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This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
Key points
- First decide whether the complaint is true weakness, fatigue, pain-limited movement or functional limitation.
- Localise: UMN, LMN, peripheral nerve, neuromuscular junction or muscle.
- Rapidly progressive weakness, bulbar symptoms or dyspnoea are emergencies because respiratory failure may develop.
- GBS is ascending weakness with areflexia; myasthenia is fatigable ocular/bulbar/proximal weakness; myopathy is proximal weakness with raised CK.
- Initial tests include glucose/electrolytes, TSH, CK, medication review and targeted neurophysiology/imaging.
Approach to the Presentation
Generalized weakness is broad; the exam rewards anatomical localisation. Clarify time course, distribution, fatigability, sensory symptoms, pain, reflex changes, autonomic symptoms, bulbar symptoms and respiratory symptoms. Review medications carefully: statins, steroids, antipsychotics, sedatives and alcohol are common contributors. Examine power, tone, reflexes, sensation, cranial nerves, gait and respiratory function.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Guillain-Barré syndrome | must-not-miss | Progressive ascending weakness, areflexia, paraesthesias, autonomic instability after infection | NCS/EMG; CSF albuminocytologic dissociation after first week; monitor FVC/NIF |
| Myasthenia gravis crisis | must-not-miss | Fatigable ptosis/diplopia, bulbar weakness, proximal weakness, dyspnoea; worse with exertion | Bedside ice pack, AChR/MuSK antibodies, EMG; FVC for crisis |
| Spinal cord compression/myelopathy | must-not-miss | Weakness with sensory level, hyperreflexia, bowel/bladder dysfunction or back/neck pain | Urgent MRI spine |
| Hypokalaemic or metabolic paralysis | must-not-miss | Acute flaccid weakness, arrhythmia risk; diuretics, GI losses, thyrotoxicosis | Electrolytes, ECG |
| Medication/toxin myopathy | common | Statins, steroids, alcohol, colchicine; proximal weakness or myalgia | CK and medication withdrawal/rechallenge history |
| Peripheral neuropathy | common | Distal weakness/sensory loss, reduced reflexes; diabetes, B12, alcohol, renal disease | A1c, B12, SPEP, NCS/EMG |
| Endocrine weakness | common | Hypothyroid myopathy, hyperthyroid periodic paralysis, adrenal/electrolyte disorders | TSH, electrolytes, CK |
| Inflammatory myopathy | less common | Symmetric proximal weakness, difficulty rising/climbing stairs; possible rash or interstitial lung disease | CK, ESR/CRP, myositis antibodies, EMG/MRI, muscle biopsy |
| Motor neuron disease | less common | Progressive weakness with mixed UMN/LMN signs, fasciculations, no sensory loss | EMG and neurology assessment |
| Functional weakness | less common | Inconsistent weakness, Hoover sign, non-anatomical pattern; diagnose positively | Clinical exam after excluding urgent pathology |
Red Flags & Key History
Symptoms
Dyspnoea, orthopnoea, weak cough or bulbar symptoms
Rapid progression over hours-days
Bowel/bladder dysfunction or sensory level
Autonomic instability
Fatigability with ocular symptoms
Signs
FVC reduction or hypoxia/hypercapnia
Areflexia with ascending weakness
Hyperreflexia, clonus or Babinski
Ptosis/diplopia worsening with sustained gaze
Approach to Investigation
First-line
Bedside respiratory assessmentFVC/NIF if neuromuscular weakness suspected.
Glucose, electrolytes, calcium, magnesium, renal/liver functionIdentify reversible metabolic weakness.
CK and urinalysisMyopathy/rhabdomyolysis.
TSH, B12, CBC, ESR/CRPScreen common systemic causes.
Second-line
MRI brain/spineUMN signs, sensory level, bowel/bladder symptoms or central lesion concern.
NCS/EMGDifferentiate neuropathy, motor neuron disease, neuromuscular junction and myopathy.
AutoantibodiesAChR/MuSK for myasthenia; myositis antibodies where indicated.
Specialist
NeurologyRapid progression, respiratory/bulbar involvement, suspected GBS/MG/MND/myelopathy.
ICURespiratory compromise or autonomic instability.
Management Principles
MCC Weakness objective + Canadian neuromuscular practice patterns1
Stabilize first
- Assess airway, swallowing and respiratory mechanics
- Admit rapidly progressive weakness for monitoring
2
Treat emergencies
- GBS: IVIG or plasma exchange and DVT/respiratory monitoring
- Myasthenic crisis: ICU, ventilatory support, IVIG/plasma exchange; avoid worsening drugs
- Cord compression: urgent MRI, steroids if malignant compression suspected, neurosurgery/radiation oncology
3
Cause-specific outpatient care
- Correct electrolytes/endocrine disease
- Stop offending drugs
- Physiotherapy/OT, falls prevention and specialist follow-up
Complications & Pitfalls
- Calling it fatigue: document objective power and reflexes.
- Missing respiratory failure: oxygen saturation can be normal until late in neuromuscular weakness.
- Forgetting medications: statins, steroids and sedatives are common contributors.
- Not localising: UMN signs, reflex loss and sensory level direct the workup.
MCCQE1 Exam Tips
- 1GBS = ascending weakness plus areflexia; monitor FVC.
- 2Myasthenia = fatigable ocular/bulbar weakness; pupils remain normal.
- 3Cord lesion = weakness plus sensory level and bladder/bowel symptoms.
- 4Proximal weakness with high CK points to myopathy.
- 5True weakness means reduced power, not tiredness.
- 6Respiratory assessment is a next-best-step trap in neuromuscular disease.
Put your reading into practice
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