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weakness of the lower limb(s) / weak in the knees


  • weakness of the legs has a multitude of possible causes and it helps to determine the pattern of weakness:
    • are the arms involved
      • if so, it is unlikely to be a lower spinal cause
      • is it one leg with ipsilateral arm?
    • is it bilateral and symmetric
      • does it spare sensory nerves and reflexes
        • cause is most likely at level of muscle or NM junction rather than at the spine
      • is it proximal > distal
      • is there bladder/anal involvement to suggest cauda equina syndrome (CES) (these symptoms can also be caused by transverse myelitis)
        • urgent MRI scan is warranted
    • is it confined to one leg?
      • is the leg ischaemic?
      • are the reflexes brisk?
        • suggests upper motor neuron lesion:
        • if reflex not brisk, suggests lower motor neuron lesion
          • compartment syndrome
          • lumbar disc prolapse
          • nerve injury / neuropraxia
    • is the patient febrile with back pain?
      • could it be an epidural abscess
      • urgent MRI scan is warranted unless explanation for fever is adequate to avoid MRI

bilateral symmetric leg weakness

sparing of upper limb involvement

  • most likely either:
  • less common causes:
      • mainly lower legs with associated sensory involvement, and as it progresses, arms are usually involved as well
    • periodic hypokalaemic paralysis
      • hereditary, usually 1st episode in adolescence or as young adults
      • usually have onset in the morning and last a few hours to days
    • myositis
      • especially if associated with thigh pain and raised creatinine kinase levels
      • polymyositis (PM) / dermatomyositis (100-200 cases per million)
        • sporadic form mainly in the elderly -50 cases per million in those aged over 50 years
        • IBM2 hereditary form mainly in Iranian Jew ethnicity, presenting at age 20-40yrs with proximal leg weakness but sparing of quadriceps
    • uncommonly, an intracranial cause
      • single cause affecting only both legs is rare (eg. midline brain lesion), although normal pressure hydrocephalus tends to cause gait disturbance and incontinence
      • more common would be a multifocal process but then upper limb and /or face or other neurology would be expected
      • consider if other symptoms such as headaches, memory difficulties, etc.
    • is there oculobulbar features
    • if dry mouth is a feature, consider:
      • myelopathy associated with Sjögren's syndrome
      • if no eye features, but develops autonomic dysfunction within 3 months of onset, then consider Lambert-Eaton myasthenic syndrome (3 cases per million, and half will have an associated cancer, mostly small cell lung cancer)
    • other systemic conditions
    • muscular dystrophies
      • eg. Duchenne's muscular dystrophy

with upper limb involvement

ED work up

  • history and exam with particular focus on discriminating findings as above such as UL vs LL, sensory vs motor, red flags of cauda equina syndrome (CES) or spinal infection, or a spinal “level” for a lesion
  • check post-void bladder scan
  • FWT urine
  • baseline bloods - FBE, U&E, LFTs, CRP, (CK if suspect myositis), (blood cultures if suspect infection)
  • urgent CT brain if:
    • stroke (CVA) or other intracranial cause seems likely (this is especially the case if ipsilateral arm and leg are involved)
    • NB. consider contrast scan if high risk of intracranial neoplasia or focal infection
  • urgent MRI spine if
  • consider urgent neurology or neurosurgical referral as indicated
weakness_ll.txt · Last modified: 2020/05/21 19:56 by gary1