Why sudden leg weakness matters
Weakness that comes on over hours is an emergency until the cause is known. Some causes are in the spine or the nerves, but others are in the blood, and a few of those can stop the heart, so an ECG and blood chemistry belong at the start, not the end.
What to ask in the history
- When it started, which muscles, and whether it is spreading to the arms or breathing
- Numbness, tingling, back pain, bladder or bowel problems
- His kidney disease: the cause, dialysis or not, any missed sessions, how much urine he passes
- Recent changes in diet or fluid intake
- Medicines: diuretics, blood pressure tablets, supplements, painkillers, anything new
- Palpitations, chest pain, fainting
- Vomiting, diarrhoea, recent infection
Red flags
- Weakness spreading to the arms or breathing muscles
- Palpitations, a slow or irregular pulse, fainting
- Any abnormality on the ECG
- Very little or no urine
- Back pain with bladder or bowel loss
- Low blood pressure
What to examine
- Airway, breathing, circulation; pulse rate and rhythm, blood pressure
- Fluid status: overloaded or dry
- Tone, power, reflexes and sensation in the legs and arms; a sensory level on the trunk
- How well he breathes and coughs
- Signs of advanced kidney disease; dialysis access
First investigations
- ECG straight away, and continuous cardiac monitoring
- Blood gas with electrolytes, which gives the quickest result
- Kidney function, electrolytes including calcium, magnesium and phosphate
- Glucose
- Creatine kinase
- Full blood count
- MRI of the spine if the examination points to the cord
Differential diagnosis of sudden leg weakness
Grouped, not ranked. Which one fits this patient is for you to work out in the case.
Spine and nerves
- Spinal cord compression
- Guillain-Barre syndrome
In the blood
- High or low potassium
- Abnormal calcium or magnesium
- Severe uraemia
- Low glucose
Muscle
- Rhabdomyolysis
- Myopathy, including from medicines
Brain
- Stroke (usually one-sided)
Common mistakes
- Sending him for a spine scan before checking the blood chemistry and the ECG.
- Leaving him without cardiac monitoring while results are awaited.
- Dismissing an abnormal potassium as a bad sample without repeating it and checking the ECG.