see also:

• neurology
• weakness_UL
• gait disturbance
• paraesthesiae or numbness

• NB. in a trauma context, spinal cord injury and other traumatic causes need to be considered
• atraumatic weakness of the legs has a multitude of possible causes and it helps to determine the pattern of weakness:
  • if there is chest pain, abdominal pain or back pain, consider aortic dissection
  • are the arms involved
    • if so, it is unlikely to be a lower spinal cause
    • is it one leg with ipsilateral arm?
      • if so, it is likely to be a hemiplegic stroke (CVA)
    • if all four limbs are involved and patient is alert, consider a metabolic cause (check potassium, phosphate, calcium, TSH levels), spinal TIA, transverse myelitis, myositis (check CK), or other causes (see below)
  • 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?
      • see peripheral vascular disease (PVD or PAD)
    • are the reflexes brisk?
      • suggests upper motor neuron lesion:
        • stroke (CVA)
        • brain tumour (+ acute haemorrhage if acute onset)
        • spinal cord compression ⇒ urgent MRI spine if no other cause evident
      • 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

• most likely either:
  • muscle wasting
    • frailty of old age (sarcopenia / generalised muscle wasting)
    • immobility
    • malnutrition
    • cachexia
    • chronic disease
    • motor neurone disease (MND) with LMN features
  • thoracic or lumbar spine aetiology
    • lumbar disc prolapse - bilateral signs suggest central prolapse and risk of cauda equina syndrome (CES)
    • neoplasia of spine
    • epidural abscess if fever and back pain
    • trauma to spine
    • transverse myelitis
• less common causes:
  • peripheral neuropathy
    • 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
  • early phase of Guillain-Barre syndrome (GBS)
  • myositis
    • especially if associated with thigh pain and raised creatinine kinase levels
    • statins
    • polymyositis (PM) / dermatomyositis (100-200 cases per million)
    • inclusion body myositis (IBM)
      • 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
    • consider myasthenia gravis (150 cases per million)
  • if dry mouth is a feature, consider:
    • myelopathy associated with Sjögren's syndrome (SS)
    • 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
    • paraneoplastic syndromes including paraneoplastic limbic encephalitis such as is associated with anti-Hu antibodies in association with small cell lung cancer
    • systemic lupus erythematosus (SLE)
  • muscular dystrophies
    • eg. Duchenne's muscular dystrophy

• this would imply cervical level cord involvement

• periodic hypokalaemic paralysis
  • hereditary, usually 1st episode in adolescence or as young adults
• periodic hyperkalaemic paralysis
• periodic normo-kalaemic paralysis
  • most are associated with hyperthyroidism
  • very rarely can be familial mutation
• transient spinal cord ischaemia / spinal cord TIA
  • see below under ongoing weakness for more details - most spinal TIAs have a good recovery and no cause found and seem to only rarely develop a future spinal cord infarct

• acute spinal cord compression
  • eg. tumours, abscess
• transverse myelitis
  • usually acute onset associated with a viral illness
• Guillain-Barre syndrome (GBS) - acute ascending weakness
• intracranial pathology including stroke (CVA), tumours, abscess, etc
  • usually these are unilateral but rarely may be bilateral
• peripheral neuropathy
  • mainly lower legs with associated sensory involvement, and as it progresses, arms are usually involved as well
• motor neurone disease (MND)
  • slowly progressive weakness
• myositis if CK is high
• syringomyelia
  • rare, most present as young adults with progressive weakness +/- incontinence, but some may have a more acute onset following sneezing or coughing
• syringobulbia
• spinal cord ischaemia / spinal TIA:
  • acutely impaired blood supply may result in an acute myelopathy with onset within minutes but may be a few hours in some cases
  • most patients have back or neck pain at the onset of symptoms and this is localized to the level of the lesion and ~ half were precipitated by movement which presumably compromised the blood supply to the cord ¹⁾
  • some have a TIA-like presentation and most of these are cervical
  • some developed post-recovery hyperalgesia
  • most have a good recovery although those which arise following aortic surgery or involve the conus are more likely to have a poor recovery
  • no cause is found in most patients but other patients may have preceding prolonged hypotension or disc prolapse
    • rarely, it may be a form of intermittent claudication or arterial steal such as when there are recurrent attacks associated with an activity such as gardening
• some other conditions as under sparing of arms

• 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
  • suspect acute spinal cord compression, cauda equina syndrome (CES), transverse myelitis, spinal ischaemia or spinal infection
  • NB. this may be restricted to lumbar spine if only LMN signs and suspect cauda equina syndrome (CES) primarily
  • NB. if UMN signs may need to do whole spine
• consider urgent neurology or neurosurgical referral as indicated