Neuromuscular: Muscle Disorders
A 30-slide clinical learning module · Dystrophinopathies, congenital myopathies, and Pompe disease
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Module Outline
🩺 Part 1
💪 Part 2
🔬 Part 3
🧬 Part 4
📋 Part 5
Slide 1/30
🩺 Part 1: Approach to Muscle Disease
The First 30 Seconds: Is This a Muscle Problem?
Pattern recognition before the workup
- 1Muscle weakness is a localization problem before it's a genetic problem. Every weak child should first be placed on the motor unit: brain/spinal cord (central), anterior horn (SMA), nerve (CMT), NMJ (CMS, myasthenia), or muscle (dystrophinopathy, congenital myopathy, metabolic myopathy).
- 2Clues that the problem is at the MUSCLE level: proximal-greater-than-distal weakness, intact reflexes early (lost late), no sensory findings, elevated CK, Gower's sign, calf pseudohypertrophy in dystrophinopathy.
- 3Clues AGAINST a primary muscle process: areflexia out of proportion to weakness (think nerve or anterior horn), sensory loss (nerve), fluctuating weakness or fatigability (NMJ), tongue fasciculations (anterior horn / SMA type 1).
- 4Action: every child with persistent weakness deserves a CK level. CK > 10× upper limit → strongly muscle-localizing (dystrophinopathy until proven otherwise). CK 2–10× → dystrophinopathy, LGMD, congenital myopathy. CK normal → does not rule out a myopathy (congenital myopathies, Pompe LOPD, channelopathies can all have normal CK).
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Clinical Pearl
Always check a CK before ordering a muscle biopsy. If CK is > 10× upper limit in a boy with proximal weakness, order DMD gene testing FIRST — del/dup analysis catches ~65–70% of pathogenic DMD variants and avoids an unnecessary biopsy in most cases.
DMD/BMD lecture deck (DCB); Birnkrant et al., Lancet Neurol 2018