## Distinguishing MG from LEMS: Clinical Features **Key Point:** Ocular and bulbar muscle involvement is the hallmark early feature that distinguishes MG from LEMS. In MG, ptosis and diplopia are often the presenting symptoms, whereas LEMS typically begins with proximal lower limb weakness. ### Clinical Comparison Table | Feature | Myasthenia Gravis | Lambert-Eaton Myasthenic Syndrome | |---------|-------------------|------------------------------------| | **Early involvement** | Ocular/bulbar muscles (70% of cases) | Proximal lower limbs | | **Ocular symptoms** | Present in 90% at onset | Rare (< 10%) | | **Autonomic signs** | Absent or minimal | Prominent (dry mouth, impotence, constipation) | | **Fatigue pattern** | Worsens with use, improves with rest | Improves with repeated use (post-tetanic potentiation) | | **Antibodies** | Anti-AChR (80%), anti-MuSK (20%) | Anti-VGCC (85%) | | **Associated malignancy** | Rare (10-15%) | Common (50-60%, SCLC) | **Clinical Pearl:** The **ocular-first presentation** is so characteristic of MG that its absence should prompt consideration of alternative diagnoses. LEMS patients rarely complain of diplopia or ptosis unless the disease is very advanced. **High-Yield:** In NEET PG, remember: **MG = Eyes first; LEMS = Legs first.** ### Why Other Options Are Misleading - **Worsening with repetitive use:** Both conditions show this pattern (though LEMS improves paradoxically with sustained contraction due to post-tetanic potentiation). - **Improvement with rest:** Both MG and LEMS show symptom fluctuation; this is not discriminatory. - **Autonomic dysfunction:** While prominent in LEMS, it is not a feature of MG—but this is a secondary discriminator, not the primary one. **Mnemonic:** **LEMS = Legs, Autonomy, Malignancy, SCLC** (proximal weakness, autonomic symptoms, cancer association).
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