369 Ch 368. Weakness and Paralysis

Weakness = loss of muscle strength；must distinguish true weakness from fatigue, asthenia, deconditioning；localize along motor pathway: (1) UMN — cortex/internal capsule/brainstem/spinal cord (spasticity + hyperreflexia + Babinski + minimal atrophy); (2) LMN — anterior horn cell + nerve root + plexus + peripheral nerve (flaccid + hyporeflexia + atrophy + fasciculations); (3) NMJ — myasthenia gravis (fatigable + ocular/bulbar), LEMS (proximal, improves with use); (4) Muscle — myopathy (proximal symmetric + ↑ CK)；distribution clues: hemi (brain), para (spinal cord T6 above involves arms), quadriplegic (high cervical), distal symmetric (peripheral neuropathy), proximal symmetric (myopathy), bulbar (NMJ, MN, brainstem)；time course: sudden (stroke, GBS, spinal cord), days-weeks (GBS, MG, polymyositis), months-years (degenerative ALS, MD, MS)；workup: EMG/NCS + CK + imaging based on localization + antibodies (MG, autoimmune)。