Synopsis
Recognise major inherited dystrophy patterns, use genomic confirmation rather than phenotype alone, and anticipate respiratory, cardiac, swallowing, endocrine, anaesthetic and family risks across the life course.
- Muscular dystrophies are genetically diverse disorders causing progressive muscle degeneration; age at onset, distribution, contractures, cardiac involvement and inheritance guide the initial differential.
- Duchenne muscular dystrophy usually presents in early childhood with delayed motor milestones, calf pseudohypertrophy, Gowers manoeuvre and very high creatine kinase due to absent dystrophin.
- Becker dystrophy results from partially functional dystrophin and is often milder or later, but cardiomyopathy can be disproportionate to skeletal weakness.
- Facioscapulohumeral dystrophy produces facial weakness, scapular winging and humeral involvement, often asymmetrically, with hearing and retinal surveillance needed in selected patients.
- Limb-girdle muscular dystrophies are genetically heterogeneous and may preferentially involve pelvic or shoulder girdles with variable cardiac and respiratory risk.
- Myotonic dystrophy type 1 causes delayed muscle relaxation, distal and facial weakness, early cataract, conduction disease, sleepiness, respiratory failure, gastrointestinal dysmotility and endocrine features.
- Percussion or grip myotonia is best demonstrated by asking the patient to release a sustained hand grip or tapping thenar muscle, while cold can accentuate delayed relaxation.
- Creatine kinase may be strikingly raised in dystrophinopathy but only mildly abnormal in myotonic or facioscapulohumeral disease; a normal result does not exclude inherited muscle disease.
- Genetic testing should confirm the diagnosis and guide family counselling before muscle biopsy whenever a recognised molecular pathway is available.
- Management is anticipatory: corticosteroid and mutation-specific treatment for selected dystrophinopathy, cardiac and ventilatory surveillance, stretching, bone health, vaccination, rehabilitation and planned transition to adult services.
Key red flags
Syncope, palpitations, orthopnoea, recurrent chest infection, morning headache or daytime somnolence can signal conduction disease or nocturnal hypoventilation.
Investigation priorities
Detect muscle membrane injury and common mimics.
Management branches
Progressive muscle weakness, myotonia or a suggestive family history is identified.
- Map facial, scapular, axial, proximal and distal weakness, contractures, calf size and myotonia while checking sensation, reflexes, cardiac and respiratory symptoms.
- Construct a three-generation pedigree and obtain CK, ECG and targeted systemic tests, referring to a neuromuscular and clinical genetics service.
- Use the phenotype-directed NHS genomic test, explaining uncertain variants and avoiding irreversible predictive testing in relatives without genetic counselling.
Key medicines
Prednisolone or deflazacort in Duchenne dystrophyA paediatric neuromuscular specialist chooses the current daily or intermittent weight-based regimen, titrating for function, growth and adverse effects.Monitor growth, weight, blood pressure, glucose, cataract, behaviour, infection, adrenal suppression, puberty and bone; never stop long-term corticosteroid abruptly.
MexiletineFor disabling myotonia, specialists select a divided oral dose after baseline cardiac assessment and titrate according to the current BNF and local protocol.Review structural heart disease, conduction intervals, arrhythmia, liver function, interactions and gastrointestinal adverse effects; it does not treat progressive weakness.