Duchenne Muscular Dystrophy
Neurology
Illness script · Neurology
Duchenne Muscular Dystrophy
X-linked recessive progressive myopathy caused by dystrophin deficiency, leading to irreversible skeletal and cardiac muscle degeneration in young males.
This illness script for Duchenne Muscular Dystrophy covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- X-linked recessive: affects males almost exclusively
- Onset typically age 2–5 years
- 1 in 3,500 male births; ~1/3 are de novo mutations
- Positive family history on maternal side
- Becker MD is allelic but milder (partial dystrophin function)
02
Presentation
- Proximal muscle weakness first: difficulty climbing stairs, rising from floor
- Gowers' sign: uses hands to 'walk up' thighs to stand from floor (pathognomonic)
- Pseudohypertrophy of calves (fibrofatty replacement, not true muscle hypertrophy)
- Waddling gait and toe-walking by school age
- Wheelchair-bound by age 10–12
- Dilated cardiomyopathy and respiratory failure in late teens/early 20s
03
Pathophysiology
- Frameshift mutations in DMD gene (Xp21) → absent dystrophin protein
- Dystrophin normally links cytoskeleton to extracellular matrix, protecting myocytes from contraction-induced injury
- Without dystrophin, repeated microtrauma → myocyte necrosis → fibrofatty replacement
- Dilated cardiomyopathy develops as cardiac muscle is similarly affected
04
Diagnostics
- CK markedly elevated (10–100× normal) — earliest lab abnormality
- Genetic testing (DMD gene mutation analysis) — gold standard, confirms diagnosis
- Muscle biopsy: absent dystrophin on immunostaining (if genetics inconclusive)
- EMG shows myopathic pattern (low-amplitude, short-duration potentials)
- Echo/EKG annually for cardiomyopathy monitoring
05
Management
- Corticosteroids (prednisone or deflazacort): slow progression, prolong ambulation — mainstay
- Exon-skipping therapies (e.g., eteplirsen for exon 51 skip) for eligible mutations
- ACE inhibitors/beta-blockers for dilated cardiomyopathy
- Non-invasive ventilation (BiPAP) for respiratory failure
- Multidisciplinary care: PT, OT, pulmonology, cardiology; genetic counseling for family
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Becker Muscular Dystrophy
Becker has partial dystrophin (in-frame mutation), so onset is later (teens) and ambulation preserved past age 15.
Limb-Girdle Muscular Dystrophy
Limb-girdle is autosomal and lacks Gowers' sign prominence; dystrophin is normal on biopsy.
Spinal Muscular Atrophy (SMA)
SMA is a lower motor neuron disease (SMN gene); CK is normal/low and fasciculations are present — absent in DMD.
Myasthenia Gravis
MG causes fatigable weakness with ocular/bulbar involvement and normal CK; EMG shows decremental response on repetitive stimulation.
Keep reading
Full library- Dilated CardiomyopathyVentricular dilation with systolic dysfunction (reduced EF) causing heart failure, often idiopathic or from identifiable insult.
- Ectopic PregnancyImplantation of a fertilized ovum outside the uterine cavity, most commonly in the fallopian tube (~95%).
Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.