To diagnose sciatica:

• Rule out serious pathology — see Assessing for serious risks - red flags.
• Confirm that the symptoms and signs are those of sciatica (radiculopathy) by checking that:
• Unilateral leg pain radiates below the knee to the foot or toes.
• Low back pain, if it is present, is less severe than the leg pain.
• There are symptoms and signs of nerve root compression — numbness, tingling (paraesthesia), weakness, or loss of tendon reflexes — all in the distribution of a nerve root.
• Symptoms and signs of nerve compression are (usually) limited to one nerve root.
• Numbness and paraesthesia are in the same distribution.
• Raising the leg whilst it is straight causes greater leg pain and/or more nerve compression symptoms.
• Exclude other causes of similar symptoms and signs — see Differential diagnosis.
• Examination of the hips, knees, and trochanteric bursae will reveal most of the conditions with symptoms similar to sciatica.
• Do not routinely X-ray the spine, as imaging is seldom indicated or useful, and a focused history and the brief clinical examination described is generally sufficient for diagnosis in most people with sciatica [Waddell, 2004; Koes et al, 2007].
• Arrange magnetic resonance imaging (MRI) if:
• There are red flags — imaging will help to confirm or exclude underlying specific conditions.
• Surgery is contemplated — imaging will help decide if surgery is indicated, for example for a herniated lumbar disc.
• For more information on when to arrange MRI, see Referral.

• Pain referred to the upper leg may be more common than sciatica. Pain can be referred to the upper leg from the hip, sacroiliac, and intervertebral facet joints, by a trigger point (an area of soft tissue that is very painful when compressed), and by painful muscles or tendons.
• Conditions that can be confused with sciatica include:
• Sacroiliitis in ankylosing spondylitis and other spondyloarthropathies — with arthropathies, the pain often alternates between buttocks.
• Pyriformis syndrome — the sciatic nerve is compressed or irritated where it is covered by the piriformis muscle. Clinical diagnosis of pyriformis syndrome is difficult, but the syndrome can be excluded if imaging shows compression of the sciatic nerve root by a herniated intervertebral disc.
• Spinal claudication — bilateral calf pain, parasthesia, or numbness on walking.
• Nerve entrapment at the fibular head (peroneal palsy).
• Rarely, thalamic cerebrovascular accident, multiple sclerosis, thoracic spinal fracture, and 'phantom limb' phenomena cause pain similar to that of sciatica. However, these conditions do not have the other neurological symptoms and signs of nerve compression, such as numbness and tingling (paraesthesia), weakness, and loss of tendon reflexes, and (more importantly) they have other more widespread neurological features.
• Cauda equina syndrome — the cauda equina is the bundle of spinal nerves that lead out from the end of the spinal cord. Cauda equina syndrome occurs when these nerves are compressed and damaged. Symptoms include: leg weakness; loss of bowel, bladder, or sexual functions; and changes in sensation around the rectum and genitalia (saddle anaesthesia).

When assessing people with sciatica, check for the presence of 'red flags' for serious conditions, and if any are present, refer or admit the person with appropriate urgency.

Red flags that suggest cauda equina syndrome

• From medical history:
• Saddle anaesthesia or paraesthesia.
• Recent onset of bladder dysfunction (the bladder distends because sensation of fullness is lost; bladder control is lost because there is no sensation when passing urine).
• Recent onset of faecal incontinence (due to loss of sensation of rectal fullness).
• From physical examination:
• Perianal/perineal sensory loss.
• Unexpected laxity of the anal sphincter.
• Severe or progressive neurological deficit in the lower extremities, such as major motor weakness with knee extension, ankle eversion, or foot dorsiflexion.

Red flags that suggest spinal fracture

• From medical history:
• Sudden onset of severe central pain in the spine which is relieved by lying down.
• Major trauma such as a road accident or fall from a height.
• Minor trauma, or even just strenuous lifting, in people with osteoporosis.
• From physical examination:
• Structural deformity of the spine (such as a step from one vertebra to an adjacent vertebra).

Red flags that suggest cancer or infection

• From medical history:
• Onset in people older than 50 years, or younger than 20 years, of age.
• History of cancer.
• Constitutional symptoms, such as fever, chills, or unexplained weight loss.
• Recent bacterial infection (for example urinary tract infection).
• Intravenous drug abuse.
• Immune suppression.
• Pain that remains when supine, aching night-time pain that disturbs sleep, and thoracic pain (which also suggests aortic aneurysm).
• From physical examination:
• Structural deformity of the spine (such as scoliosis).

Red flags that suggest a high risk of permanent damage to the compressed nerve

• Significant muscle weakness or wasting.
• Loss of tendon reflexes.
• Presence of a positive Babinski reflex — when the lateral part of the sole of the foot is stimulated, the toes extend and fan outwards.

• Red flags are indicators of increased risk of serious pathology — they do not always indicate that a specific condition is present.
• For example, pain that remains when lying supine does not mean that the person has cancer or infection of the spine. But it does mean that these conditions should be more readily suspected.
• Further investigation and referral with appropriate urgency may be indicated, and should always be considered, if one or more red flags are present.
• Clinical judgement should be used to decide how urgently to refer when red flags suggest a serious condition. The presence of red flags does not always mean that emergency admission is required (serious does not always mean an emergency).
• For example, cauda equina syndrome would usually warrant immediate admission, but referral to be seen within a few days might be appropriate for suspected cancer secondaries in the spine.
• Serious underlying pathology is not common.
• Red flags should be explicitly looked for. For example, the person may not report symptoms such as perineal numbness unless asked.
• For more information on causes of sciatic symptoms, see Differential diagnosis.

These recommendations are derived from national and international guidelines, which are largely based on expert opinion [NICE, 2001; NZGG, 2004; van Tulder et al, 2004; Waddell, 2004; Health Education Board for Scotland and Health and Safety Executive, 2008; WeMeReC, 2008].