369.1 🎓 醫孞生版

369.1.0.1 📌 䞀頁重點

369.1.0.1.1 Localization Framework

369.1.1 Motor Pathway

Brain (UMN) → corticospinal tract → spinal cord → anterior horn cell (LMN) → nerve root → plexus → peripheral nerve → NMJ → muscle

Damage at each level produces characteristic pattern.

369.1.1.0.1 UMN vs LMN

369.1.2 UMN (Upper Motor Neuron)

  • Location: cortex → internal capsule → brainstem → corticospinal tract → spinal cord
  • Spastic tone (velocity-dependent)
  • Hyperreflexia, clonus
  • Babinski sign (extensor plantar)
  • Minimal atrophy (use-related)
  • No fasciculations
  • Pattern: distal hand extensors weaker; arm flexors stronger; leg flexors weaker; leg extensors stronger (“pyramidal pattern”)

369.1.3 LMN (Lower Motor Neuron)

  • Location: anterior horn cell → root → plexus → nerve → NMJ → muscle (for the lower motor neuron unit)
  • Flaccid tone
  • Hyporeflexia/areflexia
  • Atrophy (denervation)
  • Fasciculations (anterior horn cell)
  • Plantar downgoing

369.1.4 Mixed UMN + LMN

  • ALS (anterior horn cell + corticospinal tract)
  • Cervical spondylosis (UMN below, LMN at level)
  • Subacute combined degeneration (B12)
  • HTLV-1 myelopathy
369.1.4.0.1 Localization by Distribution

369.1.5 Hemiparesis

  • Cortical or subcortical stroke (most common)
  • Internal capsule lacune
  • Brainstem (with crossed signs)
  • Spinal cord (Brown-Séquard)

369.1.6 Paraparesis (Both Legs)

  • Spinal cord (thoracic + lumbar level)
  • Cauda equina
  • Bilateral parasagittal lesion
  • Bilateral ACA

369.1.7 Quadriparesis

  • High cervical spinal cord (above C5)
  • Brainstem
  • Diffuse CNS

369.1.8 Distal Symmetric

  • Peripheral neuropathy (most common — diabetic, etc.)
  • Length-dependent (feet first)

369.1.9 Proximal Symmetric

  • Myopathy (polymyositis, dermatomyositis, IBM)
  • Some peripheral neuropathies (CIDP, AIDP)
  • NMJ (MG, LEMS)

369.1.10 Asymmetric/Multifocal

  • Mononeuritis multiplex (vasculitis, diabetes, HIV, leprosy)
  • Multifocal motor neuropathy
  • Polyradiculopathy

369.1.11 Cranial / Bulbar

  • NMJ (MG)
  • Brainstem stroke
  • MND (especially bulbar-onset ALS)
  • Cranial neuropathies
369.1.11.0.1 Common Causes by Pattern

369.1.12 Sudden Onset

  • Stroke (ischemic or hemorrhagic)
  • Spinal cord trauma or infarct
  • Acute paralytic poliomyelitis
  • Hypokalemic periodic paralysis
  • Transverse myelitis

369.1.13 Hours-Days

  • Guillain-Barré (ascending, areflexia, often after URI/GI)
  • Tick paralysis
  • Botulism
  • Diphtheria
  • Periodic paralysis

369.1.14 Days-Weeks

  • Myasthenia gravis (fluctuating, fatigable)
  • Polymyositis, dermatomyositis
  • CIDP
  • Vasculitic neuropathy
  • Hypothyroid myopathy
  • Drug-induced (steroid, statin)

369.1.15 Months-Years

  • ALS (motor neuron disease)
  • Muscular dystrophies
  • MS (relapsing or progressive)
  • Hereditary neuropathies (CMT)
  • Spinal cord compression (tumor, spondylosis)
  • Cervical spondylotic myelopathy
369.1.15.0.1 Workup

369.1.16 History

  • Time course
  • Distribution
  • Associated symptoms (pain, sensory, autonomic, cranial)
  • Triggers (exertion, fasting, K+ changes)
  • Family history
  • Medications
  • Exposures
  • Comorbidities (DM, autoimmune, cancer)

369.1.17 Exam

  • MRC 0-5 strength
  • Tone
  • Reflexes + plantars
  • Sensation
  • Cranial nerves
  • Bulk + fasciculations
  • Gait
  • Cerebellar
  • Specific tests (Hoffmann, Lhermitte, Spurling, fatigability)

369.1.18 Labs

  • CK (elevated in myopathy, rhabdo)
  • Electrolytes (K+, Na+, Mg2+, PO4-)
  • TSH (thyroid myopathy)
  • B12, folate
  • HIV, syphilis
  • Heavy metals (lead, arsenic)
  • Autoimmune (ANA, anti-Jo-1, anti-AChR, anti-MuSK, anti-VGCC)
  • Paraneoplastic panel

369.1.19 Electrophysiology

  • EMG/NCS (key for localization)
  • Distinguishes neuropathy vs NMJ vs myopathy
  • Axonal vs demyelinating
  • RNS for MG (decremental) + LEMS (incremental)

369.1.20 Imaging

  • MRI brain (UMN, central cause)
  • MRI spinal cord (myelopathy)
  • Plexus MRI (plexopathy)
  • Muscle MRI (myopathy)
  • CT chest (thymoma in MG)

369.1.21 Other

  • Muscle biopsy (myopathy)
  • Nerve biopsy (selected)
  • Genetic testing
  • LP/CSF (GBS, CIDP, MS, autoimmune encephalitis)

369.1.21.1 🩺 床邊速查

  • Localize first along motor pathway
  • UMN: spastic + hyperreflexia + Babinski + minimal atrophy
  • LMN: flaccid + hyporeflexia + atrophy + fasciculations
  • NMJ: fatigable (MG), proximal improves with use (LEMS)
  • Myopathy: proximal symmetric, ↑ CK
  • Distribution clues: hemi (brain), para (spinal), distal symmetric (PN), proximal symmetric (myopathy)
  • Time course: sudden (vascular), days (GBS), weeks (MG), months-years (ALS, MD)
  • EMG/NCS key for localization