Limb weakness is a common but broad clinical presentation, arising from neurological, muscular, spinal, metabolic, or systemic causes. A systematic approach is vital: ⚡ onset (sudden vs gradual), ⏳ duration, pattern (proximal vs distal), and associated features (sensory loss, pain, systemic illness). Early recognition of emergencies such as stroke, spinal cord compression, or Guillain-Barré syndrome can be life-saving.

📝 History

Onset: ⚡ Sudden (stroke, spinal cord infarct), ⏳ gradual (MND, muscular dystrophy), 🌀 episodic (myasthenia gravis).
Duration: Acute vs chronic → important diagnostic clue.
Associated Symptoms:
- 🌡️ Fever, weight loss → infection, malignancy.
- 🔌 Sensory disturbance → neuropathy/spinal lesion.
- 🔥 Pain → radiculopathy, inflammatory myopathy.
Pattern: Proximal 🦵 weakness → myopathy/metabolic. Distal ✋ weakness → neuropathy/MND.
Precipitating Events: Recent infection (GBS), drugs (statins, steroids), toxins (alcohol, chemotherapy).
Family History: Neuromuscular disorders, muscular dystrophy, inherited neuropathies.

🩺 Examination

Strength: Grade using MRC scale 0–5.
Reflexes: ↑ = UMN lesion; ↓/absent = LMN lesion.
Muscle bulk & tone: Wasting, fasciculations (MND), spasticity (UMN).
Coordination: Ataxia, dysmetria → cerebellar involvement.
Gait:
- Foot drop 👣 → peroneal neuropathy/MS.
- Waddling gait 🐧 → proximal myopathy.
- Spastic gait 🧍‍♂️ → UMN lesion.

🧾 Common Causes

Neurological: Stroke, multiple sclerosis, MND, peripheral neuropathy, GBS.
Muscular: Muscular dystrophies, myositis, metabolic myopathies.
Spinal cord: Compression, trauma, transverse myelitis.
Autoimmune: Myasthenia gravis, SLE, dermatomyositis.
Metabolic/Endocrine: Hypokalaemia, thyroid disorders, diabetes, Cushing’s.
Toxins/Drugs: Alcohol, statins, steroids, chemotherapy (vincristine).

🔎 Investigations

Bloods: CBC, U&E, CK, thyroid function, autoimmune screen, glucose, B12.
Neuroimaging: CT/MRI brain/spine for stroke, compression, demyelination.
Electrophysiology: Nerve conduction studies, EMG.
CSF: Oligoclonal bands (MS), albuminocytologic dissociation (GBS).
Muscle Biopsy: For myopathies and dystrophies.

📊 Causes of Limb Weakness

Cause	Description	Clinical Features	Key Tests	Management
Stroke (CVA) ⚡	Acute ischaemia or haemorrhage in the brain.	Sudden hemiparesis, facial droop, dysphasia, visual loss.	CT/MRI brain, carotid Doppler, ECG (AF).	Thrombolysis/thrombectomy, antiplatelets, BP control, rehab.
Multiple Sclerosis 🧩	Autoimmune demyelination of CNS.	Episodic weakness, optic neuritis, sensory loss, ataxia.	MRI brain/spine, CSF oligoclonal bands.	Immunomodulators, steroids for relapse, physio.
Guillain-Barré Syndrome 🌀	Acute post-infectious demyelinating polyneuropathy.	Ascending symmetrical weakness, areflexia, ± resp failure.	NCS/EMG, LP (↑ protein, normal cells).	IVIG or plasmapheresis, ITU if severe.
Myasthenia Gravis 🎯	Autoimmune blockade at neuromuscular junction.	Fluctuating weakness, ptosis, diplopia, bulbar symptoms.	AChR antibodies, EMG, CT chest (thymoma).	Pyridostigmine, immunosuppression, thymectomy.
Peripheral Neuropathy 🔌	Axonal or demyelinating damage, often diabetic.	Stocking–glove weakness, numbness, pain, areflexia.	NCS/EMG, B12, glucose, TFTs.	Control cause (e.g. diabetes), neuropathic pain meds, physio.
Amyotrophic Lateral Sclerosis (ALS) 🧠	Degenerative UMN + LMN disease.	Progressive weakness, fasciculations, dysarthria, no sensory loss.	EMG (denervation), MRI to exclude mimics.	Riluzole, supportive care, ventilatory support.
Spinal Cord Compression 🦴	Compression from tumour, abscess, disc, or trauma.	Weakness below lesion, sensory level, sphincter dysfunction.	MRI spine, CT if contraindicated.	Steroids, urgent neurosurgery/oncology.
Myopathies (e.g. polymyositis, dystrophy) 💪	Muscle fibre damage, autoimmune or inherited.	Proximal weakness, rash (dermatomyositis), raised CK.	CK, EMG, biopsy, autoantibodies.	Steroids, immunosuppression, physio.
Metabolic/Endocrine ⚖️	Electrolyte or hormonal disorders.	Hypokalaemia → flaccid weakness; thyroid disease; Cushing’s.	Electrolytes, TFTs, cortisol.	Correct underlying imbalance; hormone therapy.

💡 Clinical Pearls

⚡ Sudden unilateral weakness = stroke until proven otherwise.
🌀 Ascending symmetrical weakness = Guillain-Barré.
🎯 Fluctuating fatigable weakness = myasthenia gravis.
🧠 No sensory involvement = suspect motor neuron disease.
🦴 Back pain + weakness + sphincter issues = spinal cord compression → neurosurgical emergency.

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Limb Weakness