Clinical Neuromuscular Disease: Localization and Pattern Recognition
Localize first, then name the disease
Every neuromuscular question becomes easier if you place the lesion before recalling a diagnosis. Upper motor neuron signs (spasticity, hyperreflexia, Babinski) point to brain or spinal cord; lower motor neuron signs (atrophy, fasciculations, areflexia) point to anterior horn, root, plexus, or peripheral nerve. Sensory loss and pain usually mean root, plexus, or nerve; sensory sparing with weakness suggests motor neuron disease, neuromuscular junction (NMJ), or muscle. NMJ disorders cause fatigable weakness with normal sensation and reflexes, though reflexes may be depressed in Lambert-Eaton. Myopathies cause proximal weakness, normal sensation, and often normal or mildly elevated CK.
Know the classic patterns. ALS: painless progressive weakness, fasciculations, mixed UMN/LMN signs, normal sensory NCS. Guillain-Barre: ascending symmetric weakness, areflexia, albuminocytologic dissociation, early NCS may be normal. CIDP: progressive or relapsing demyelinating NCS. Myasthenia gravis: ptosis, diplopia, bulbar weakness, variability, decrement on repetitive stimulation. Lambert-Eaton: proximal weakness, autonomic symptoms, incremental response. Inflammatory myopathy: proximal weakness, CK elevation, myopathic EMG.
Traps: attributing sensory symptoms to ALS; calling a normal NCS normal in early GBS; missing bulbar or respiratory involvement; confusing radiculopathy with plexopathy when multiple myotomes are involved; forgetting that myotonic dystrophy can present with distal weakness and myotonia.
Worked example: a 58-year-old has 8 months of painless progressive hand weakness, tongue fasciculations, hyperreflexia, and normal sensory NCS. The combination of LMN findings (atrophy and fasciculations) and UMN findings (hyperreflexia) with sensory sparing strongly suggests ALS; EMG confirms widespread active denervation.
Rule of thumb: 'Sensory loss plus areflexia equals peripheral nerve; sensory sparing plus hyperreflexia equals central; fatigability equals NMJ; proximal weakness with normal sensation equals muscle.'