CSF is the clear, colourless, almost acellular fluid (Table 4.3) around the brain, cord, nerve roots and within the ventricles, withdrawn at lumbar puncture (LP). Cervical puncture is now rarely performed. Ventricular CSF is sometimes examined.
Indications for LP and CSF Examination
Principal indications are:
Suspected meningitis and encephalitis – in some cases
Suspected subarachnoid haemorrhage – blood products
Pressure measurement (e.g. idiopathic intracranial hypertension)
Therapeutic CSF removal (e.g. idiopathic intracranial hypertension)Table 4.3 Normal CSF.ObservationCommentAppearanceCrystal clear, colourlessClear when held to light, a.k.a. ‘gin clear’Pressure60–150 mm CSFPatient must be relaxed, recumbent with needle patent for CSF to oscillate in manometerCell count<5/mm3.No polys: mononuclears onlyProtein0.2–0.4 g/LSlightly raised protein <0.7 g/L rarely pathologicalGlucose⅔ to ½ of blood glucoseCSF glucose <½ blood glucose suspiciousCultureSterileDo not accept contaminantsIgG<15% of total CSF proteinUsually only on requestOligoclonal bandsAbsentParallel blood sample
Assays in MS, neurosyphilis, sarcoidosis, Behçet’s, chronic infection, malignant meningitis, polyneuropathy & some dementias.
Intrathecal contrast injection and drugs.
In suspected CNS infection, meticulous attention should focus on examination for cells, cell types and microbiological tests.
Informed Consent, LP Risks, CSF Removal
The procedure should be explained and its potentially painful nature. Written consent should be obtained.
The principal risks relate first to the removal of CSF. CSF often continues to leak around the punctured lumbar dura. This leads to low pressure (low volume) headaches (Chapter 12) and exceptionally to intracranial subdural haematoma.
Secondly, there are local complications at the LP site:
Infection and meningitis
Trauma –pain, nerve root damage
Bleeding, spinal epidural haematoma
Arachnoiditis (Chapter 16).
LP should follow the established procedure. LP should not be performed in the presence of raised intracranial pressure without prior brain imaging and a clear risk appraisal. Inappropriate intrathecal injection of drugs can have fatal consequences.
LP: Contraindications
Suspicion of a mass lesion within the brain or spinal cord. Caudal herniation of the unci and cerebellar tonsils (coning) may occur if an intracranial mass is present and the pressure below is reduced by removal of CSF. Spinal cord compression may worsen, or even develop, if an unsuspected cord tumour is present. Such complications can develop within minutes of LP. Unconscious patients and those with papilloedema must have brain imaging (MRI if feasible), before LP.
Any cause of suspected raised intracranial pressure, without careful consideration.
Local infection near the LP site.
Congenital lumbosacral region abnormalities (e.g. meningo‐myelocoele).
Platelet count < 40 × 109/L; other clotting abnormalities; anticoagulant drugs.
Contraindications are relative: there are circumstances when LP is carried out despite them, for example with papilloedema when idiopathic intracranial hypertension is suspected.
CSF pressure and naked‐eye appearance should be recorded: clear, cloudy, colourless, yellow (xanthochromic), red – and if red, whether or not the colour begins to clear after the first or subsequent sample. Patients should lie flat for 24 hours after LP to avoid subsequent headaches, and drink plenty, both manoeuvres of uncertain value. Analgesics may be needed for post‐LP headaches and occasionally treatments for prolonged low pressure headaches (e.g. epidural autologous blood patches; Chapter 12). Post LP headaches often last several days but may continue for weeks or more.
Biopsy: Brain, Nerve and Muscle
Biopsy of brain, with or without meningeal biopsy is carried for diagnosis of brain tumours, for other mass lesions and other indications, such as chronic infection and vasculitis. Stereotactic procedures are employed increasingly (Chapter 21). Risks are infection, haemorrhage, epilepsy and/or damage to surrounding brain. Morbidity: below 2%.
Peripheral nerve biopsy (sural or radial) is sometimes performed in chronic neuropathies and vasculitis. Risks are few: infection is rare but painful paraesthesiae sometimes follow. A numb patch on the foot is to be expected following sural nerve biopsy.
Muscle biopsy (deltoid or quadriceps) is a standard procedure in many muscle diseases.
Neuropsychological Testing
Cognitive Screening Tests have been mentioned. Detailed testing is sometimes of great value, and outside the remit of a general neurologist. Reports tend to vary in emphasis, some dwelling on psychiatric diagnoses while others focus upon cognitive function.
Intellectual function overall: the Wechsler Adult Intelligence Scale Revised (WAIS‐R) is divided into subtests. The Verbal IQ with the National Adult Reading Test (NART) provides a measure of the premorbid optimal level of function – reading vocabulary is relatively resistant to neurodegenerative processes that degrade cognition. Performance IQ gives a measure of present overall cognitive, especially, non‐verbal ability.
Specific tests address memory functions, language, literacy, calculation, perceptual function, frontal/executive function, attention validity/credibility and effort. The formulation draws together the results: problems with concentration and effort must be given appropriate weighting, especially when pain, depression and anxiety are present.
The Vocabulary of Neurology
This is an overview of patterns we see in practice.
Focal Cortical Disorders
The cortical mantle is highly differentiated. A working knowledge of the cortex is essential, despite the availability of imaging. Beware theories that appear highly specific – the neural network concept is often a more accurate model than attempting to pinpoint a focal lesion – many functions depend upon interactions between cortex and subcortical structures. Here, I summarise some definitions of language disorders and introduce temporal lobe, frontal and parietal problems. There is overlap with Chapter 5 where memory and perception are addressed and common cortical disorders such as aphasia and dementia.
Language and Speech Disorders
Language means that combination of sounds or writing used for interactive communication. A phoneme is its shortest unit.
Dysphasia describes any disorder of language
Dysgraphia: