Microbiology
Infections
Question 32 of 77
A 50 year old woman present to ED 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.Infective Encephalitis
Microbiology / Infections
Last Updated: 18th June 2019
Encephalitis is inflammation within the substance of the central nervous system.
Infective Agents
- Herpes simplex virus (most common cause)
- Temporal lobe is most frequently affected
- Virus replication in neurons, followed by the oedema associated with the inflammatory response accounts for the haemorrhagic necrosis and space-occupying nature of this form of the disease
- Varicella zoster virus
- Cytomegalovirus
- Arbovirus
- Mumps
- Measles
Clinical Disease
- Fever
- Headache
- Neck stiffness
- Impaired consciousness
- Focal neurological signs
- Seizures
Diagnosis
- Lumbar puncture
- Viral encephalitis leads to a lymphocytosis with normal CSF/plasma glucose ratio
- Elevated CSF to serum antibody ratios indicate CSF infection with the respective organism
- PCR analysis of CSF can be used to diagnose most viral infections
- Blood FBC, biochemistry, film, serology and cultures
- CT/MRI head may demonstrate focal lesions
- EEG
Treatment
- Treatment of herpes simplex encephalitis is with intravenous aciclovir
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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 |
