Neurology
Question 282 of 300
A 50 year old woman present to the Emergency Department complaining of a generalised headache over the last 24 hours which is getting worse, associated with a fever, neck stiffness and photophobia. You note she is confused and disorientated. Lumbar puncture demonstrates lymphocytic CSF, with normal glucose levels. CT head shows an abnormality in the left temporal lobe. Which of the following pathogens is the most likely cause of her symptoms?
Answer:
This picture is most likely due to infective encephalitis, which is most likely caused by herpes simplex virus, which has a predilection for the temporal lobe. In meningitis, meningism is not usually accompanied by confusion unless the infection has spread systemically and caused sepsis and delirium. As such, encephalitis should be considered in any confused patient with meningism.Encephalitis
Neurology
Last Updated: 8th September 2021
Encephalitis is defined as inflammation of the brain parenchyma associated with neurological dysfunction such as altered state of consciousness, seizures, personality changes, cranial nerve palsies, speech problems, and motor and sensory deficits. It is the result of direct inflammation of the brain tissue, as opposed to the inflammation of the meninges (meningitis), and can be the result of infectious or non-infectious causes. An aetiological agent is only identified in around 50% of cases.
Causes
- Viral infections
- Viruses are the main cause of encephalitis, with herpes virus being the most common group of viruses identified.
- Bacterial infections
- Fungal infections
- Parasitic infections
- Para-infectious
- Acute disseminated encephalomyelitis (ADEM)
- Acute haemorrhagic leukoencephalitis
- Bickerstaff's encephalitis
- Rasmussen's encephalitis
- Prion disease
- Creutzfeldt-Jakob disease
- Paraneoplastic (autoimmune) syndromes
- Anti-N-methyl-D-aspartate (NMDA) receptor encephalitis
- Anti-gamma-aminobutyric acid receptor encephalitis
- Encephalomyelitis
- Anti-voltage-gated potassium channel antibody-associated limbic encephalitis/brainstem encephalitis.
Clinical features
- Encephalitis is caused by a heterogeneous group of pathogens, but presents with a near-uniform neurological dysfunction.
- Altered mental status ranging from mild lethargy to profound coma can be seen.
- Cognitive behavioural issues frequently occur, and these include: altered personality, withdrawal, inability to make decisions, akinetic mutism, bizarre behaviour, memory problems, and an amnesic state.
- Seizures of all varieties occur; complex partial seizures are most commonly seen.
- Focal neurological signs (e.g. aphasia, visual disturbances, cranial nerve deficits, lateralised motor weakness, ataxia, tremors, myoclonus, paraplegia, and generalised weakness) are also presenting features.
- Signs of meningoencephalitis (e.g. headache, photophobia, neck stiffness) are present in patients with meningeal inflammation.
- Symptoms and signs of a systemic illness, such as fever or upper respiratory or gastrointestinal symptoms, may precede or occur concurrently with the other presenting features.
Differential diagnosis
- Aseptic/bacterial/fungal meningitis
- Encephalopathy (toxic/metabolic)
- Status epilepticus
- CNS vasculitis
- Malignant hypertension
- Intracranial tumours and cysts
- Neurosarcoidosis
- Systemic lupus erythematosus (SLE)
- Intracranial bleed
- Traumatic brain injury
- Ischaemic stroke
Investigations
A lumbar puncture is always recommended as long as there is no contraindication, and 2 out of the following 4 symptoms are present: fever, headaches, altered mental status of unknown aetiology, meningism.
The main differential to distinguish is encephalopathy secondary to metabolic or toxic disturbances. Once a primary central nervous system disease is diagnosed, the diagnostic approach is geared towards determining the aetiology and appropriate therapy (i.e. finding the appropriate antiviral or antibacterial agents versus immunotherapy).
Routine investigations in all patients should include:
- Cerebrospinal fluid (CSF)
- Opening pressure
- Cell count
- Protein
- Glucose
- Gram stain
- Bacterial culture
- Herpes simplex virus-1/2 polymerase chain reaction (PCR)
- Enterovirus PCR
- Hold for further testing.
- Serum:
- FBC
- Serum electrolytes/liver function test
- Blood cultures
- Hold for further testing.
- Imaging:
- Chest x-ray
- Neuroimaging (MRI is the study of choice).
- Electroencephalogram (all patients with a persistent altered mental status or seizures)
Further investigations are required for specific groups.
Management
- This is a medical emergency; hence, management consists of basic resuscitation measures ensuring adequacy of the airway, breathing, and circulation, and empirical antiviral therapy in cases of suspected viral encephalitis concurrently with diagnostic steps.
- Prompt isolation is required for all forms of encephalitis until the aetiology is determined.
- Aetiology is often unknown, and therefore no specific treatment options exist for the majority of cases. However, for cases where a diagnosis is reasonably certain, treatment is directed towards the underlying offending agent if available.
- Supportive measures:
- Supportive care is the cornerstone of treatment in most cases. This may include endotracheal intubation and mechanical ventilation, circulatory and electrolyte support, management of raised intracranial pressure (ICP), prevention and management of secondary bacterial infections, deep venous thrombosis prophylaxis, and gastrointestinal (ulcer) prophylaxis.
- In patients with elevated ICP, management with corticosteroids and mannitol should be considered. Initial measures are elevation of head of bed to 30° to 45°, avoiding compression of the jugular veins, and hyperventilation to a PaCO2 of around 30. Subsequently, hyperosmolar therapy with mannitol boluses or hypertonic saline can be used to decrease ICP.
- Antiviral treatment
- All cases of suspected community-acquired viral encephalitis are started empirically on aciclovir until the cause is determined. As most cases of sporadic viral encephalitis are secondary to HSV, this is good clinical practice supported by biopsy-proven randomised controlled trials, and it reduces mortality.
- Corticosteroids
- The use of large doses of corticosteroids is controversial. Expert opinion is that they seem to have a significant therapeutic role in certain cases, and in the treatment of some of the complications of encephalitis. The duration of corticosteroid therapy should be short (3 to 5 days) to minimise adverse effects.
- Surgical intervention
- Monitoring devices such as catheters or bolts may be placed to measure ICP. Shunting or surgical decompression (by craniectomy) is indicated in some cases where medical management (corticosteroids, mannitol) has failed to control elevated ICP, and for impending uncal herniation.
- Treatment for non-viral aetiologies
- If the clinical picture and initial tests suggest a non-viral infective encephalitis (bacterial, fungal, parasitic) appropriate antimicrobial therapy is started.
- If cerebrospinal fluid studies do not show a clear infectious aetiology, or the disease manifestation is classic for an autoimmune encephalitis, aggressive immunotherapy with intravenous corticosteroids, immunoglobulin, or plasma exchange should be considered.
Complications
- Death
- Hypothalamic and autonomic dysfunction
- Ischaemic stroke
- Encephalitis lethargica
- Neurological sequelae
- Seizures
- Cerebral haemorrhage
- Cerebral vein thrombosis
- Cerebral vasculitis
- Hydrocephalus
- Post-viral chronic fatigue syndrome
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
