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Sudden weak leg: In progress

Learning objectives

  • Understand, management of sudden weak leg
  • Differential and mimics
  • Appropriate tests


  • Isolated weak leg can be a stroke presentation often ACA infarct
  • Can easily be confused with other causes of leg weakness
  • We discuss the differentials

Anatomical basis

  • The motor strip precentral (frontal lobe) is Anterior cerebral artery territory
  • Fibres pass through centrum semiovale to post limb of internal capsule.
  • Leg fibres lie laterally in cerebral peducle and pons and decussate in lower medulla
  • Nerve roots are L1 to S3


Causes of Isolated weak leg

ACA infarct Leg weakness mainly. Arm weakness may be seen. May be cognitive issues, apathy, disinhibition, incontinence
Foot drop Foot drop (weakness of the dorsiflexion muscles in the foot) is common, causes difficulty in walking, and greatly increases risk of falling. Spontaneous unilateral foot drop usually has a peripheral cause. The lesion can be in the L5 nerve root, sciatic nerve, common fibular nerve, deep peroneal nerve, or superficial peroneal nerve (figure?). The extent of the sensory or motor deficit depends on the location (or level), severity, and duration of the injury or compression.1

Clinical: Screening tasks



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