👶 Floppy Infant – Key Distinctions
• Cerebral hypotonia: alert, poor suck, seizures, brisk reflexes, dysmorphic features
• Peripheral hypotonia: weak cry, poor suck, frog-leg posture, absent reflexes, weakness
• Central (brain) vs Peripheral (nerve, NMJ, muscle)
🦴 Spinal Muscular Atrophy (SMA)
• Degenerative loss of anterior horn cells
• Type I (Werdnig-Hoffmann): onset <6 months, severe hypotonia, areflexia, tongue fasciculations, never sits
• Type II: onset 6-18 months, sits but never walks
• Genetic testing (SMN1 deletion) diagnostic
💪 Muscular Dystrophy
• Duchenne (X-linked, dystrophin deficiency): onset 2-5 years, calf pseudohypertrophy, Gower sign, elevated CK, genetic testing
• Becker (later onset, milder)
• Myotonic dystrophy: myotonia, facial weakness, congenital form severe hypotonia at birth
⚠️ Acute Weakness (Urgent)
• Guillain-Barré syndrome: ascending paralysis, areflexia, elevated CSF protein without pleocytosis, post-infectious
• Infantile botulism: descending paralysis, constipation, ptosis, poor suck (honey exposure), treat with antitoxin
• Myasthenia gravis: fatigable weakness, ptosis, diplopia, improve with rest, Tensilon test
📌 Decision strategy: Central vs peripheral hypotonia based on reflexes, alertness, and signs. CK extremely elevated → Duchenne. Normal CK → consider SMA, myopathy. Acute ascending weakness → GBS. Descending + constipation + poor suck → botulism.