General MedicineTier 1Approach to a presentation

Undifferentiated presentations - weakness

Red flags

Acute onset focal weakness - stroke until proven otherwise, time-critical
Bilateral ascending weakness - Guillain-Barre syndrome, needs respiratory function monitoring (FVC)
Weakness + bladder/bowel dysfunction + sensory level - spinal cord compression/cauda equina - emergency imaging
Weakness + bulbar symptoms (dysphagia, dysarthria) + respiratory compromise - myasthenic crisis, GBS
Weakness + hyperkalaemia/hypokalaemia - periodic paralysis, treatable metabolic cause

True weakness - localise first

UMN pattern (spasticity, hyperreflexia, upgoing plantar): stroke, spinal cord lesion, MS
LMN pattern (hypotonia, hyporeflexia): peripheral neuropathy (GBS), radiculopathy, anterior horn cell (MND)
Neuromuscular junction: myasthenia gravis (fatigable, ocular/bulbar predominant), Lambert-Eaton (improves with use)
Myopathic: proximal, symmetric - inflammatory myositis, drug-induced (statins, steroids), metabolic

Non-neurological mimics

Profound fatigue (not true weakness) - anaemia, hypothyroidism, depression, deconditioning
Metabolic - hypokalaemia, hypoglycaemia, hyponatraemia
Functional neurological disorder

Onset (sudden vs progressive), pattern (focal/generalised, proximal/distal, symmetric/asymmetric), fatigability
Sensory symptoms, bladder/bowel involvement, bulbar/respiratory symptoms
Preceding infection (GBS - post-diarrhoeal/respiratory illness), medication (statins, steroids)

Tone, power (formally graded), reflexes, plantar response, sensory exam, cranial nerves
Distinguish true weakness from give-way/functional weakness (inconsistency, Hoover's sign)
Respiratory function (FVC) if bulbar/respiratory muscle involvement suspected

Urgent CT/MRI brain or spine depending on localisation and time-course
UEC, calcium, magnesium, CK (myopathy), TSH
Nerve conduction studies/EMG for peripheral/NMJ/myopathic patterns
Lumbar puncture (albuminocytological dissociation in GBS), anti-AChR/anti-MuSK antibodies for myasthenia

Acute stroke pathway if UMN pattern with sudden onset - thrombolysis/thrombectomy window
GBS: IVIG or plasma exchange, monitor FVC closely, ICU if respiratory compromise
Myasthenic crisis: IVIG/plasma exchange, avoid exacerbating drugs (aminoglycosides, some beta-blockers), ICU support if ventilatory failure
Spinal cord compression: urgent imaging, corticosteroids + neurosurgical/oncological decompression if malignant cause
Drug-induced myopathy: stop causative agent (statin, steroid), supportive care
Correct any metabolic cause (potassium, glucose, sodium)

Functional weakness and true neurological weakness can coexist - do not assume functional without appropriate exclusion of organic causes, especially on first presentation
GBS respiratory failure can develop over hours - FVC trend matters more than a single normal value
Statin myopathy is frequently missed if CK isn't checked in a patient with new proximal weakness on a statin
Cauda equina symptoms are time-critical and easily dismissed as "back pain with sciatica"

"Pattern localises the lesion before any test does - UMN, LMN, NMJ or myopathic changes everything downstream."
"Any bulbar or respiratory symptom with weakness gets an FVC, not just a neuro exam."

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