Encephalitis means swelling of the brain and has many different causes. It is often caused by a virus. Herpes Simplex Virus (HSV) is the most common virus that causes encephalitis in the UK.

HSV encephalitis is very rare. It is diagnosed by finding the virus in fluid around the brain and spinal cord. This fluid is called CSF (cerebrospinal fluid). The CSF is obtained by the doctor who performs a lumbar puncture (LP).

HSV encephalitis is treated with the drug aciclovir. Despite treatment, some people are left with significant loss of memory. About 2 out of every 3 people will have memory difficulties long term.

We know dexamethasone can reduce swelling. Reduction in swelling of the brain may improve the recovery of patients with HSV encephalitis.

This study, called DexEnceph, will allow us to compare the recovery of patients that received dexamethasone and those that did not.

There are two reasons why you may have been invited to take part:

• Your doctors have diagnosed you with having HSV encephalitis.

• You may have been invited to take part before the diagnosis is made. This is because your doctors think there is a chance you may have HSV encephalitis. This will mean you have more time to think about taking part.

No not at all. It’s completely up to you. We only want you to take part if you want to. Just tell us if you don’t.

If you decide not to, don’t worry, it won’t change how you are looked after.

If you decide to take part, you will be given this leaflet to keep. You will be asked if you would like to sign a form to say that you understand what will happen and that you are happy to take part. Your parent/carer(s) will also have to sign a form to say they are happy for you to take part.

If you decide to take part that would be really helpful. If you then change your mind, that’s OK as well - you can, and don’t have to say why if you don’t want to.

All patients in the study will receive aciclovir. This is standard treatment for HSV encephalitis.

In addition, if you decide to take part in the study, you may be offered a short course of dexamethasone. This will be decided at random by a computer. This is to be fair, so neither you, your doctor, nor the research team, can choose whether you receive dexamethasone or not. Half of the people in the study will receive dexamethasone and half will not.

If you receive dexamethasone this will be 4 times a day for 4 days. It is given in a line you already have for clinical care.