Investigations and diagnosis

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:

• (1) Koes BW et al. Diagnosis and treatment of sciatica. BMJ. 2007 Jun 23;334(7607):1313-7.
• (2) NICE (October 2020). Low back pain and sciatica in over 16s: assessment and management