Lumbar puncture

Diagnostic lumbar puncture is one of the most commonly performed invasive tests in hospital clinical medicine. Serious complications are rare, and correct technique will minimise diagnostic error and maximise patient comfort.¹²

When to do a lumbar puncture

Indications for lumbar puncture include the following:

• Evaluation of acute headache if a diagnosis such as subarachnoid headache is suspected.

• In the investigation of suspected meningitis.

• To establish a diagnosis in a patient with an acute confusional state.

• To confirm the diagnosis of a demyelinating disorder such as multiple sclerosis.³

• To administer medication such as chemotherapy and some analgesics via the intrathecal route.

• To treat hydrocephalus.

• To diagnose or treat benign intracranial hypertension.⁴

When not to do a lumbar puncture

Contra-indications to LP²⁵

• Signs suggesting raised intracranial pressure:

  • A reduced or fluctuating level of consciousness (Glasgow Coma Scale score less than 9 or a drop of 3 or more).

  • Age-relative bradycardia and hypertension.

  • Focal neurological signs.

  • Abnormal posture or posturing.

  • Unequal, dilated or poorly responsive pupils.

  • Papilloedema.

  • Abnormal 'doll's eye' movements.

  • A tense, bulging fontanelle.

• Shock.

• Extensive or spreading purpura.

• Convulsions until stabilised.

• Coagulation abnormalities.

• Superficial infection at the LP site.

• Respiratory insufficiency, as there is a risk of precipitating respiratory distress.

Complications of lumbar puncture

LP is a relatively safe procedure but some major and minor complications may occur. These should be managed by the clinician or team who did the LP and patients who present to primary care with such complications should be referred back to this team. These include:⁶

• Post-LP headache.

• Infection.

• Bleeding.

• Cerebral herniation (rare but potentially fatal).

• Others (for example, epidermoid tumour, abducens palsy, radicular symptoms and low back pain).

Post-LP headache (PLPH)

⁷

Headache is the most common complication of LP. It lasts for 2-8 days and occurs in around 40% of patients. It is caused by low CSF pressure due to fluid leakage through the hole (so-called 'dural tap'). Typically, it presents in the upright position and is quickly relieved by lying down. The headache is aggravated by coughing or straining and can be associated with nausea, vomiting, vertigo, tinnitus, hearing loss and diplopia. Neck and low backache are also common.

The diagnosis is essentially clinical, based on the history of an LP, the postural nature and the associated symptoms. Examination is usually normal and there are no particular tests to diagnose this complication, though imaging may be done to exclude other causes of the headache. Firm continuous abdominal pressure may improve the headache (by increasing CSF pressure in the intrathecal space) and direct pressure on the jugular vein may worsen it.

Treatment of PLPH⁷

• With pain relief and oral fluids.

• A Cochrane review has shown caffeine to be helpful.⁸

• Intravenous fluids may be used (there is no convincing evidence to support their use but they may help when headache is causing nausea).

• If PLPH still persists, an extradural blood patch can be used. This is where 10-20 ml of the patient's blood is injected into the extradural space.⁹