investigations and diagnosis

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Diagnosistic considerations:
  • check for red flag conditions, such as malignancies, osteoporotic fractures, radiculitis, and cauda equina syndrome
  • considerations for history taking:
    • determine localisation; severity; loss of strength; sensibility disorders; duration; course; influence of coughing, rest, or movement; and consequences for daily activities
  • physical examination - including including neurological testing—for example, straight leg raising test (Lasègue's sign)
    • following tests are indicated in cases with a dermatomal pattern, or positive result on straight leg raising test, or loss of strength or sensibility disorders:
      • reflexes (Achilles or knee tendon),
      • sensibility of lateral and medial sides of feet and toes,
      • strength of big toe during extension,
      • walking on toes and heel (left-right differences)
      • crossed Lasègue's sign

Sciatica should be investigated if:

  • there are red flag symptoms that suggest a serious aetiology including:
    • malignancy
    • infection
  • the patient fails to respond after 6-8 weeks of conservative treatment (1)

Imaging is the most important investigation:

  • MRI is the investigation of choice and is most likely to reveal a prolapsed intervertebral disc
  • the high dose of radiation from CT scanning measn that it cannot be justified if MRI is available
  • plain X-rays are not a reliable investigation in sciatica
  • NICE suggest to consider imaging in specialist settings of care (for example, a musculoskeletal interface clinic or hospital) for people with low back pain with or without sciatica only if the result is likely to change management (2)

Reference:

Last edited 10/2020 and last reviewed 10/2020

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