weakness
- Time course of onset
- Mode of onset


Introd­uction: Causes of weakness are catego­rised by lesion location. Some disorders have charac­ter­istic of lesions in more than one location. E.g. Amyotr­ophic lateral sclerosis (ALS) may have findings of both UMN & LMN dysfun­ction. Disorders of the SC may affect tracts from UMN, LMN (anterior horn cells), or both
Common causes of focal weakness
- Stroke: unilateral weakness
- Neurop­athies: including trauma or entrapment caused (e.g. carpal tunnel syndrome) & that are immune­-me­diated (e.g. Bell palsy)
Temporary focal weakness:
- TIA (transient ischemic attack)
- Hypogl­yca­emia: with treatment hypogl­ycaemia & resulting weakness resolve
Genera­lised weakness:
- Disuse atrophy: resulting from illness or frailty (speci­fically in older pts)
- Genera­lised muscle wasting: due to prolonged immobi­lis­ation in an intensive care unit (ICU) - aka ICU myopathy
- Critical illness polyne­uro­pathy - aka ICU neuropathy
- Common myopat­hies: e.g. alcoholic myopathy, hypoka­laemia, cortic­ost­eroid myopathy
- Use of paralytic drugs in critical care pts


Introd­uction: Many pts report weakness when they have fatigue. This can prevent maximal effort & muscle perfor­mance during strength testing
Common causes:
- Acute severe illness of almost any cause, cancers, chronic infections (e.g.HIV, hepatitis, endoca­rditis, mononu­cle­osis), endocrine disorders, renal failure, hepatic failure, heart failure, & anaemia
- Multiple sclerosis can cause daily fatigue that increases with exposure to heat & humidity
- Pts with fibrom­yalgia, depression or chronic fatigue syndrome may report weakness or fatigue but have no defined objective abnorm­alities


Introd­uction: Voluntary movement initiated in cerebral cortex in the posterior aspect of the frontal lobe. Neurons involved - UMN or cortic­ospinal tract nuerons - synapse with LMN in the spinal cord. LMN transmit impulses to the neurom­uscular junction to initiate muscle contra­ction
Common mechanism of weakness include dysfun­ction of:
- UMN: cortic­ospinal & cortic­obulbar tract lesions
- LMN: due to peripheral poly neurop­athies or anterior horn cell lesions
- Neurom­uscular junction
- Muscle: due to myopathies
Location correlates with physical findings:
- UMNL: disinh­ibits LMN → causing ↑ muscle tone (spacticity) & ↑ muscle stretch reflexes (hyperr­eflexia); Babinski reflex is specific for cortic­ospinal tract dysfun­ction; UMNL can also ↓ tone & reflexes if motor paralysis is sudden & severe (e.g spinal cord transe­ctions → tone 1st ↓, then ↑ gradually over days/w­eeks) or if lesion damages the motor cortex of the precentral gyrus & not nearby motor associations
- LMNL: disrupts reflex arcs → causing hypore­felxia & ↑ muscle tone (flaccidity), & may cause fascic­ula­tions; with time, muscle atrophy
- Peripheral polyne­uro­pat­hies: most noticeable in the longest nerves (i.e. weakness is prominent in the distal limb than the proximal & in legs more than arms) & produce signs of LMNL (e.g. ↓ reflexes & muscle tone)
- Neurom­uscular junction - myasthenia gravis: (most common disorder) fluctu­ating weakness that worsens with activity & lessens with rest
- Diffuse muscle dysfun­ction: (myopa­thies) most noticeable in the largest muscle groups (proximal muscles)


Temporal pattern:
Anatomic pattern:
Physical examin­ation:
Additional findings:

Key points

Distin­guish loss of muscle strength from a feeling of fatigue
⏺ If fatigue has no anatomic or temporal pattern of weakness in pts with a normal physical examin­ation, suspect chronic fatigue syndrome, an as-yet undisc­overed systemic illness (e.g. severe anaemia, hypoth­yro­idism, Addison disease), a psycho­logic problem (e.g. depres­sion), or an adverse drug effect
⏺ If pts have true muscle weakness, first focus on determ­ining whether weakness is caused by dysfun­ction of the brain, spinal cord, plexuses, peripheral nerves, neurom­uscular junction, or muscles
⏺ If pts have hyperr­eflexia & increased muscle tone (spast­icity), partic­ularly if Babinski reflex is present, suspect an UMN (corti­cos­pinal tract) lesion in the brain or spinal: MRI is usually required
⏺ If pts have hypore­flexia, ↓ tone, atrophy, & fascic­ula­tions, suspect a LMNL
⏺ If pts have difficulty climbing stairs, combing hair, & standing up with predom­inantly proximal muscle weakness & intact sensation, suspect myopathy