AIM Step 10
3rd Year MBBS
MSK Module
3rd Year MBBS
MSK Module
Student Memory Support
Skeletal-Muscle Atrophy, Myopathies and Muscular Dystrophies
High-yield flashcards, mnemonics, comparisons and clinical hooks for rapid KMU revision.
1. High-Yield Flashcards
Tap each question to reveal the answer.
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What is skeletal-muscle atrophy?
A reduction in the size of individual muscle fibres, producing decreased muscle bulk and strength.
Which microscopic pattern suggests neurogenic atrophy?
Groups of small angular fibres, sometimes with fibre-type grouping after reinnervation.
Which changes suggest a primary myopathic process?
Scattered fibre-size variation, rounded fibres, necrosis, regeneration, internal nuclei and fibre splitting.
What is the hallmark morphology of dermatomyositis?
Perifascicular atrophy with perivascular and perimysial inflammation.
What is the key pathological feature of polymyositis?
Endomysial cytotoxic T lymphocytes directly surrounding and invading muscle fibres.
Which biopsy finding points toward inclusion-body myositis?
Rimmed vacuoles with abnormal protein inclusions and endomysial inflammation.
Which muscles are characteristically affected in inclusion-body myositis?
Quadriceps and finger-flexor muscles, often asymmetrically.
What serious complication may follow extensive toxic muscle injury?
Rhabdomyolysis with myoglobin release and acute kidney injury.
Which protein is absent in Duchenne muscular dystrophy?
Dystrophin.
How does dystrophin deficiency damage muscle fibres?
It makes the sarcolemma mechanically unstable, causing contraction-related injury, calcium entry and fibre necrosis.
What causes calf pseudohypertrophy in Duchenne muscular dystrophy?
Replacement of lost muscle fibres by fat and connective tissue.
Which investigation is markedly elevated in Duchenne muscular dystrophy?
Serum creatine kinase.
Which test confirms the cause of many hereditary myopathies?
Genetic testing.
What is an impairment?
Loss or abnormality of a body structure or function, such as paralysis of a limb.
What is the difference between DALY and QALY?
DALY measures health loss; QALY measures survival adjusted for quality of health.
What is the main preventive measure against poliomyelitis?
High poliovirus vaccination coverage supported by surveillance and rapid response.
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2. Mnemonics
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Mnemonic Title: Myopathic Biopsy Changes
V-N-R-F
Meaning: Variation in fibre size, Necrosis, Regeneration and Fibrosis.
Mnemonic Title: Duchenne Clinical Pattern
G-C-W
Meaning: Gowers sign, Calf pseudohypertrophy and Waddling gait.
Mnemonic Title: Poliomyelitis Control
V-S-R
Meaning: Vaccination, Surveillance and Rapid response.
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3. Memory Tables
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Neurogenic versus Myopathic Change
| Feature | Neurogenic | Myopathic |
|---|---|---|
| Primary lesion | Motor neuron or nerve | Muscle fibre |
| Fibre shape | Small and angular | Rounded and variable |
| Distribution | Grouped | Scattered |
| Special clue | Fibre-type grouping | Necrosis and regeneration |
Inflammatory Myopathies
| Feature | Dermatomyositis | Polymyositis | Inclusion-Body Myositis |
|---|---|---|---|
| Skin rash | Present | Absent | Absent |
| Inflammation | Perivascular and perimysial | Endomysial | Endomysial |
| Hallmark | Perifascicular atrophy | T-cell fibre invasion | Rimmed vacuoles |
| Weakness | Symmetrical proximal | Symmetrical proximal | Asymmetrical proximal and distal |
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4. Rapid Revision Points — Last-Minute Revision
- Disuse atrophy results from reduced protein synthesis and increased protein breakdown.
- Grouped angular fibres indicate denervation.
- Perifascicular atrophy is linked to dermatomyositis.
- Endomysial cytotoxic T cells are typical of polymyositis.
- Rimmed vacuoles suggest inclusion-body myositis.
- Glucocorticoid myopathy causes painless proximal weakness with little inflammation.
- Muscular dystrophy progresses from repeated necrosis to fibrosis and fatty replacement.
- Duchenne muscular dystrophy is X-linked recessive.
- Gowers sign reflects pelvic-girdle weakness.
- Proximal weakness with preserved sensation supports myopathy.
- DALYs rise as health loss increases; QALYs rise as healthy life improves.
- Poliomyelitis control requires vaccination, surveillance and rapid public-health response.
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KMU Trap: Calf enlargement in Duchenne muscular dystrophy is pseudohypertrophy caused by fat and fibrosis, not increased functional muscle.
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5. Clinical Memory Hooks
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Difficulty climbing stairs with heliotrope rash
→
dermatomyositis with perifascicular atrophy
→
dermatomyositis with perifascicular atrophy
Older patient with finger-flexor and quadriceps weakness
→
inclusion-body myositis
→
inclusion-body myositis
Drug exposure with muscle pain and dark urine
→
toxic myopathy with rhabdomyolysis
→
toxic myopathy with rhabdomyolysis
Boy with waddling gait, Gowers sign and large calves
→
Duchenne muscular dystrophy
→
Duchenne muscular dystrophy
Sudden flaccid weakness in a child
→
investigate through acute flaccid paralysis surveillance
→
investigate through acute flaccid paralysis surveillance
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6. Starred High-Yield Exam Points
- ⭐ Perifascicular atrophy is the hallmark of dermatomyositis.
- ⭐ Rimmed vacuoles with finger-flexor weakness indicate inclusion-body myositis.
- ⭐ Dystrophin loss causes sarcolemmal instability in Duchenne muscular dystrophy.
- ⭐ Markedly elevated creatine kinase supports Duchenne muscular dystrophy.
- ⭐ Genetic testing confirms many hereditary myopathies.
- ⭐ Myoglobin release in rhabdomyolysis may cause acute kidney injury.
- ⭐ Vaccination plus acute flaccid paralysis surveillance is central to poliomyelitis control.